Certificate Management

The cert-manager manages TLS certificates in Kubernetes clusters using custom resources.

In a multi-cluster environment like Gardener, using existing open source projects for certificate management like cert-manager becomes cumbersome. With this project the separation of concerns between multiple clusters is realized more easily. The cert-controller-manager runs in a secured cluster where the issuer secrets are stored. At the same time it watches an untrusted source cluster and can provide certificates for it. The cert-controller-manager relies on DNS challenges (ACME only) for validating the domain names of the certificates. For this purpose it creates DNSEntry custom resources (in a possible separate dns cluster) to be handled by the companion dns-controller-manager from external-dns-management.

Currently, the cert-controller-manager supports certificate authorities via:

• Automatic Certificate Management Environment (ACME) protocol like Let's Encrypt.
• Certificate Authority (CA): an existing certificate and a private key provided as a TLS Secret.

Index

• Quick start using certificates in a Gardener shoot cluster
• Setting up Issuers
  • Automatic Certificate Management Environment (ACME)
    • Auto registration
    • Using existing account
  • Certificate Authority (CA)
  • SelfSigned
• Requesting a Certificate
  • Using commonName and optional dnsNames
  • Follow CNAME
  • Preferred Chain
  • Secret Labels
  • Specifying private key algorithm and size
  • Using a certificate signing request (CSR)
  • Creating JKS or PKCS#12 keystores
• Requesting a Certificate for Ingress
  • Process
• Requesting a Certificate for Service
• Requesting a Certificate for Gateways
  • Istio gateways
  • Gateway API gateways
• Demo quick start
• Using the cert-controller-manager
  • Usage
• Renewal of Certificates
• Revoking Certificates
  • Revoking certificates with renewal
  • Checking OCSP revocation using OpenSSL
• Metrics
• Using DNSRecords
• Troubleshooting
• Development
• Why not use the community cert-manager solution?

Quick start using certificates in a Gardener shoot cluster

This component is typically deployed by the Gardener Extension for certificate services to simplify requesting certificates for Gardener shoot clusters.

For a quick start please see Request X.509 Certificates

Setting up Issuers

Before you can obtain certificates from a certificate authority (CA), you need to set up an issuer. The issuer is specified in the default cluster, while the certificates are specified in the source cluster.

The issuer custom resource contains the configuration and registration data for your account at the CA.

Automatic Certificate Management Environment (ACME)

Two modes are supported:

• auto registration
• using an existing account

Auto registration

Auto registration is mainly used for development and test environments. You only need to provide the server URL and an email address. The registration process is done automatically for you by creating a private key and performing the registration at the CA. Optionally you can provide the target secret with the privateKeySecretRef section.

For example see examples/20-issuer-staging.yaml:

apiVersion: cert.gardener.cloud/v1alpha1
kind: Issuer
metadata:
  name: issuer-staging
  namespace: default
spec:
  acme:
    server: https://acme-staging-v02.api.letsencrypt.org/directory
    email: [email protected]
    autoRegistration: true
    # with 'autoRegistration: true' a new account will be created if the secretRef is not existing
    privateKeySecretRef:
      name: issuer-staging-secret
      namespace: default

Using existing account

If you already have an existing account at the certificate authority, you need to specify email address and reference the private key from a secret.

apiVersion: v1
kind: Secret
metadata:
  name: my-issuer-secret
  namespace: default
type: Opaque
data:
  privateKey: LS0tLS1...

apiVersion: cert.gardener.cloud/v1alpha1
kind: Issuer
metadata:
  name: my-issuer
  namespace: default
spec:
  acme:
    server: https://acme-v02.api.letsencrypt.org/directory
    email: [email protected]
    privateKeySecretRef:
      name: my-issuer-secret
      namespace: default

In both cases, the state of an issuer resource can be checked on the default cluster with

▶ kubectl get issuer
NAME             SERVER                                                   EMAIL                    STATUS   TYPE   AGE
issuer-staging   https://acme-staging-v02.api.letsencrypt.org/directory   [email protected]   Ready    acme   8s

Certificate Authority (CA)

This issuer is meant to be used where a central Certificate Authority is already in place. The operator must request/provide by its own means a CA or an intermediate CA. This is mainly used for on-premises and air-gapped environments.

To create a self-signed certificate a dedicated issuer of type selfSigned should be used.

It is also possible to manually create a self-signed certificate using the CA issuer

Manual steps

Create a Self-signed Certificate Authority

▶ openssl genrsa -out CA-key.pem 4096
▶ export CONFIG="
[req]
distinguished_name=dn
[ dn ]
[ ext ]
basicConstraints=CA:TRUE,pathlen:0
"
▶ openssl req \
    -new -nodes -x509 -config <(echo "$CONFIG") -key CA-key.pem \
    -subj "/CN=Hello" -extensions ext -days 1000 -out CA-cert.pem

Create a TLS secret from the certificate CA-cert.pem and the private key CA-key.pem

▶ kubectl -n default create secret tls issuer-ca-secret \
    --cert=CA-cert.pem --key=CA-key.pem -oyaml \
    --dry-run=client > secret.yaml

The content of the secret.yaml should look like the following, for a full example see examples/20-issuer-ca.yaml

apiVersion: v1
data:
  tls.crt: {base64 certificate}
  tls.key: {base64 private key}
kind: Secret
metadata:
  name: issuer-ca-secret
type: kubernetes.io/tls

Apply the secrets in the cluster and create the issuer, for example see examples/20-issuer-ca.yaml

---
apiVersion: cert.gardener.cloud/v1alpha1
kind: Issuer
metadata:
  name: issuer-ca
  namespace: default
spec:
  ca:
    privateKeySecretRef:
      name: issuer-ca-secret
      namespace: default

The state of the issuer resource can be checked on the default cluster with

▶ kubectl get issuer
NAME        SERVER   EMAIL   STATUS   TYPE   AGE
issuer-ca                    Ready    ca     6s

Some details about the CA can be found in the status of the issuer.

▶ kubectl get issuer issuer-ca -ojsonpath='{.status}' | jq '.'
{
  "ca": {
    "NotAfter": "2023-05-31T14:55:55Z",
    "NotBefore": "2020-09-03T14:55:55Z",
    "Subject": {
      "CommonName": "my-domain.com",
      "Country": [
        "DE"
      ],
      "Locality": [
        "Walldorf"
      ],
      "Organization": [
        "Gardener"
      ],
      "OrganizationalUnit": [
        "Gardener"
      ],
      "PostalCode": null,
      "Province": [
        "BW"
      ],
      "SerialNumber": "1E04A2C8F057AC890F45FEC5446AE4DDA73EA1D5",
      "StreetAddress": null
    }
  },
  "observedGeneration": 1,
  "requestsPerDayQuota": 10000,
  "state": "Ready",
  "type": "ca"
}

SelfSigned

This issuer is meant to be used when you want to create a fully managed self-signed certificate.

