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Terraform Template to Setup a Kubernetes Cluster on OpenStack/AWS/Azure

This project contains a terraform environment to setup a kubernetes cluster in various IaaS environments. The following IaaS layers are supported yet:

  • Openstack
  • AWS
  • Azure

Kubify supports cluster setup, recovery from an etcd backup file and rolling of cluster nodes. A cluster update is possible as long as the contained components can just be redeployed and the update is done by a rolling update by the kubernetes controllers. The update of the kubelets is supported without rolling the nodes.

The target cluster can be enriched by a set of predefinied addons that comes out of the box with this template project.

For the technical launch of a cluster bootkube is used on CoreOS VMs.

The setup is completely handled by a single terraform project, which uses specific terraform modules handling IaaS related tasks. Recovery is handled by a specific bootstrap etcd deployment together with the regular bootkube mechanism.

Kubify is designed to be used as a git submodule for a cluster specific project that hosts a specific cluster's configuration and the selection of a cluster variant (openstack/aws/azure). Here also the terraform state is stored which enables performing cluster modifications later based on the same terraform project.

Cluster Environment

Bastion and Node Access

Remote access to cluster nodes can be restricted by a bastion VM. Using a bastion allows omitting public access to every cluster node. Node access will automatically use the bastion host. It is also possible to assign public IP addresses to every node, in this case no bastion host is required.

Bootstrapping

All nodes are fully configured by a cloud-init file. Active parts are handled by systemd services. The kubelet is run by using the kubelet wrapper mechanism provided by CoreOS. Therefore always CoreOS images are used for the cluster nodes. The kubelet version is controlled by a dedicated file. In case this is changed the kubelet service is automatically restarted. This can be used to implement version upgrades of kubelets without requiring reinstallation of nodes.

The cluster is bootstrapped using bootkube. Bootstrapping is always done by the first (index 0) master node. Therefore a bootkube service is configured on master nodes. It automatically starts when an appropriate configuration file is present. The bootkube configuration is prepared by terraform and propagated to the first master node by a remote provisioner. This is done exactly once. On subsequent calls to terraform an appropriate auto terraform configuration file is generated which disables the bootstrap resource in order to avoid repeated bootstrapping.

Recovery

Kubify supports cluster recovery from an etcd backup file. Recovery uses the terraform project used to setup the cluster by enabling the recovery mode and executing terraform apply, again. In recovery mode the master nodes and volumes are recreated and the cluster bootstrap is reinitiated using the etcd backup in order to initialize the bootstrap etcd cluster. This is the only difference compared to an initial cluster setup.

ETCD

The current setup uses a self hosted etcd approach supported by bootkube and the etcd operator. The etcd is scaled with the master nodes and uses a persistent volume for their persistence. For bootrapped clusters the etcd operator does not support kubernetes volumes, therefore a VM volume for master nodes is created and used to back the host path used by the etcd cluster

API Server

The API Server can only run on master nodes. It uses the node port 443. This is used to create a load balancer for this port and the set of master nodes.

Ingress

The same mechanism is used to statically provide a load balancer for the nginx ingress controller for http(s) access. The nginx pods are running on the worker nodes, only. Here the ports 80 and 443 are used as node ports on the worker nodes.

Basically nginx could also use a load balancer created by a service object, but then it would not be possible to generate the DNS and load balancer environment in advance using terraform. This could be changed if either the public IP assigned to the load balancer could be configured by the service object or if there would be a DNS controller in Kubernetes. But then the constraint for the IaaS layer is to offer (???) load balancers with dedicated public IPs. This is, for example, not the case for AWS (???). Always using statically provided load balancers for the ingress should works for all environments.

Rolling updates of nodes.

If the configuration of master or worker nodes require a recreation of VMs, this is done by upating each node with a separate call to terraform apply one by one. With every successfull execution the update of the next master/worker node is triggered. This is completely implemented by the terraform configuration files and by keeping the actual state in a separate json file which can later again be read as a terraform variable file (auto file). Configuration variables allow to configure the behaviour of node rolling.

Setup a new cluster

  • Create a new git repository representing the desired new cluster This repository is used to keep track of the used terraform template version, the terraform configuration and state of the cluster.

    mkdir <cluster-name>
cd <cluster-name>
git init
git remote add origin <git repository url>

  • Prepare the cluster project content

    Add a .gitignore file

    .terraform/
terraform/
gen/
tmp/
.sw[opq]

  • Add the kubify repository as a git submodule with the name k8s.

    git submodule add https://github.com/gardener/kubify.git k8s
git submodule init

  • Select the cluster IaaS variant to be used Create a symbolic link variant pointing to the variant to use. Variants are stored in folder variants inside the submodule residing in folder k8s.

