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Flagger - Istio progressive delivery Kubernetes operator
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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. The project is currently in experimental phase and it is expected that breaking changes to the API will be made in the upcoming releases.
Install
Before installing Flagger make sure you have Istio setup up with Prometheus enabled. If you are new to Istio you can follow my Istio service mesh walk-through .
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 \ --set controlLoopInterval=1m
Flagger is compatible with Kubernetes >1.10.0 and Istio >1.0.0.
Usage
Flagger takes a Kubernetes deployment and creates a series of objects (Kubernetes deployments , ClusterIP services and Istio virtual services ) to drive the canary analysis and promotion.
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)
- 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 (revision bump) 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 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 (revision bump) and start over
You can change the canary analysis max weight and the step weight percentage in the Flagger's custom resource.
For a deployment named podinfo , a canary promotion can be defined using Flagger's custom resource:
apiVersion: flagger.app/v1alpha1 kind: Canary metadata: name: podinfo namespace: test spec: # deployment reference targetRef: apiVersion: apps/v1 kind: Deployment name: podinfo # hpa reference (optional) autoscalerRef: apiVersion: autoscaling/v2beta1 kind: HorizontalPodAutoscaler name: podinfo service: # container port port: 9898 # Istio gateways (optional) gateways: - public-gateway.istio-system.svc.cluster.local # Istio virtual service host names (optional) hosts: - app.istio.weavedx.com canaryAnalysis: # 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: istio_requests_total # minimum req success rate (non 5xx responses) # percentage (0-100) threshold: 99 interval: 1m - name: istio_request_duration_seconds_bucket # maximum req duration P99 # milliseconds threshold: 500 interval: 30s
The canary analysis is using the following promql queries:
HTTP requests success rate percentage
sum( rate( istio_requests_total{ reporter="destination", destination_workload_namespace=~"$namespace", destination_workload=~"$workload", response_code!~"5.*" }[$interval] ) ) / sum( rate( istio_requests_total{ reporter="destination", destination_workload_namespace=~"$namespace", destination_workload=~"$workload" }[$interval] ) )
HTTP requests milliseconds duration P99
histogram_quantile(0.99, sum( irate( istio_request_duration_seconds_bucket{ reporter="destination", destination_workload=~"$workload", destination_workload_namespace=~"$namespace" }[$interval] ) ) by (le) )
Automated canary analysis, promotions and rollbacks
Create a test namespace with Istio sidecar injection enabled:
export REPO=https://raw.githubusercontent.com/stefanprodan/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
Create a canary promotion custom resource (replace the Istio gateway and the internet domain with your own):
kubectl apply -f ${REPO}/artifacts/canaries/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:1.2.1
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
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
Flagger exposes Prometheus metrics that can be used to determine the canary analysis status and the destination weight values:
# Canaries total gauge flagger_canary_total{namespace="test"} 1 # Canary promotion last known status gauge # 0 - running, 1 - successful, 2 - failed flagger_canary_status{name="podinfo" namespace="test"} 1 # Canary traffic weight gauge flagger_canary_weight{workload="podinfo-primary" namespace="test"} 95 flagger_canary_weight{workload="podinfo" namespace="test"} 5 # Seconds spent performing canary analysis histogram flagger_canary_duration_seconds_bucket{name="podinfo",namespace="test",le="10"} 6 flagger_canary_duration_seconds_bucket{name="podinfo",namespace="test",le="+Inf"} 6 flagger_canary_duration_seconds_sum{name="podinfo",namespace="test"} 17.3561329 flagger_canary_duration_seconds_count{name="podinfo",namespace="test"} 6
Roadmap
- Extend the canary analysis and promotion to other types than Kubernetes deployments such as Flux Helm releases or OpenFaaS functions
- Extend the validation mechanism to support other metrics than HTTP success rate and latency
- Add support for comparing the canary metrics to the primary ones and do the validation based on the derivation between the two
- Alerting: trigger Alertmanager on successful or failed promotions
- Reporting: publish canary analysis results to Slack/Jira/etc
Contributing
Flagger is Apache 2.0 licensed and accepts contributions via GitHub pull requests.
When submitting bug reports please include as much details as possible:
- which Flagger version
- which Flagger CRD version
- which Kubernetes/Istio version
- what configuration (canary, virtual service and workloads definitions)
- what happened (Flagger, Istio Pilot and Proxy logs)
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