Configure your shoot to allow custom issuers in the shoot cluster. By default, issuers are created in the control plane of your cluster.

kind: Shoot
...
spec:
  extensions:
  - type: shoot-cert-service
    providerConfig:
      apiVersion: service.cert.extensions.gardener.cloud/v1alpha1
      kind: CertConfig
      shootIssuers:
        enabled: true # if true, allows to specify issuers in the shoot cluster
...

Create and deploy a self-signed issuer in your shoot cluster (examples/20-issuer-selfsigned.yaml)

apiVersion: cert.gardener.cloud/v1alpha1
kind: Issuer
metadata:
  name: issuer-selfsigned
  namespace: default
spec:
  selfSigned: {}

Create a certificate (examples/30-cert-selfsigned.yaml). Please note that spec.isCA must be set to true to create a self-signed certificate. The duration (life-time) of the certificate as well as the private key algorithm and key size may be specified. Duration value must be in units accepted by Go time.ParseDuration (see here), and it must be greater than 720h (30 days).

apiVersion: cert.gardener.cloud/v1alpha1
kind: Certificate
metadata:
  name: cert-selfsigned
  namespace: default
spec:
  commonName: cert1.mydomain.com
  isCA: true
  # optional: default is 90 days (2160h). Must be greater 30 days (720h)
  # duration: 720h1m
  # optional defaults to RSA 2048
  #privateKey:
  #  algorithm: ECDSA
  #  size: 384
  issuerRef:
    name: issuer-selfsigned
    namespace: default  # must be specified when issuer runs in shoot!
  # optional: secret where the certificate should be stored
  #secretRef:
  #  name: cert-selfsigned-foo
  #  namespace: default

Requesting a Certificate

To obtain a certificate for a domain, you specify a certificate custom resource on the source cluster. You can specify the issuer explicitly by reference. If there is no issuer reference, the default issuer is used (provided as command line option). You must either specify the commonName and further optional dnsNames or you can also start with a certificate signing request (CSR).

For domain validation, the cert-controller-manager only supports DNS challenges. For this purpose it relies on the dns-controller-manager from the external-dns-management project. If any domain name (commonName or any item from dnsNames) needs to be validated, it creates a custom resource DNSEntry in the dns cluster. When the certificate authority sees the temporary DNS record, the certificate is stored in a secret finally. The name of the secret can be specified explicitly with secretName and will be stored in the same namespace as the certificate on the source cluster.

The certificate is checked for renewal periodically. The renewal is performed automatically and the secret is updated. Default values for periodical check is daily, the certificate is renewed if its validity expires within 60 days.

Using commonName and optional dnsNames

For example see examples/30-cert-simple.yaml:

apiVersion: cert.gardener.cloud/v1alpha1
kind: Certificate
metadata:
  name: cert-simple
  namespace: default
spec:
  commonName: cert1.mydomain.com
  dnsNames:
  - cert1-foo.mydomain.com
  - cert1-bar.mydomain.com
  # if issuer is not specified, the default issuer is used
  issuerRef:
    name: issuer-staging

Follow CNAME

This option is useful if a delegated domain for DNS01 challenge should be used. If you don't have permissions for the DNS hosted zone to write the DNS record for the challenge, you can ask the domain owner to provide a CNAME record to domain name in a writable hosted zone.

Example:

Assume you want to request a certificate for my-service.example-domain.com, but you only have write permissions for the hosted zone sandbox.other-domain.com.

1. The owner of example-domain.com adds this CNAME DNS record

   _acme-challenge.my-service.example-domain.com -> _acme-challenge.my-service.sandbox.other-domain.com

2. Set followCNAME: true in the certificate spec

   apiVersion: cert.gardener.cloud/v1alpha1
   kind: Certificate
   metadata:
     name: cert-follow
     namespace: default
   spec:
     commonName: my-service.example-domain.com
     followCNAME: true

In this case, the cert-management controller will see the CNAME record and write the TXT record for the DNS challenge to the target, i.e. _acme-challenge.my-service.sandbox.other-domain.com.

If you are using an annotated ingress or service resource, the option is set by the annotation cert.gardener.cloud/follow-cname=true.

Preferred Chain

If the CA offers multiple certificate chains, you can select the chain with the optional preferredChain field. The value is the Subject Common Name of the issuer. If no match, the default offered chain will be used. Please consult the documentation of the ACME server about offered certificate chains.

Example:

apiVersion: cert.gardener.cloud/v1alpha1
kind: Certificate
metadata:
  name: cert-follow
  namespace: default
spec:
  commonName: my-service.example-domain.com
  preferredChain: "ISRG Root X1"

Secret Labels

The secretLabels section allows to specify labels to be set for the certificate secret.

Example:

apiVersion: cert.gardener.cloud/v1alpha1
kind: Certificate
metadata:
  name: cert-secret-labels
  namespace: default
spec:
  commonName: my-service.example-domain.com
  secretName: my-secret
  secretLabels:
    key1: value1
    key2: value2

In this case the secret my-secret will contains the labels.

Specifying private key algorithm and size

The private key algorithm and size used by default are deployment specific. To override these defaults, you may override them in the certificate itself. Please note, that changing these values will lead to an immediate renewal of the certificate. In case the default values have changed in the deployment, and you have not overwritten it, the new default values will only apply to new certificates or when a certificate is renewed.

Note: The default algorithm and sizes can be overwritten by command line arguments --default-private-key-algorithm, --default-rsa-private-key-size, --default-ecdsa-private-key-size

Add the privateKey section to specify private key algorithm and/or size.

Example:

apiVersion: cert.gardener.cloud/v1alpha1
kind: Certificate
metadata:
  name: cert-ecdsa
  namespace: default
spec:
  commonName: my-service.example-domain.com
  secretName: my-secret
  privateKey:
    algorithm: ECDSA
    size: 384

Allowed values for spec.privateKey.algorithm are RSA and ECDSA. For RSA, the allowed key sizes are 2048, 3072, and 4096. If the size field is not specified, a deployment specific default value will be used. For ECDSA, the allowed key sizes are 256 and 384. If the size field is not specified, a deployment specific default value will be used.

Using a certificate signing request (CSR)

You can provide a complete CSR in PEM format (and encoded as Base64).

For example see examples/30-cert-csr.yaml:

apiVersion: cert.gardener.cloud/v1alpha1
kind: Certificate
metadata:
  name: cert-csr
  namespace: default
spec:
  csr: LS0tLS1CRUd...
  issuerRef:
    name: issuer-staging

⚠️ Using a CSR is only available for ACME Issuer

Creating JKS or PKCS#12 keystores

By default, the certificate secret contains the TLS certificate using the standard data entries tls.key, tls.crt and ca.crt.

