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FAQ

Deployment Strategies

Which deployment strategies are supported by Flagger?

Flagger implements the following deployment strategies:

When should I use A/B testing instead of progressive traffic shifting?

For frontend applications that require session affinity, you should use HTTP headers or cookie match conditions to ensure a set of users will stay on the same version for the whole duration of the canary analysis.

Can I use Flagger to manage applications that live outside of a service mesh?

For applications that are not deployed on a service mesh, Flagger can orchestrate Blue/Green style deployments with Kubernetes L4 networking.

When can I use traffic mirroring?

Traffic mirroring can be used for Blue/Green deployment strategy or a pre-stage in a Canary release. Traffic mirroring will copy each incoming request, sending one request to the primary and one to the canary service. Mirroring should be used for requests that are idempotent or capable of being processed twice (once by the primary and once by the canary).

How to retry a failed release?

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

Deployment/DaemonSet PodSpec (metadata, 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

To retry a release you can add or change an annotation on the pod template:

apiVersion: apps/v1
kind: Deployment
spec:
  template:
    metadata:
      annotations:
        timestamp: "2020-03-10T14:24:48+0000"

How to change replicas for a deployment when not using HPA?

To change replicas for a deployment when not using HPA, you have to update the canary deployment with the desired replica count and trigger an analysis by annotating the template. After the analysis finishes, Flagger will promote the spec.replicas changes to the primary deployment.

Example:

apiVersion: apps/v1
kind: Deployment
spec:
  replicas: 4  #update replicas
  template:
    metadata:
      annotations:
        timestamp: "2022-02-10T14:24:48+0000" #add annotation to trigger analysis

Why is there a window of downtime during the canary initializing process when analysis is disabled?

A window of downtime is the intended behavior when the analysis is disabled. This allows instant rollback and also mimics the way a Kubernetes deployment initialization works. To avoid this, enable the analysis (skipAnalysis: false), wait for the initialization to finish, and disable it afterward (skipAnalysis: true).

How to disable cross namespace references?

Flagger by default can access resources across namespaces (AlertProivder, MetricProvider and Gloo Upsteream). If you’re in a multi-tenant environment and wish to disable this, you can do so through the no-cross-namespace-refs flag.

flagger \
  -no-cross-namespace-refs=true \
  ...

Kubernetes services

How is an application exposed inside the cluster?

Assuming the app name is podinfo, you can define a canary like:

apiVersion: flagger.app/v1beta1
kind: Canary
metadata:
  name: podinfo
  namespace: test
spec:
  targetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: podinfo
  service:
    # service name (optional)
    name: podinfo
    # ClusterIP port number (required)
    port: 9898
    # container port name or number
    targetPort: http
    # port name can be http or grpc (default http)
    portName: http

If the service.name is not specified, then targetRef.name is used for the apex domain and canary/primary services name prefix. You should treat the service name as an immutable field; changing its could result in routing conflicts.

Based on the canary spec service, Flagger generates the following Kubernetes ClusterIP service:

<service.name>.<namespace>.svc.cluster.local
selector app=<name>-primary
<service.name>-primary.<namespace>.svc.cluster.local
selector app=<name>-primary
<service.name>-canary.<namespace>.svc.cluster.local
selector app=<name>

This ensures that traffic coming from a namespace outside the mesh to podinfo.test:9898 will be routed to the latest stable release of your app.

apiVersion: v1
kind: Service
metadata:
  name: podinfo
spec:
  type: ClusterIP
  selector:
    app: podinfo-primary
  ports:
  - name: http
    port: 9898
    protocol: TCP
    targetPort: http
---
apiVersion: v1
kind: Service
metadata:
  name: podinfo-primary
spec:
  type: ClusterIP
  selector:
    app: podinfo-primary
  ports:
  - name: http
    port: 9898
    protocol: TCP
    targetPort: http
---
apiVersion: v1
kind: Service
metadata:
  name: podinfo-canary
spec:
  type: ClusterIP
  selector:
    app: podinfo
  ports:
  - name: http
    port: 9898
    protocol: TCP
    targetPort: http

The podinfo-canary.test:9898 address is available only during the canary analysis and can be used for conformance testing or load testing.

