Automated canary deployments with Flagger

Flagger is a Kubernetes operator that automates the promotion of canary deployments using Istio routing for traffic shifting and Prometheus metrics for canary analysis.

Install Flagger

Deploy Flagger in the istio-system namespace using Helm:

# add the Helm repository
helm repo add flagger https://flagger.app

# install or upgrade
helm upgrade -i flagger flagger/flagger \
--namespace=istio-system \
--set metricsServer=http://prometheus.istio-system:9090

Flagger is compatible with Kubernetes >1.11.0 and Istio >1.0.0.

Flagger takes a Kubernetes deployment and optionally a horizontal pod autoscaler (HPA) and creates a series of objects (Kubernetes deployments, ClusterIP services and Istio virtual services) to drive the canary analysis and promotion.

A canary deployment is triggered by changes in any of the following objects:

Deployment PodSpec (container image, command, ports, env, resources, etc)
ConfigMaps mounted as volumes or mapped to environment variables
Secrets mounted as volumes or mapped to environment variables

Gated canary promotion stages:

scan for canary deployments
check Istio virtual service routes are mapped to primary and canary ClusterIP services
check primary and canary deployments status
- halt advancement if a rolling update is underway
- halt advancement if pods are unhealthy
increase canary traffic weight percentage from 0% to 5% (step weight)
call webhooks and check results
check canary HTTP request success rate and latency
- halt advancement if any metric is under the specified threshold
- increment the failed checks counter
check if the number of failed checks reached the threshold
- route all traffic to primary
- scale to zero the canary deployment and mark it as failed
- wait for the canary deployment to be updated and start over
increase canary traffic weight by 5% (step weight) till it reaches 50% (max weight)
- halt advancement while canary request success rate is under the threshold
- halt advancement while canary request duration P99 is over the threshold
- halt advancement if the primary or canary deployment becomes unhealthy
- halt advancement while canary deployment is being scaled up/down by HPA
promote canary to primary
- copy ConfigMaps and Secrets from canary to primary
- copy canary deployment spec template over primary
wait for primary rolling update to finish
- halt advancement if pods are unhealthy
route all traffic to primary
scale to zero the canary deployment
mark rollout as finished
wait for the canary deployment to be updated and start over

You can change the canary analysis max weight and the step weight percentage in the Flagger's custom resource.

Automated canary analysis and promotion

Create a test namespace with Istio sidecar injection enabled:

export REPO=https://raw.githubusercontent.com/weaveworks/flagger/master

kubectl apply -f ${REPO}/artifacts/namespaces/test.yaml

Create a deployment and a horizontal pod autoscaler:

kubectl apply -f ${REPO}/artifacts/canaries/deployment.yaml
kubectl apply -f ${REPO}/artifacts/canaries/hpa.yaml

Deploy the load testing service to generate traffic during the canary analysis:

kubectl -n test apply -f ${REPO}/artifacts/loadtester/deployment.yaml
kubectl -n test apply -f ${REPO}/artifacts/loadtester/service.yaml

Create a canary custom resource (replace example.com with your own domain):

apiVersion: flagger.app/v1alpha3
kind: Canary
metadata:
  name: podinfo
  namespace: test
spec:
  # deployment reference
  targetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: podinfo
  # the maximum time in seconds for the canary deployment
  # to make progress before it is rollback (default 600s)
  progressDeadlineSeconds: 60
  # HPA reference (optional)
  autoscalerRef:
    apiVersion: autoscaling/v2beta1
    kind: HorizontalPodAutoscaler
    name: podinfo
  service:
    # container port
    port: 9898
    trafficPolicy:
      tls:
        # use ISTIO_MUTUAL when mTLS is enabled
        mode: DISABLE
    # Istio gateways (optional)
    gateways:
    - public-gateway.istio-system.svc.cluster.local
    - mesh
    # Istio virtual service host names (optional)
    hosts:
    - app.example.com
  canaryAnalysis:
    # schedule interval (default 60s)
    interval: 1m
    # max number of failed metric checks before rollback
    threshold: 5
    # max traffic percentage routed to canary
    # percentage (0-100)
    maxWeight: 50
    # canary increment step
    # percentage (0-100)
    stepWeight: 10
    metrics:
    - name: request-success-rate
      # minimum req success rate (non 5xx responses)
      # percentage (0-100)
      threshold: 99
      interval: 1m
    - name: request-duration
      # maximum req duration P99
      # milliseconds
      threshold: 500
      interval: 30s
    # generate traffic during analysis
    webhooks:
      - name: load-test
        url: http://flagger-loadtester.test/
        timeout: 5s
        metadata:
          cmd: "hey -z 1m -q 10 -c 2 http://podinfo-canary.test:9898/"