With the keystores section in the certificate spec, bundles in the form of JKS or PKCS#12 keystores can be requested to be stored in the secret additionally. For the JKS (Java keystore) format, the additional data entries are keystore.jks and truststore.jks. For PKCS#12 format, the data entries are named keystore.p12 and truststore.p12. In both cases, the keystore file contains all the data, but the truststore file only the CA. The keystores are secured by the password as provided with the secret/key pair passwordSecretRef.

For example see examples/30-cert-simple-with-keystores.yaml:

apiVersion: cert.gardener.cloud/v1alpha1
kind: Certificate
metadata:
  name: cert-simple-with-keystores
  namespace: default
spec:
  commonName: ...

  # enable keystore creation for both JKS and PKCS#12
  # This will create additional data entries in the certificate secret named `keystore.jks`, `truststore.jks` for JKS
  # and `keystore.p12`, `truststore.p12` for PKCS#12
  keystores:
    jks:
      create: true
      passwordSecretRef:
        secretName: keystore-secret
        key: password
    pkcs12:
      create: true
      passwordSecretRef:
        secretName: keystore-secret
        key: password  

Requesting a Certificate for Ingress

Add the annotation cert.gardener.cloud/purpose: managed to the Ingress resource. The cert-controller-manager will then automatically request a certificate for all domains given by the hosts in the tls section of the Ingress spec.

For compatibility with the Gardener Cert-Broker, you can alternatively use the deprecated label garden.sapcloud.io/purpose: managed-cert for the same outcome.

See also examples/40-ingress-echoheaders.yaml:

Process

1. Create the Ingress Resource (optional)

   In order to request a certificate for a domain managed by cert-controller-manager an Ingress is required. In case you don’t already have one, take the following as an example:

   apiVersion: networking.k8s.io/v1
   kind: Ingress
   metadata:
     name: vuejs-ingress
   spec:
     tls:
     # Gardener managed default domain.
     # The first host is used as common name if it does not exceed 64 characters
     - hosts:
       - test.ingress.<GARDENER-CLUSTER>.<GARDENER-PROJECT>.shoot.example.com
       # Certificate and private key reside in this secret.
       secretName: testsecret-tls
     rules:
     - host: test.ingress.<GARDENER-CLUSTER>.<GARDENER-PROJECT>.shoot.example.com
       http:
         paths:
         - backend:
             service:
               name: vuejs-svc
               port:
                 number: 8080
           path: /
           pathType: Prefix

   2. Annotate the Ingress Resource

      The annotation cert.gardener.cloud/purpose: managed instructs cert-controller-manager to handle certificate issuance for the domains found in labeled Ingress.

      apiVersion: networking.k8s.io/v1
      kind: Ingress
      metadata:
        name: tls-example-ingress
        annotations:
          # Let Gardener manage certificates for this Ingress.
          cert.gardener.cloud/purpose: managed
          #dns.gardener.cloud/class: garden                             # needed on Gardener shoot clusters for managed DNS record creation (if not covered by `*.ingress.<GARDENER-CLUSTER>.<GARDENER-PROJECT>.shoot.example.com)
          #cert.gardener.cloud/commonname: "*.demo.mydomain.com"        # optional, if not specified the first name from spec.tls[].hosts is used as common name
          #cert.gardener.cloud/dnsnames: ""                             # optional, if not specified the names from spec.tls[].hosts are used
          #cert.gardener.cloud/follow-cname: "true"                     # optional, to activate CNAME following for the DNS challenge
          #cert.gardener.cloud/secret-labels: "key1=value1,key2=value2" # optional labels for the certificate secret
          #cert.gardener.cloud/issuer: issuer-name                      # optional to specify custom issuer (use namespace/name for shoot issuers)
          #cert.gardener.cloud/preferred-chain: "chain name"            # optional to specify preferred-chain (value is the Subject Common Name of the root issuer)
          #cert.gardener.cloud/private-key-algorithm: ECDSA             # optional to specify algorithm for private key, allowed values are 'RSA' or 'ECDSA'
          #cert.gardener.cloud/private-key-size: "384"                  # optional to specify size of private key, allowed values for RSA are "2048", "3072", "4096" and for ECDSA "256" and "384"
          # annotations needed when using DNSRecords
          #cert.gardener.cloud/dnsrecord-provider-type: aws-route53
          #cert.gardener.cloud/dnsrecord-secret-ref: myns/mysecret
      spec:
        tls:
          - hosts:
              - echoheaders.demo.mydomain.com
            secretName: cert-echoheaders
        rules:
          - host: echoheaders.demo.mydomain.com
            http:
              paths:
                - backend:
                    service:
                      name: echoheaders
                      port:
                        number: 80
                  path: /
                  pathType: Prefix

      The annotation cert.gardener.cloud/commonname can be set to explicitly specify the common name. If no set, the first name of spec.tls.hosts is used as common name. The annotation cert.gardener.cloud/dnsnames can be used to explicitly specify the alternative DNS names. If no set, the names of spec.tls.hosts are used.

2. Check status

   A certificate custom resource is created in the same namespace of the source cluster. You can either check the status of this certificate resource with kubectl get cert or you can check the events for the ingress with kubectl get events

   The certificate is stored in the secret as specified in the Ingress resource.

Requesting a Certificate for Service

If you have a service of type LoadBalancer, you can use the annotation cert.gardener.cloud/secretname together with the annotation dns.gardener.cloud/dnsnames from the dns-controller-manager to trigger automatic creation of a certificate. If you want to share a certificate between multiple services and ingresses, using the annotations cert.gardener.cloud/commonname and cert.gardener.cloud/dnsnames may be helpful.