Multiple ports

My application listens on multiple ports. How can I expose them inside the cluster?

If port discovery is enabled, Flagger scans the deployment spec and extracts the containers ports excluding the port specified in the canary service and Envoy sidecar ports. These ports will be used when generating the ClusterIP services.

For a deployment that exposes two ports:

apiVersion: apps/v1
kind: Deployment
spec:
  template:
    metadata:
      annotations:
        prometheus.io/scrape: "true"
        prometheus.io/port: "9899"
    spec:
      containers:
      - name: app
        ports:
        - containerPort: 8080
        - containerPort: 9090

You can enable port discovery so that Prometheus will be able to reach port 9090 over mTLS:

apiVersion: flagger.app/v1beta1
kind: Canary
spec:
  service:
    # container port used for canary analysis
    port: 8080
    # port name can be http or grpc (default http)
    portName: http
    # add all the other container ports
    # to the ClusterIP services (default false)
    portDiscovery: true
    trafficPolicy:
      tls:
        mode: ISTIO_MUTUAL

Both port 8080 and 9090 will be added to the ClusterIP services.

Label selectors

What labels selectors are supported by Flagger?

The target deployment must have a single label selector in the format app: <DEPLOYMENT-NAME>:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: podinfo
spec:
  selector:
    matchLabels:
      app: podinfo
  template:
    metadata:
      labels:
        app: podinfo

Besides app, Flagger supports name and app.kubernetes.io/name selectors. If you use a different convention, you can specify your label with the -selector-labels flag. For example:

flagger \
  -selector-labels=service,name,app.kubernetes.io/name \
  ...

Is pod affinity and anti affinity supported?

Flagger will rewrite the first value in each match expression, defined in the target deployment’s pod anti-affinity and topology spread constraints, satisfying the following two requirements when creating, or updating, the primary deployment:

The key in the match expression must be one of the labels specified by the parameter selector-labels. The default labels are app,name,app.kubernetes.io/name.
The value must match the name of the target deployment.

The rewrite done by Flagger in these cases is to suffix the value with -primary. This rewrite can be used to spread the pods created by the canary and primary deployments across different availability zones.

Example target deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: podinfo
spec:
  selector:
    matchLabels:
      app: podinfo
  template:
    metadata:
      labels:
        app: podinfo
    spec:
      affinity:
        podAntiAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
          - weight: 100
            podAffinityTerm:
              labelSelector:
                matchExpressions:
                - key: app
                  operator: In
                  values:
                    - podinfo
              topologyKey: topology.kubernetes.io/zone

Example of generated primary deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: podinfo-primary
spec:
  selector:
    matchLabels:
      app: podinfo-primary
  template:
    metadata:
      labels:
        app: podinfo-primary
    spec:
      affinity:
        podAntiAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
          - weight: 100
            podAffinityTerm:
              labelSelector:
                matchExpressions:
                - key: app
                  operator: In
                  values:
                    - podinfo-primary
              topologyKey: topology.kubernetes.io/zone

It is also possible to use a different label than the app, name or app.kubernetes.io/name.

Anti affinity example(using a different label):

apiVersion: apps/v1
kind: Deployment
metadata:
  name: podinfo
spec:
  selector:
    matchLabels:
      app: podinfo
      affinity: podinfo
  template:
    metadata:
      labels:
        app: podinfo
        affinity: podinfo
    spec:
      affinity:
        podAntiAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
          - weight: 100
            podAffinityTerm:
              labelSelector:
                matchLabels:
                  affinity: podinfo
              topologyKey: topology.kubernetes.io/zone

Metrics

How does Flagger measure the request success rate and duration?

By default, Flagger measures the request success rate and duration using Prometheus queries.