Save the above resource as podinfo-canary.yaml and then apply it:

kubectl apply -f ./podinfo-canary.yaml

After a couple of seconds Flagger will create the canary objects:

# applied 
deployment.apps/podinfo
horizontalpodautoscaler.autoscaling/podinfo
canary.flagger.app/podinfo

# generated 
deployment.apps/podinfo-primary
horizontalpodautoscaler.autoscaling/podinfo-primary
service/podinfo
service/podinfo-canary
service/podinfo-primary
virtualservice.networking.istio.io/podinfo

Trigger a canary deployment by updating the container image:

kubectl -n test set image deployment/podinfo \
podinfod=quay.io/stefanprodan/podinfo:1.4.1

Flagger detects that the deployment revision changed and starts a new rollout:

kubectl -n test describe canary/podinfo

Status:
  Canary Revision:  19871136
  Failed Checks:    0
  State:            finished
Events:
  Type     Reason  Age   From     Message
  ----     ------  ----  ----     -------
  Normal   Synced  3m    flagger  New revision detected podinfo.test
  Normal   Synced  3m    flagger  Scaling up podinfo.test
  Warning  Synced  3m    flagger  Waiting for podinfo.test rollout to finish: 0 of 1 updated replicas are available
  Normal   Synced  3m    flagger  Advance podinfo.test canary weight 5
  Normal   Synced  3m    flagger  Advance podinfo.test canary weight 10
  Normal   Synced  3m    flagger  Advance podinfo.test canary weight 15
  Normal   Synced  2m    flagger  Advance podinfo.test canary weight 20
  Normal   Synced  2m    flagger  Advance podinfo.test canary weight 25
  Normal   Synced  1m    flagger  Advance podinfo.test canary weight 30
  Normal   Synced  1m    flagger  Advance podinfo.test canary weight 35
  Normal   Synced  55s   flagger  Advance podinfo.test canary weight 40
  Normal   Synced  45s   flagger  Advance podinfo.test canary weight 45
  Normal   Synced  35s   flagger  Advance podinfo.test canary weight 50
  Normal   Synced  25s   flagger  Copying podinfo.test template spec to podinfo-primary.test
  Warning  Synced  15s   flagger  Waiting for podinfo-primary.test rollout to finish: 1 of 2 updated replicas are available
  Normal   Synced  5s    flagger  Promotion completed! Scaling down podinfo.test

Note that if you apply new changes to the deployment during the canary analysis, Flagger will restart the analysis.

You can monitor all canaries with:

watch kubectl get canaries --all-namespaces

NAMESPACE   NAME      STATUS        WEIGHT   LASTTRANSITIONTIME
test        podinfo   Progressing   15       2019-01-16T14:05:07Z
prod        frontend  Succeeded     0        2019-01-15T16:15:07Z
prod        backend   Failed        0        2019-01-14T17:05:07Z

Automated rollback

During the canary analysis you can generate HTTP 500 errors and high latency to test if Flagger pauses the rollout.