apiVersion: v1
kind: Service
metadata:
  annotations:
    cert.gardener.cloud/secretname: test-service-secret
    dns.gardener.cloud/dnsnames: test-service.demo.mydomain.com
    #dns.gardener.cloud/class: garden                             # needed on Gardener shoot clusters for managed DNS record creation
    #cert.gardener.cloud/commonname: "*.demo.mydomain.com"        # optional, if not specified the first name from dns.gardener.cloud/dnsnames is used as common name
    #cert.gardener.cloud/dnsnames: ""                             # optional, if specified overrides dns.gardener.cloud/dnsnames annotation for certificate names
    #cert.gardener.cloud/follow-cname: "true"                     # optional, to activate CNAME following for the DNS challenge
    #cert.gardener.cloud/secret-labels: "key1=value1,key2=value2" # optional labels for the certificate secret
    #cert.gardener.cloud/issuer: issuer-name                      # optional to specify custom issuer (use namespace/name for shoot issuers)
    #cert.gardener.cloud/preferred-chain: "chain name"            # optional to specify preferred-chain (value is the Subject Common Name of the root issuer)
    #cert.gardener.cloud/private-key-algorithm: ECDSA             # optional to specify algorithm for private key, allowed values are 'RSA' or 'ECDSA'
    #cert.gardener.cloud/private-key-size: "384"                  # optional to specify size of private key, allowed values for RSA are "2048", "3072", "4096" and for ECDSA "256" and "384"
    #cert.gardener.cloud/secret-namespace: "my-namespace"         # optional to specify the namespace where the certificate secret should be created
    # annotations needed when using DNSRecords
    #cert.gardener.cloud/dnsrecord-provider-type: aws-route53
    #cert.gardener.cloud/dnsrecord-secret-ref: myns/mysecret
    dns.gardener.cloud/ttl: "600"
  name: test-service
  namespace: default
spec:
  ports:
  - name: http
    port: 80
    protocol: TCP
    targetPort: 8080
  type: LoadBalancer

The annotation cert.gardener.cloud/commonname is optional. If not specified, the first name of the annotation dns.gardener.cloud/dnsnames is used as common name if it does not exceed 64 characters. It is useful to specify it explicitly, if no DNSEntry should be created for the common name by the dns-controller-manager. A typical use case is if the common name (limited to 64 characters) is set only to deal with real domain names specified with dns.gardener.cloud/dnsnames which are longer than 64 characters. The annotation cert.gardener.cloud/dnsnames can be used to explicitly specify the alternative DNS names. If set, it overrides the values from the annotation dns.gardener.cloud/dnsnames for the certificate (but not for creating DNS records by the dns-controller-manager).

If you want to share a certificate between multiple services and ingresses, using the annotations cert.gardener.cloud/commonname and cert.gardener.cloud/dnsnames may be helpful. For example, to share a wildcard certificate, you should add these two annotations

    cert.gardener.cloud/commonname: "*.demo.mydomain.com"
    cert.gardener.cloud/dnsnames: ""

This will create or reuse a certificate for *.demo.mydomain.com. An existing certificate is automatically reused, if it has exactly the same common name and DNS names.

The annotation cert.gardener.cloud/secret-namespace can be used to change the namespace, the TLS secret is created in. By default, it is created in the same namespace as the service.

Requesting a Certificate for Gateways

There are source controllers for Gateways from Istio or the new Kubernetes Gateway API. By annotating the Gateway resource with the cert.gardener.cloud/purpose=managed annotation, certificates are managed automatically for the hosts.

Istio gateways

For Istio, gateways for API versions networking.istio.io/v1, networking.istio.io/v1beta1, and networking.istio.io/v1alpha3 are supported.

To enable automatic management of Certificate resources, annotate the Istio Gateway resource with cert.gardener.cloud/purpose=managed. The domain names are extracted from the spec.servers.hosts field and from the field spec.hosts of related VirtualService resources.

apiVersion: networking.istio.io/v1
kind: Gateway
metadata:
  annotations:
    cert.gardener.cloud/purpose: managed
    #cert.gardener.cloud/commonname: "*.demo.mydomain.com"        # optional, if not specified the first name from spec.tls[].hosts is used as common name
    #cert.gardener.cloud/dnsnames: ""                             # optional, if not specified the names from spec.tls[].hosts are used
    #cert.gardener.cloud/follow-cname: "true"                     # optional, to activate CNAME following for the DNS challenge
    #cert.gardener.cloud/secret-labels: "key1=value1,key2=value2" # optional labels for the certificate secret
    #cert.gardener.cloud/issuer: issuer-name                      # optional to specify custom issuer (use namespace/name for shoot issuers)
    #cert.gardener.cloud/preferred-chain: "chain name"            # optional to specify preferred-chain (value is the Subject Common Name of the root issuer)
    #cert.gardener.cloud/private-key-algorithm: ECDSA             # optional to specify algorithm for private key, allowed values are 'RSA' or 'ECDSA'
    #cert.gardener.cloud/private-key-size: "384"                  # optional to specify size of private key, allowed values for RSA are "2048", "3072", "4096" and for ECDSA "256" and "384"
    #cert.gardener.cloud/secret-namespace: "istio-system"         # optional to specify the namespace where the certificate secret should be created
    # annotations needed when using DNSRecords
    #cert.gardener.cloud/dnsrecord-provider-type: aws-route53
    #cert.gardener.cloud/dnsrecord-secret-ref: myns/mysecret
  name: my-gateway
  namespace: default
spec:
  selector:
    istio: ingressgateway
  servers:
    - hosts:
        - uk.example.com
        - eu.example.com
      port:
        name: https-443
        number: 443
        protocol: HTTPS
      tls:                         # this server is ignored by the cert-controller-manager, as `tls.credentialName` is not set
        mode: SIMPLE
        privateKey: /etc/certs/privatekey.pem
        serverCertificate: /etc/certs/servercert.pem
    - hosts:
        - bookinfo-namespace/*.example2.com
      port:
        name: https-9443
        number: 9443
        protocol: HTTPS
      tls:
        credentialName: my-secret  # only servers with credentialName will be considered
        mode: SIMPLE

In this case, only a Certificate resource would be created with domain name *.example2.com, as the first server item specifies no tls.credentialName field.

The annotation cert.gardener.cloud/secret-namespace can be used to change the namespace, the TLS secret is created in. By default, it is created in the same namespace as the gateway object.

See the Istio tutorial for a more detailed example.

Gateway API gateways

The Gateway API versions gateway.networking.k8s.io/v1 and gateway.networking.k8s.io/v1beta1 are supported.

To enable automatic management of Certificate resources, annotate the Gateway API Gateway resource with cert.gardener.cloud/purpose=managed. The domain names are extracted from the spec.listeners.hostnames field and from the field spec.hostnames of related HTTPRoute resources.

apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  annotations:
    cert.gardener.cloud/purpose: managed
    #cert.gardener.cloud/commonname: "*.demo.mydomain.com"        # optional, if not specified the first name from spec.tls[].hosts is used as common name
    #cert.gardener.cloud/dnsnames: ""                             # optional, if not specified the names from spec.tls[].hosts are used
    #cert.gardener.cloud/follow-cname: "true"                     # optional, to activate CNAME following for the DNS challenge
    #cert.gardener.cloud/secret-labels: "key1=value1,key2=value2" # optional labels for the certificate secret
    #cert.gardener.cloud/issuer: issuer-name                      # optional to specify custom issuer (use namespace/name for shoot issuers)
    #cert.gardener.cloud/preferred-chain: "chain name"            # optional to specify preferred-chain (value is the Subject Common Name of the root issuer)
    #cert.gardener.cloud/private-key-algorithm: ECDSA             # optional to specify algorithm for private key, allowed values are 'RSA' or 'ECDSA'
    #cert.gardener.cloud/private-key-size: "384"                  # optional to specify size of private key, allowed values for RSA are "2048", "3072", "4096" and for ECDSA "256" and "384"
    # annotations needed when using DNSRecords
    #cert.gardener.cloud/dnsrecord-provider-type: aws-route53
    #cert.gardener.cloud/dnsrecord-secret-ref: myns/mysecret
  name: my-gateway
  namespace: default
spec:
  gatewayClassName: my-gateway-class
  listeners:
    - allowedRoutes:
        namespaces:
          from: Selector
          selector:
            matchLabels:
              shared-gateway-access: "true"
      hostname: foo.example.com
      name: https
      port: 443
      protocol: HTTPS
      tls:
        certificateRefs:
          - name: my-tls-secret      # note: listeners are only considered if they have exactly one certificateRefs item

In this case, a single Certificate resource with domain name foo.example.com would be created.

See the Gateway API tutorial for a more detailed example.

Demo quick start

1. Run dns-controller-manager with:

   ./dns-controller-manager --controllers=azure-dns --identifier=myOwnerId --disable-namespace-restriction

2. Ensure provider and its secret, e.g.

   kubectl apply -f azure-secret.yaml
   kubectl apply -f azure-provider.yaml

   • check with

     ▶ kubectl get dnspr
     NAME               TYPE        STATUS   AGE
     azure-playground   azure-dns   Ready    28m

3. Create test namespace

   kubectl create ns test

4. Run cert-controller-manager

   ./cert-controller-manager

5. Register user [email protected] at Let's Encrypt

   kubectl apply -f examples/20-issuer-staging.yaml

   • check with

     ▶ kubectl get issuer
     NAME             SERVER                                                   EMAIL                    STATUS   TYPE   AGE
     issuer-staging   https://acme-staging-v02.api.letsencrypt.org/directory   [email protected]   Ready    acme   8s

6. Request a certificate for cert1.my-domain.com

   kubectl apply -f examples/30-cert-simple.yaml

   If this certificate has been already registered for the same issuer before, it will be returned immediately from the ACME server. Otherwise, a DNS challenge is started using a temporary DNSEntry to be set by dns-controller-manager

   • check with

     ▶ kubectl get cert -o wide
     NAME          COMMON NAME           ISSUER           STATUS   EXPIRATION_DATE        DNS_NAMES                 AGE
     cert-simple   cert1.mydomain.com    issuer-staging   Ready    2019-11-10T09:48:17Z   [cert1.my-domain.com]     34s

Using the cert-controller-manager

The cert-controller-manager communicates with up to four different clusters:

• default used for managing issuers and lease management. The path to the kubeconfig is specified with command line option --kubeconfig.
• source used for watching resources ingresses, services and certificates The path to the kubeconfig is specified with command line option --source. If option is omitted, the default cluster is used for source.
• dns used to write temporary DNSEntries for DNS challenges The path to the kubeconfig is specified with command line option --dns. If option is omitted, the default cluster is used for dns.
• target used for storing generated certificates (and issuers if --allow-target-issuers option is set) The path to the kubeconfig is specified with command line option --target. If option is omitted, the source cluster is also used for target.

Usage

The complete list of options is:

Usage:
  cert-controller-manager [flags]