HTTP requests success rate percentage

Spec:

  analysis:
    metrics:
    - name: request-success-rate
      # minimum req success rate (non 5xx responses)
      # percentage (0-100)
      thresholdRange:
        min: 99
      interval: 1m

Istio query:

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]
    )
)

Envoy query (App Mesh):

sum(
    rate(
        envoy_cluster_upstream_rq{
          kubernetes_namespace="$namespace",
          kubernetes_pod_name=~"$workload",
          envoy_response_code!~"5.*"
        }[$interval]
    )
)
/
sum(
    rate(
        envoy_cluster_upstream_rq{
          kubernetes_namespace="$namespace",
          kubernetes_pod_name=~"$workload"
        }[$interval]
    )
)

Envoy query (Contour and Gloo):

sum(
    rate(
        envoy_cluster_upstream_rq{
            envoy_cluster_name=~"$namespace-$workload",
            envoy_response_code!~"5.*"
        }[$interval]
    )
)
/
sum(
    rate(
        envoy_cluster_upstream_rq{
            envoy_cluster_name=~"$namespace-$workload",
        }[$interval]
    )
)

HTTP requests milliseconds duration P99

Spec:

  analysis:
    metrics:
    - name: request-duration
      # maximum req duration P99
      # milliseconds
      thresholdRange:
        max: 500
      interval: 1m

Istio query:

histogram_quantile(0.99,
  sum(
    irate(
      istio_request_duration_milliseconds_bucket{
        reporter="destination",
        destination_workload=~"$workload",
        destination_workload_namespace=~"$namespace"
      }[$interval]
    )
  ) by (le)
)

Envoy query (App Mesh, Contour and Gloo):

histogram_quantile(0.99,
  sum(
    irate(
      envoy_cluster_upstream_rq_time_bucket{
        kubernetes_pod_name=~"$workload",
        kubernetes_namespace=~"$namespace"
      }[$interval]
    )
  ) by (le)
)

Note that the metric interval should be lower or equal to the control loop interval.

Can I use custom metrics?

The analysis can be extended with metrics provided by Prometheus, Datadog, AWS CloudWatch, New Relic and Graphite. For more details on how custom metrics can be used, please read the metrics docs.

Istio Gateway API

If you’re using Istio with Gateway API, the Prometheus query needs to include reporter="source". For example, to calculate HTTP requests error percentage, the query would be:

100 - sum(
    rate(
        istio_requests_total{
          reporter="source",
          destination_workload_namespace=~"$namespace",
          destination_workload=~"$workload",
          response_code!~"5.*"
        }[$interval]
    )
)
/
sum(
    rate(
        istio_requests_total{
          reporter="source",
          destination_workload_namespace=~"$namespace",
          destination_workload=~"$workload"
        }[$interval]
    )
) * 100

Istio routing

How does Flagger interact with Istio?

Flagger creates an Istio Virtual Service and Destination Rules based on the Canary service spec. The service configuration lets you expose an app inside or outside the mesh. You can also define traffic policies, HTTP match conditions, URI rewrite rules, CORS policies, timeout and retries.

The following spec exposes the frontend workload inside the mesh on frontend.test.svc.cluster.local:9898 and outside the mesh on frontend.example.com. You’ll have to specify an Istio ingress gateway for external hosts.

apiVersion: flagger.app/v1beta1
kind: Canary
metadata:
  name: frontend
  namespace: test
spec:
  service:
    # container port
    port: 9898
    # service port name (optional, will default to "http")
    portName: http-frontend
    # Istio gateways (optional)
    gateways:
    - public-gateway.istio-system.svc.cluster.local
    - mesh
    # Istio virtual service host names (optional)
    hosts:
    - frontend.example.com
    # Istio traffic policy
    trafficPolicy:
      tls:
        # use ISTIO_MUTUAL when mTLS is enabled
        mode: DISABLE
    # HTTP match conditions (optional)
    match:
      - uri:
          prefix: /
    # HTTP rewrite (optional)
    rewrite:
      uri: /
    # Istio retry policy (optional)
    retries:
      attempts: 3
      perTryTimeout: 1s
      retryOn: "gateway-error,connect-failure,refused-stream"
    # Add headers (optional)
    headers:
      request:
        add:
          x-some-header: "value"
    # cross-origin resource sharing policy (optional)
    corsPolicy:
      allowOrigin:
        - example.com
      allowMethods:
        - GET
      allowCredentials: false
      allowHeaders:
        - x-some-header
      maxAge: 24h