    Currently three variants are supported

    • openstack
    • aws
    • azure

    For example:

    ln -s k8s/variants/openstack variant

    Starting from terraform 0.10.6 symbolic link handling does not work correctly anymore. Here you cannot use the direct variant link anymore. Instead run

    k8s/bin/prepare <variant name>

    to select the variant for your cluster project. If the variant has already been configured earlier, the argument can be omitted. This script generates a copy of the k8s module and replaces the indirect link variants/current by a direct link to the desired variant, instead of using the variant link in the cluster project. Whenever a new version of Kubify (this project) is used for the cluster project, this copy must be updated by calling prepare again.

  • Add the configuration values for your cluster (terraform.tfvars)

    For openstack this could look like this:

    os_user_name="<your user>"
os_password="<your password>"
os_auth_url="<your keystone auth url>"
os_tenant_name="<your tenant name>"
os_domain_name="<your openstack domain name>"
os_region="<your region>"
os_fip_pool_name="<your fip pool name>"

cluster_name="<your cluster name>"
cluster_type="<your cluster type>"

# DNS
dns = {
  dns_type = "route53"
  access_key="<route53 access key>"
  secret_key="<route53 secret key>"
  hosted_zone_id="<route53 hosted zone id>"
  hosted_zone_domain="<domain>"
}

# cluster size
master = {
  count=3
  flavor_name="medium_4_8"
}

worker = {
  count=3
  flavor_name="medium_2_4"
}

  • Setup the cluster Now you can call regular terraform commands for the project variant

    terraform init variant
terraform plan variant
terraform apply variant

Helper commands

  • Terraform commands There are shortcuts available including the get step during development:

    k8s/bin/plan
k8s/bin/apply
k8s/bin/tf <terraform command>

    This command sequence automatically runs the prepare step and the terraform get step, if required.

  • Access to master, worker and bastion nodes

    k8s/bin/master [<n> [<shell command to execute on master>]]
k8s/bin/worker [<n> [<shell command to execute on worker>]]

k8s/bin/master list   # list all IPs of VMs intended for master nodes
k8s/bin/worker list   # list all IPs of VMs intended for worker nodes

k8s/bin/bastion

  • Access to the api server The config file for kubectl can be found in gen/assets/auth/kubeconfig. Or just call

    • k8s/bin/k <options> # for kubectl
    • k8s/bin/ks <options> # for kubectl -n kube-system
    • `k8s/bin/kurl # for curl /

Quick Setup

Alternatively you can copy the project template https://github.com/gardener/kubify-openstack-template.git. Afterwards you set the originto your upstream git repository. Then continue with the configuration steps above.

It uses the same submodule, so don't forget to call

git submodule update --init --recursive

Configuration Settings

First of all there are required settings for every IaaS environment:

In addition there are various general settings that are independent of the chosen platform variant. Most of them have defaults that typically don't need to be changed.

The folloing variables are required for every cluster:

Name Meaning
cluster_name Name of the cluster. Used for DNS entries, the kubernetes cluster and for labelling the IaaS elements
cluster_type Type key of the cluster (for example: seed or infra). It ts used for the DNS entries and labeling the IaaS elements
dashboard_creds The credential file the kubernetes dashboard created by htpasswd. Unfortunately terraform does not support bcrypt up to now
master Settings for master nodes (see below)
worker Settimgs for worker nodes (see below)
bastion Settimgs for bastion VM (see below)

master and worker use the following common structure

Name Meaning
count Number of nodes (for master this should be an odd number, because it is also used to scale the cluster etcd service
flavor_name Optional: flavor used for the VM
image_name Optional: image used for the VM
assign_fips Optional: Always assign public IP to nodes
volume_size Optional: Size in GB of persistent volume for master (default: 20), should not be used for worker
update_mode Optional: Update mode for VMs
generation Optional: explicit node generation count to enforce recreation

For the bastion settings the following structure is used

Name Meaning
flavor_name Optional: flavor used for the VM
image_name Optional: image used for the VM
user_name Optional: user name of initial admin user of image

DNS configuration is done via the input map dns. It contains an entry dns_type to select the desired DNS provider and additional configuration entries required for that provider.

So far only route53 is supported as DNS provider. Therefore dedicated AWS credentials with appropriate permissions are required.

Configuration of the route53 DNS provider:

Name Meaning
access_key AWS access key for route53 access
secret_key AWS secret key for route53 access
hosted_zone_id Id of AWS hosted zone to use for the DNS entries
hosted_zone_domain Optional: domain name of hosted zone. Required if no base_domain or domain_name is configured for cluster. It is used to generate a unique domain name for clusters generated with kubify in this domain.

Etcd can be configured to create backups using the etcd operator. This can also be configured with the terraform project using the input map variable etcd_backup. The folowing backup modes are supported:

  • s3: AWS S3
  • pv: Persistent volume in cluster The default is pv. An appropriate kubernetes storage class is always created by the platform specific parts.