Flags:
      --accepted-maintainers string                              accepted maintainer key(s) for crds
      --acme-deactivate-authorizations                           if true authorizations are always deactivated after each ACME certificate request
      --allow-target-issuers                                     If true, issuers are also watched on the target cluster
      --bind-address-http string                                 HTTP server bind address
      --cascade-delete                                           If true, certificate secrets are deleted if dependent resources (certificate, ingress) are deleted
      --cert-class string                                        Identifier used to differentiate responsible controllers for entries
      --cert-target-class string                                 Identifier used to differentiate responsible dns controllers for target entries
      --config string                                            config file
  -c, --controllers string                                       comma separated list of controllers to start (<name>,<group>,all)
      --cpuprofile string                                        set file for cpu profiling
      --default-ecdsa-private-key-size int                       Default certificate private key size for 'ecdsa' algorithm.
      --default-issuer string                                    name of default issuer (from default cluster)
      --default-issuer-domain-ranges string                      domain range restrictions when using default issuer separated by comma
      --default-private-key-algorithm string                     default algorithm for certificate private keys
      --default-requests-per-day-quota int                       Default value for requestsPerDayQuota if not set explicitly in the issuer spec.
      --default-rsa-private-key-size int                         Default certificate private key size for 'rsa' algorithm.
      --default.pool.resync-period duration                      Period for resynchronization for pool default
      --default.pool.size int                                    Worker pool size for pool default
      --disable-namespace-restriction                            disable access restriction for namespace local access only
      --dns string                                               cluster for writing challenge DNSEntries or DNSRecords
      --dns-class string                                         class for creating challenge DNSEntries (in DNS cluster)
      --dns-namespace string                                     namespace for creating challenge DNSEntries or DNSRecords (in DNS cluster)
      --dns-owner-id string                                      ownerId for creating challenge DNSEntries
      --dns.disable-deploy-crds                                  disable deployment of required crds for cluster dns
      --dns.id string                                            id for cluster dns
      --dns.migration-ids string                                 migration id for cluster dns
      --force-crd-update                                         enforce update of crds even they are unmanaged
      --grace-period duration                                    inactivity grace period for detecting end of cleanup for shutdown
  -h, --help                                                     help for cert-controller-manager
      --httproutes.pool.size int                                 Worker pool size for pool httproutes
      --ingress-cert.cert-class string                           Identifier used to differentiate responsible controllers for entries of controller ingress-cert
      --ingress-cert.cert-target-class string                    Identifier used to differentiate responsible dns controllers for target entries of controller ingress-cert
      --ingress-cert.default.pool.resync-period duration         Period for resynchronization for pool default of controller ingress-cert
      --ingress-cert.default.pool.size int                       Worker pool size for pool default of controller ingress-cert
      --ingress-cert.pool.resync-period duration                 Period for resynchronization of controller ingress-cert
      --ingress-cert.pool.size int                               Worker pool size of controller ingress-cert
      --ingress-cert.target-name-prefix string                   name prefix in target namespace for cross cluster generation of controller ingress-cert
      --ingress-cert.target-namespace string                     target namespace for cross cluster generation of controller ingress-cert
      --ingress-cert.targets.pool.size int                       Worker pool size for pool targets of controller ingress-cert
      --issuer-namespace string                                  namespace to lookup issuers on default cluster
      --issuer.acme-deactivate-authorizations                    if true authorizations are always deactivated after each ACME certificate request of controller issuer
      --issuer.allow-target-issuers                              If true, issuers are also watched on the target cluster of controller issuer
      --issuer.cascade-delete                                    If true, certificate secrets are deleted if dependent resources (certificate, ingress) are deleted of controller issuer
      --issuer.cert-class string                                 Identifier used to differentiate responsible controllers for entries of controller issuer
      --issuer.default-ecdsa-private-key-size int                Default certificate private key size for 'ecdsa' algorithm. of controller issuer
      --issuer.default-issuer string                             name of default issuer (from default cluster) of controller issuer
      --issuer.default-issuer-domain-ranges string               domain range restrictions when using default issuer separated by comma of controller issuer
      --issuer.default-private-key-algorithm string              default algorithm for certificate private keys of controller issuer
      --issuer.default-requests-per-day-quota int                Default value for requestsPerDayQuota if not set explicitly in the issuer spec. of controller issuer
      --issuer.default-rsa-private-key-size int                  Default certificate private key size for 'rsa' algorithm. of controller issuer
      --issuer.default.pool.resync-period duration               Period for resynchronization for pool default of controller issuer
      --issuer.default.pool.size int                             Worker pool size for pool default of controller issuer
      --issuer.dns-class string                                  class for creating challenge DNSEntries (in DNS cluster) of controller issuer
      --issuer.dns-namespace string                              namespace for creating challenge DNSEntries or DNSRecords (in DNS cluster) of controller issuer
      --issuer.dns-owner-id string                               ownerId for creating challenge DNSEntries of controller issuer
      --issuer.issuer-namespace string                           namespace to lookup issuers on default cluster of controller issuer
      --issuer.issuers.pool.size int                             Worker pool size for pool issuers of controller issuer
      --issuer.pool.resync-period duration                       Period for resynchronization of controller issuer
      --issuer.pool.size int                                     Worker pool size of controller issuer
      --issuer.precheck-additional-wait duration                 additional wait time after DNS propagation check of controller issuer
      --issuer.precheck-nameservers string                       Default DNS nameservers used for checking DNS propagation. If explicity set empty, it is tried to read them from /etc/resolv.conf of controller issuer
      --issuer.propagation-timeout duration                      propagation timeout for DNS challenge of controller issuer
      --issuer.renewal-overdue-window duration                   certificate is counted as 'renewal overdue' if its validity period is shorter (metrics cert_management_overdue_renewal_certificates) of controller issuer
      --issuer.renewal-window duration                           certificate is renewed if its validity period is shorter of controller issuer
      --issuer.revocations.pool.size int                         Worker pool size for pool revocations of controller issuer
      --issuer.secrets.pool.size int                             Worker pool size for pool secrets of controller issuer
      --issuer.use-dnsrecords                                    if true, DNSRecords (using Gardener Provider extensions) are created instead of DNSEntries of controller issuer
      --issuers.pool.size int                                    Worker pool size for pool issuers
      --istio-gateways-dns.cert-class string                     Identifier used to differentiate responsible controllers for entries of controller istio-gateways-dns
      --istio-gateways-dns.cert-target-class string              Identifier used to differentiate responsible dns controllers for target entries of controller istio-gateways-dns
      --istio-gateways-dns.default.pool.resync-period duration   Period for resynchronization for pool default of controller istio-gateways-dns
      --istio-gateways-dns.default.pool.size int                 Worker pool size for pool default of controller istio-gateways-dns
      --istio-gateways-dns.pool.resync-period duration           Period for resynchronization of controller istio-gateways-dns
      --istio-gateways-dns.pool.size int                         Worker pool size of controller istio-gateways-dns
      --istio-gateways-dns.target-name-prefix string             name prefix in target namespace for cross cluster generation of controller istio-gateways-dns
      --istio-gateways-dns.target-namespace string               target namespace for cross cluster generation of controller istio-gateways-dns
      --istio-gateways-dns.targets.pool.size int                 Worker pool size for pool targets of controller istio-gateways-dns
      --istio-gateways-dns.targetsources.pool.size int           Worker pool size for pool targetsources of controller istio-gateways-dns
      --istio-gateways-dns.virtualservices.pool.size int         Worker pool size for pool virtualservices of controller istio-gateways-dns
      --k8s-gateways-dns.cert-class string                       Identifier used to differentiate responsible controllers for entries of controller k8s-gateways-dns
      --k8s-gateways-dns.cert-target-class string                Identifier used to differentiate responsible dns controllers for target entries of controller k8s-gateways-dns
      --k8s-gateways-dns.default.pool.resync-period duration     Period for resynchronization for pool default of controller k8s-gateways-dns
      --k8s-gateways-dns.default.pool.size int                   Worker pool size for pool default of controller k8s-gateways-dns
      --k8s-gateways-dns.httproutes.pool.size int                Worker pool size for pool httproutes of controller k8s-gateways-dns
      --k8s-gateways-dns.pool.resync-period duration             Period for resynchronization of controller k8s-gateways-dns
      --k8s-gateways-dns.pool.size int                           Worker pool size of controller k8s-gateways-dns
      --k8s-gateways-dns.target-name-prefix string               name prefix in target namespace for cross cluster generation of controller k8s-gateways-dns
      --k8s-gateways-dns.target-namespace string                 target namespace for cross cluster generation of controller k8s-gateways-dns
      --k8s-gateways-dns.targets.pool.size int                   Worker pool size for pool targets of controller k8s-gateways-dns
      --kubeconfig string                                        default cluster access
      --kubeconfig.disable-deploy-crds                           disable deployment of required crds for cluster default
      --kubeconfig.id string                                     id for cluster default
      --kubeconfig.migration-ids string                          migration id for cluster default
      --lease-duration duration                                  lease duration
      --lease-name string                                        name for lease object
      --lease-renew-deadline duration                            lease renew deadline
      --lease-resource-lock string                               determines which resource lock to use for leader election, defaults to 'leases'
      --lease-retry-period duration                              lease retry period
  -D, --log-level string                                         logrus log level
      --maintainer string                                        maintainer key for crds (default "cert-controller-manager")
      --name string                                              name used for controller manager (default "cert-controller-manager")
      --namespace string                                         namespace for lease (default "kube-system")
  -n, --namespace-local-access-only                              enable access restriction for namespace local access only (deprecated)
      --omit-lease                                               omit lease for development
      --plugin-file string                                       directory containing go plugins
      --pool.resync-period duration                              Period for resynchronization
      --pool.size int                                            Worker pool size
      --precheck-additional-wait duration                        additional wait time after DNS propagation check
      --precheck-nameservers string                              Default DNS nameservers used for checking DNS propagation. If explicity set empty, it is tried to read them from /etc/resolv.conf
      --propagation-timeout duration                             propagation timeout for DNS challenge
      --renewal-overdue-window duration                          certificate is counted as 'renewal overdue' if its validity period is shorter (metrics cert_management_overdue_renewal_certificates)
      --renewal-window duration                                  certificate is renewed if its validity period is shorter
      --revocations.pool.size int                                Worker pool size for pool revocations
      --secrets.pool.size int                                    Worker pool size for pool secrets
      --server-port-http int                                     HTTP server port (serving /healthz, /metrics, ...)
      --service-cert.cert-class string                           Identifier used to differentiate responsible controllers for entries of controller service-cert
      --service-cert.cert-target-class string                    Identifier used to differentiate responsible dns controllers for target entries of controller service-cert
      --service-cert.default.pool.resync-period duration         Period for resynchronization for pool default of controller service-cert
      --service-cert.default.pool.size int                       Worker pool size for pool default of controller service-cert
      --service-cert.pool.resync-period duration                 Period for resynchronization of controller service-cert
      --service-cert.pool.size int                               Worker pool size of controller service-cert
      --service-cert.target-name-prefix string                   name prefix in target namespace for cross cluster generation of controller service-cert
      --service-cert.target-namespace string                     target namespace for cross cluster generation of controller service-cert
      --service-cert.targets.pool.size int                       Worker pool size for pool targets of controller service-cert
      --source string                                            source cluster to watch for ingresses and services
      --source.disable-deploy-crds                               disable deployment of required crds for cluster source
      --source.id string                                         id for cluster source
      --source.migration-ids string                              migration id for cluster source
      --target string                                            target cluster for certificates
      --target-name-prefix string                                name prefix in target namespace for cross cluster generation
      --target-namespace string                                  target namespace for cross cluster generation
      --target.disable-deploy-crds                               disable deployment of required crds for cluster target
      --target.id string                                         id for cluster target
      --target.migration-ids string                              migration id for cluster target
      --targets.pool.size int                                    Worker pool size for pool targets
      --targetsources.pool.size int                              Worker pool size for pool targetsources
      --use-dnsrecords                                           if true, DNSRecords (using Gardener Provider extensions) are created instead of DNSEntries
  -v, --version                                                  version for cert-controller-manager
      --virtualservices.pool.size int                            Worker pool size for pool virtualservices
      --watch-gateways-crds.default.pool.size int                Worker pool size for pool default of controller watch-gateways-crds
      --watch-gateways-crds.pool.size int                        Worker pool size of controller watch-gateways-crds