For the above spec Flagger will generate the following virtual service:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: frontend
  namespace: test
  ownerReferences:
    - apiVersion: flagger.app/v1beta1
      blockOwnerDeletion: true
      controller: true
      kind: Canary
      name: podinfo
      uid: 3a4a40dd-3875-11e9-8e1d-42010a9c0fd1
spec:
  gateways:
    - public-gateway.istio-system.svc.cluster.local
    - mesh
  hosts:
    - frontend.example.com
    - frontend
  http:
  - corsPolicy:
      allowHeaders:
      - x-some-header
      allowMethods:
      - GET
      allowOrigin:
      - example.com
      maxAge: 24h
    headers:
      request:
        add:
          x-some-header: "value"
    match:
    - uri:
        prefix: /
    rewrite:
      uri: /
    route:
    - destination:
        host: podinfo-primary
      weight: 100
    - destination:
        host: podinfo-canary
      weight: 0
    retries:
      attempts: 3
      perTryTimeout: 1s
      retryOn: "gateway-error,connect-failure,refused-stream"

For each destination in the virtual service a rule is generated:

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: frontend-primary
  namespace: test
spec:
  host: frontend-primary
  trafficPolicy:
    tls:
      mode: DISABLE
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: frontend-canary
  namespace: test
spec:
  host: frontend-canary
  trafficPolicy:
    tls:
      mode: DISABLE

Flagger keeps in sync the virtual service and destination rules with the canary service spec. Any direct modification to the virtual service spec will be overwritten.

To expose a workload inside the mesh on http://backend.test.svc.cluster.local:9898, the service spec can contain only the container port and the traffic policy:

apiVersion: flagger.app/v1beta1
kind: Canary
metadata:
  name: backend
  namespace: test
spec:
  service:
    port: 9898
    trafficPolicy:
      tls:
        mode: DISABLE

Based on the above spec, Flagger will create several ClusterIP services like:

apiVersion: v1
kind: Service
metadata:
  name: backend-primary
  ownerReferences:
  - apiVersion: flagger.app/v1beta1
    blockOwnerDeletion: true
    controller: true
    kind: Canary
    name: backend
    uid: 2ca1a9c7-2ef6-11e9-bd01-42010a9c0145
spec:
  type: ClusterIP
  ports:
  - name: http
    port: 9898
    protocol: TCP
    targetPort: 9898
  selector:
    app: backend-primary

Flagger works for user facing apps exposed outside the cluster via an ingress gateway and for backend HTTP APIs that are accessible only from inside the mesh.

If Delegation is enabled, Flagger would generate Istio VirtualService without hosts and gateway, making the service compatible with Istio delegation.

apiVersion: flagger.app/v1beta1
kind: Canary
metadata:
  name: backend
  namespace: test
spec:
  service:
    delegation: true
    port: 9898
  targetRef:
    apiVersion: v1
    kind: Deployment
    name: podinfo
  analysis:
    interval: 15s
    threshold: 15
    maxWeight: 30
    stepWeight: 10

Based on the above spec, Flagger will create the following virtual service:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: backend
  namespace: test
  ownerReferences:
  - apiVersion: flagger.app/v1beta1
    blockOwnerDeletion: true
    controller: true
    kind: Canary
    name: backend
    uid: 58562662-5e10-4512-b269-2b789c1b30fe
spec:
  http:
  - route:
    - destination:
        host: podinfo-primary
      weight: 100
    - destination:
        host: podinfo-canary
      weight: 0

Therefore, the following virtual service forwards the traffic to /podinfo by the above delegate VirtualService.