Create a tester pod and exec into it:

kubectl -n test run tester --image=quay.io/stefanprodan/podinfo:1.2.1 -- ./podinfo --port=9898
kubectl -n test exec -it tester-xx-xx sh

Generate HTTP 500 errors:

watch curl http://podinfo-canary:9898/status/500

Generate latency:

watch curl http://podinfo-canary:9898/delay/1

When the number of failed checks reaches the canary analysis threshold, the traffic is routed back to the primary, the canary is scaled to zero and the rollout is marked as failed.

kubectl -n test describe canary/podinfo

Status:
  Canary Revision:  16695041
  Failed Checks:    10
  State:            failed
Events:
  Type     Reason  Age   From     Message
  ----     ------  ----  ----     -------
  Normal   Synced  3m    flagger  Starting canary deployment for podinfo.test
  Normal   Synced  3m    flagger  Advance podinfo.test canary weight 5
  Normal   Synced  3m    flagger  Advance podinfo.test canary weight 10
  Normal   Synced  3m    flagger  Advance podinfo.test canary weight 15
  Normal   Synced  3m    flagger  Halt podinfo.test advancement success rate 69.17% < 99%
  Normal   Synced  2m    flagger  Halt podinfo.test advancement success rate 61.39% < 99%
  Normal   Synced  2m    flagger  Halt podinfo.test advancement success rate 55.06% < 99%
  Normal   Synced  2m    flagger  Halt podinfo.test advancement success rate 47.00% < 99%
  Normal   Synced  2m    flagger  (combined from similar events): Halt podinfo.test advancement success rate 38.08% < 99%
  Warning  Synced  1m    flagger  Rolling back podinfo.test failed checks threshold reached 10
  Warning  Synced  1m    flagger  Canary failed! Scaling down podinfo.test

Monitoring

Flagger comes with a Grafana dashboard made for canary analysis.

Install Grafana with Helm:

helm upgrade -i flagger-grafana flagger/grafana \
--namespace=istio-system \
--set url=http://prometheus.istio-system:9090

The dashboard shows the RED and USE metrics for the primary and canary workloads:

The canary errors and latency spikes have been recorded as Kubernetes events and logged by Flagger in json format:

kubectl -n istio-system logs deployment/flagger --tail=100 | jq .msg

Starting canary deployment for podinfo.test
Advance podinfo.test canary weight 5
Advance podinfo.test canary weight 10
Advance podinfo.test canary weight 15
Advance podinfo.test canary weight 20
Advance podinfo.test canary weight 25
Advance podinfo.test canary weight 30
Advance podinfo.test canary weight 35
Halt podinfo.test advancement success rate 98.69% < 99%
Advance podinfo.test canary weight 40
Halt podinfo.test advancement request duration 1.515s > 500ms
Advance podinfo.test canary weight 45
Advance podinfo.test canary weight 50
Copying podinfo.test template spec to podinfo-primary.test
Halt podinfo-primary.test advancement waiting for rollout to finish: 1 old replicas are pending termination
Scaling down podinfo.test
Promotion completed! podinfo.test

Alerting

Flagger can be configured to send Slack notifications:

helm upgrade -i flagger flagger/flagger \
--namespace=istio-system \
--set slack.url=https://hooks.slack.com/services/YOUR/SLACK/WEBHOOK \
--set slack.channel=general \
--set slack.user=flagger

Once configured with a Slack incoming webhook, Flagger will post messages when a canary deployment has been initialized, when a new revision has been detected and if the canary analysis failed or succeeded.

A canary deployment will be rolled back if the progress deadline exceeded or if the analysis reached the maximum number of failed checks:

Besides Slack, you can use Alertmanager to trigger alerts when a canary deployment failed:

  - alert: canary_rollback
    expr: flagger_canary_status > 1
    for: 1m
    labels:
      severity: warning
    annotations:
      summary: "Canary failed"
      description: "Workload {{ $labels.name }} namespace {{ $labels.namespace }}"

Next: A/B Testing with Helm

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Automated canary deployments with Flagger

Install Flagger

Automated canary analysis and promotion

Automated rollback

Monitoring

Alerting