Renewal of Certificates

Certificates created with an ACME issuer are automatically renewed. With the standard configuration, the certificate is renewed 30 days before it validity expires. For example, if Let's Encrypt is used as certificate authority, a certificate is always valid for 90 days and will be rolled 30 days before it expires by updating the referenced Secret in the Certificate object.
The configuration can be changed with the command line parameter --issuer.renewal-window.

Revoking Certificates

Certificates created with an ACME issuer can also be revoked if private key of the certificate is no longer safe. This page about Revoking certificates on Let's Encrypt list various reasons:

For instance, you might accidentally share the private key on a public website; hackers might copy the private key off of your servers; or hackers might take temporary control over your servers or your DNS configuration, and use that to validate and issue a certificate for which they hold the private key.

Revoking a certificate is quite simple. You create a CertificateRevocation object on the source cluster with a reference to the Certificate object to be revoked.

apiVersion: cert.gardener.cloud/v1alpha1
kind: CertificateRevocation
metadata:
  name: revoke-sample
  namespace: default
spec:
  certificateRef:
    name: mycert
    namespace: default
    
  # Uncomment the following line if certificate should be renewed before revoking the old one(s)
  #renew: true
  
  # Optionally specify a qualifying date. All certificates requested before this date will be revoked.
  # If not specified, the current time is used by default.
  #qualifyingDate: "2020-12-22T17:00:35Z"

The cert-controller-manager will then perform several steps.

1. Using the certificate secret it looks for other Certificate objects using the same certificate. The "same" certificate means same issuer, Common Name, and DNS Names. All found objects will be reconciled too.

2. It will look for other valid certificate secrets older than the qualifying date. Concretely this will deal with unused certificates, which are still valid. As a certificate is renewed 30 days before the end of validity, the old certificate is still valid, but not used anymore.

3. All found certificate secrets are revoked and marked with an annotation cert.gardener.cloud/revoked: "true"

4. The state of all found Certificate objects is set to Revoked

5. The state of the CertificateRevocation object is set to Applied. Additionally, the status of the CertificateRevocation object contains more details about revoked objects and secrets:

   apiVersion: cert.gardener.cloud/v1alpha1
   kind: CertificateRevocation
   metadata:
     name: revoke-sample
     namespace: default
   spec:
     certificateRef:
       name: mycert
       namespace: default
     qualifyingDate: "2020-12-22T17:00:35Z"
   status:
     message: certificate(s) revoked
     objects:
       revoked:
       - name: mycert
         namespace: default
     revocationApplied: "2020-12-22T17:09:32Z"
     secrets:
       revoked:
       - name: cert-backup-default-issuer-8a7e93f7-sks7p
         namespace: kube-system
         serialNumber: fa:3f:9a:5e:ac:47:ee:d1:91:a6:31:a7:43:6f:8a:7e:93:f7
     state: Applied

   The secrets listed in the status are only the internal backups maintained by the cert-controller-manager. The actual secrets used by the Certificate objects are not listed, but nonetheless marked as revoked.

Revoking certificates with renewal

With this variant the certificate is renewed, before the old one(s) are revoked. This means the certificate secrets of the Certificate objects will contain newly requested certificates and the old certificate(s) will be revoked afterward.

For this purpose, set renew: true in the spec of the CertificateRevocation object:

apiVersion: cert.gardener.cloud/v1alpha1
kind: CertificateRevocation
metadata:
  name: revoke-sample
  namespace: default
spec:
  certificateRef:
    name: mycert
    namespace: default
  renew: true

In this case, the status will list the renewed Certificate objects:

apiVersion: cert.gardener.cloud/v1alpha1
kind: CertificateRevocation
metadata:
  name: revoke-sample
  namespace: default
spec:
  certificateRef:
    name: mycert
    namespace: default
  renew: true
  qualifyingDate: "2020-12-22T17:00:35Z"
status:
  message: certificate renewed and old certificate(s) revoked
  objects:
    renewed:
    - name: mycert
      namespace: default
  revocationApplied: "2020-12-22T17:09:32Z"
  secrets:
    revoked:
    - name: cert-backup-default-issuer-8a7e93f7-sks7p
      namespace: kube-system
      serialNumber: fa:3f:9a:5e:ac:47:ee:d1:91:a6:31:a7:43:6f:8a:7e:93:f7
  state: Applied

Checking OCSP revocation using OpenSSL

To verify the OCSP revocation of the X509 certificate of a Certificate object, you can use the tool hack/check-cert-secret.sh in this repository.