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: frontend
  namespace: test
spec:
  gateways:
    - public-gateway.istio-system.svc.cluster.local
    - mesh
  hosts:
    - frontend.example.com
    - frontend
  http:
  - match:
    - uri:
        prefix: /podinfo
    rewrite:
      uri: /
    delegate:
      name: backend
      namespace: test

Note that pilot env PILOT_ENABLE_VIRTUAL_SERVICE_DELEGATE must also be set. For the use of Istio Delegation, you can refer to the documentation of Virtual Service and pilot environment variables.

Istio Ingress Gateway

How can I expose multiple canaries on the same external domain?

Assuming you have two apps – one that serves the main website and one that serves its REST API – you can define a canary object for each app as:

apiVersion: flagger.app/v1beta1
kind: Canary
metadata:
  name: website
spec:
  service:
    port: 8080
    gateways:
    - public-gateway.istio-system.svc.cluster.local
    hosts:
    - my-site.com
    match:
      - uri:
          prefix: /
    rewrite:
      uri: /
---
apiVersion: flagger.app/v1beta1
kind: Canary
metadata:
  name: webapi
spec:
  service:
    port: 8080
    gateways:
    - public-gateway.istio-system.svc.cluster.local
    hosts:
    - my-site.com
    match:
      - uri:
          prefix: /api
    rewrite:
      uri: /

Based on the above configuration, Flagger will create two virtual services bounded to the same ingress gateway and external host. Istio Pilot will merge the two services and the website rule will be moved to the end of the list in the merged configuration.

Note that host merging only works if the canaries are bounded to an ingress gateway other than the mesh gateway.

Istio Mutual TLS

How can I enable mTLS for a canary?

When deploying Istio with global mTLS enabled, you have to set the TLS mode to ISTIO_MUTUAL:

apiVersion: flagger.app/v1beta1
kind: Canary
spec:
  service:
    trafficPolicy:
      tls:
        mode: ISTIO_MUTUAL

If you run Istio in permissive mode, you can disable TLS:

apiVersion: flagger.app/v1beta1
kind: Canary
spec:
  service:
    trafficPolicy:
      tls:
        mode: DISABLE

If Flagger is outside of the mesh, how can it start the load test?

In order for Flagger to be able to call the load tester service from outside the mesh, you need to disable mTLS:

apiVersion: networking.istio.io/v1beta1
kind: DestinationRule
metadata:
  name: flagger-loadtester
  namespace: test
spec:
  host: "flagger-loadtester.test.svc.cluster.local"
  trafficPolicy:
    tls:
      mode: DISABLE
---
apiVersion: security.istio.io/v1beta1
kind: PeerAuthentication
metadata:
  name: flagger-loadtester
  namespace: test
spec:
  selector:
    matchLabels:
      app: flagger-loadtester
  mtls:
    mode: DISABLE

ExternalDNS

Can I use annotations?

Flagger propagates annotations (and labels) to all the generated apex, primary and canary objects. This allows using external-dns annotations.

You can configure Flagger to set annotations with:

spec:
  service:
    apex:
      annotations:
        external-dns.alpha.kubernetes.io/hostname: "mydomain.com"
    primary:
      annotations:
        external-dns.alpha.kubernetes.io/hostname: "primary.mydomain.com"
    canary:
      annotations:
        external-dns.alpha.kubernetes.io/hostname: "canary.mydomain.com"

Multiple sources and Istio

/!\ The apex annotations are added to both the generated Kubernetes Services and the generated Istio VirtualServices objects. If you have configured external-dns to use both sources, this will create conflicts!

    spec:
      containers:
        args:
        - --source=service              # choose only one
        - --source=istio-virtualservice # of these two

Checkout ExternalDNS documentation

Last modified 2022-11-17: update flagger docs to 1.25.0 (f9dffa4)