The mode is configured with the map entry storage_type. Other entries are used to configure the selected storage type.

For s3 AWS credentials must be configured:

Name Meaning
access_key AWS access key for S3 access
secret_key AWS secret key for S3 access

Besides those mandatory settings there are various optional settings.

Addons

Several addons can be chosen for optional deployment.

General settings
Name Meaning
ca_cert_pem Root certificate to be used for the cluster. By default generated for the dedicated cluster
ca_key_pem Key for the root certificate. Must always be configured together with ca_cert_pem
base_domain Base domain used for the cluster instead of generating it. The cluster name is still prepended
domain_name Domain name of the cluster. Sub domains are created for api, ingress,....
additional_domains List of additional domain names used for certificate generation
Node settings

These are otional settings for all kinds of nodes

Name Meaning
root_certs_file File containing additional root certificates to be installed on the nodes
dns_nameservers List of DNS servers to configure for the subnets and/or VMs
flavor_name Default flavor for all kinds of VMs
subnet_cidr IP range for node subnet (defaulted by IaaS modules)

It is possible to specify IaaS specific names (or search pattern for AWS). Additionally some mappings for preconfigured names come out of the box with this project:

  • ubuntu-16.04
  • coreos-1520.6.0 (not on Azure)
  • coreos-1548.3.0 (Azure)

Actual settings can be found here. With every new release more preconfigured settings are delivered with Kubify.

Name Meaning
use_bastion Use bastion host to avoid public node IPs if possible (depends on IAAS environment)
use_lbaas For testing purposes switch off load balancers
configure_additional_dns Create DNS entries for additional_domains
Kubernetes Configuration
Name Meaning
oidc_issuer_domain OIDC configuration for API server
oidc_issuer_subdomain OIDC configuration for API server
oidc_client_id OIDC configuration for API server, default: kube-kubectl
oidc_username_claim OIDC configuration for API server, default: email
oidc_groups_claim OIDC configuration for API server, default: groups
service_cidr Kubenetes cluster ip range (services) (default: 10.241.0.0/17)
pod_cidr Kubenetes pod ip range (default: 10.241.128.0/17)
VM update
Name Meaning
node_update_mode Standard node update mode (Roll, All or None)
update_kubelet handle kubelet update (default: false)

Additional node kind specific settings can be set using the master and worker configuration variables.

Recovery
Name Meaning
recover_cluster Enable cluster recovery mode if set to `true
etcd_backup_file Local path to the etcd backup file
Component versions

Versions are coming with the releases of this project. It is possible to override various versions, but there is no guarantee a selected combination of component versions works flawlessly (and with this terraform script) Actual versions are defined here.

Versions can be configured as member of a map variable versions. The following keys are supported:

Name Meaning
image_name image used for cluster VMs (master and nodes)
bastion_image_name image used for bastion VMs
kubernetes_version kubernetes version
dns_version DNS version
flannel_version flannel version
cni_version CNI version
etcd_version etcd version
etcd_operator_version etcd operator version
bootkube bootkube image name (default: quay.io/coreos/bootkube)
bootkube_version bootkube version
kubernetes_hyperkube image base name (default: gcr.io/google_containers/hyperkube)
kubernetes_hyperkube_patch image name suffix (default: _coreos.0)
nginx_version nginx version
lego_version lego version

Cluster Recovery

Store your etcd backup file somewhere in the filesystem and add the following settings to your terraform.tfvars file.

recover_cluster = "true"
etcd_backup_file= "<your etcd.backup file path>"

Now just re-run terraform apply variant (or try plan first).

This recreates the master volumes and nodes and then recreates the cluster using the backup as initial etcd content. All manual changes to your deployment of the standard components will be lost, because all standard components (not only the control plane) will be updated to the version configured in the terraform project.

Migrating to new Versions of the Kubify Project

Every new version of this project comes with a migration script migration.mig that is used by the command migrate. It is used to adapt terraform state files generated by former versions of this project before they can be used with the actual version. With this mechanism it is possible to change the structure of the terraform project for new versions without loosing cluster projects based on older versions. Nevertheless there might still be changes that cannot be migrated. The migration script then prompts an information about the latest commit, that can be used with the actual state version.

For this purpose the state structure used by this project is versioned (in modules/instance/version.tf). Running the project generates a file structure_version containing the actual version. Additionally the version is also contained in the state.auto.tfvars file.

The migration of the actual state file to the lastest structure version is done version by version until the actual version is reached.

The utility command apply, plan and tf implicitly do the state migration if required. If terraform is called manually the migration steps have be explicitly done by using the migrate utility command. It can always be called, because it checks if an action is required before touching the state file.

The migration command provides some utility functions used by the migration script. After defining those functions it just calls the migration script as regular shell script. The utility functions are based on the state manipulation sub commands of the terraform command.