Usage:

hack/check-cert-secret.sh check-revoke mynamespace mycertname

Here mynamespace and mycertname are the namespace and the name of the certificate object.

Metrics

Metrics are exposed for Prometheus if the command line option --server-port-http <port> is specified. The endpoint URL is http://<pod-ip>:<port>/metrics. Besides the default Go metrics, the following cert-management specific metrics are provided:

Name	Labels	Description
cert_management_acme_account_registrations	uri, email, issuer	ACME account registrations
cert_management_acme_orders	issuer, success, dns_challenges, renew	Number of ACME orders
cert_management_cert_entries	issuer, issuertype	Total number of certificate objects per issuer
cert_management_cert_object_expire	namespace, name	Expire date as Unix time (the number of seconds elapsed since January 1, 1970 UTC)
cert_management_acme_active_dns_challenges	issuer	Currently active number of ACME DNS challenges
cert_management_overdue_renewal_certificates	-	Number of certificate objects with certificate's renewal overdue
cert_management_revoked_certificates	-	Number of certificate objects with revoked certificate
cert_management_secrets	classification	Number of certificate secrets per classification (only updated on startup and every 24h on GC of secrets). Currently there are three classifications: total = total number of certificate secrets on the source cluster, revoked = number of revoked certificate secrets, backup= number of backups of certificate secrets (every certificate has a backup secret in the kube-system namespace to allow revocation even if it is not used anymore)

Using DNSRecords

With the command line option --use-dnsrecords, the cert-controller-manager creates DNSRecords resources instead of DNSEntries. In this case, the Certificate or source objects need two additional annotations:

• cert.gardener.cloud/dnsrecord-provider-type to fill the .spec.type field of DNSRecords
• cert.gardener.cloud/dnsrecord-secret-ref to fill the .spec.secretRef. The value is either the name of the secret in the same namespace as the certificate or in the format <namespace>/<name>.

Troubleshooting

Requesting certificates from an ACME provider (like Let's Encrypt) is always performed using a DNS01 challenge. For this purpose, the cert-controller-manager creates an DNSEntry for the dns-controller-manager (see project external-dns-management). Your dns-controller-manager needs a suitable DNSProvider responsible for the domain(s) of the common name and further DNS names of the certificate. It will create a DNS TXT record in the corresponding zone. This DNS TXT record must be visible to the ACME issuer. In case of Let's encrypt this means the DNS record must be available to the public internet. If the certificate fails with an event obtaining certificate failed: error: one or more domains had a problem, there are a lot of possible reasons. Here are the two most frequent ones.

1. You see a Warning event with Failed check: DNS entry getting ready like

   LAST SEEN   TYPE      REASON      OBJECT               MESSAGE
   20m         Warning   reconcile   certificate/mycert   obtaining certificate failed: error: one or more domains had a problem: [mycert.<mydomain>] time limit exceeded . Details: DNS TXT record '_acme-challenge.mycert.<mydomain>' is not visible on public (or precheck) name servers. Failed check: DNS entry getting ready

   This means there is a problem with the DNSEntry which is not getting ready. Either there was no suitable DNSProvider for this domain, or the provider is not ready itself (e.g. invalid credentials) Please note that this DNSEntry is deleted automatically if a try to request the certificate request is finished.

2. You see a Warning event with Failed check: DNS record propagation like

   LAST SEEN   TYPE      REASON      OBJECT               MESSAGE
   10m         Warning   reconcile   certificate/mycert   obtaining certificate failed: error: one or more domains had a problem: [mycert.<mydomain>] time limit exceeded . Details: DNS TXT record '_acme-challenge.mycert.<mydomain>' is not visible on public (or precheck) name servers. Failed check: DNS record propagation

   This means the DNS TXT record could not be looked up by the configured "precheck" nameservers. With the default configuration, these are some public DNS servers. In this case, check if the configured DNSProvider uses a private hosted zone or if the "precheck" nameservers need to be adjusted to your use case. There may also some configuration of the hosted zone itself (i.e. generic CNAME forwarding) which may cause problems.

Development

For development please see Development documentation

Why not use the community cert-manager solution?

Some of the reasons for developing our own solution relate to Gardener's highly dynamic requirements. The following list differentiates reasons based on the effort that would be required to adapt cert-manager to our needs.

⚠️ is used to indicate that a difference exists, but it could be resolved with a reasonable effort.

⛔️ is used to indicate that overcoming the difference would require a significant effort.

1. ⚠️ CertificateSigningRequests (CSR) are supported via a custom resource in the cert-manager project (ref). Gardener's cert-management supports CSRs via the csr spec field of the Certificate resource.

2. ⚠️ The FollowCNAME options is only supported on the Issuer resource in the cert-manager project (ref). Gardener's cert-management allows to configure the followCNAME option on the Certificate resource.

3. ⚠️ CertificateRevocations are not supported in the cert-manager project.

4. ⚠️ Only Kubernetes Gateway resources can be annotated in the cert-manager project (ref). Gardener's cert-management supports both Kubernetes Gateway and Istio Gateway resources.

5. ⚠️ It is not possible to annotate Service resources of type LoadBalancer in the cert-manager project (ref).

6. ⛔️ There is no reuse of existing certificates in the cert-manager project. This means that if a certificate is requested multiple times, it will be issued multiple times. Gardener's cert-management reuses existing certificates if the common name and DNS names match.

7. ⛔️ The ACME DNS-01 challenge is represented through the custom resources DNSEntry and DNSRecord in the cert-manager project. Gardener's cert-management uses the companion dns-controller-manager from external-dns-management to solve DNS-01 challenges (possibly in a separate DNS cluster). This would require developing a webhook Issuer for cert-manager to integrate with the dns-controller-manager (ref).

8. ⛔️ Private keys for the ACME Issuer have to be stored in the same cluster as the cert-manager controller is running in (ref). This is an essential requirement for a hosted control-plane solution like Gardener, where issuers and especially their secrets should remain opaque to end-users. Gardener's cert-management allows to separate Issuer and Certificate resources in different clusters.

9. ⛔️ There's no dynamic watch support for Istio Gateway resources in the cert-manager project since it only supports Kubernetes Gateways. In Gardener's cert-management the cert-controller-manager automatically restarts itself when the Istio Gateway CRD is installed to start watching the resources.

The cert-management authors are open to align the projects more closely in the future if the gaps can be overcome.