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Frequently asked questions

Deployment Strategies

Which deployment strategies are supported by Flagger?

Flagger can run automated application analysis, promotion and rollback for the following deployment strategies:

Canary (progressive traffic shifting)
- Istio, Linkerd, App Mesh, NGINX, Gloo
A/B Testing (HTTP headers and cookies traffic routing)
- Istio, NGINX
Blue/Green (traffic switch)
- Kubernetes CNI

For Canary deployments and A/B testing you'll need a Layer 7 traffic management solution like a service mesh or an ingress controller. For Blue/Green deployments no service mesh or ingress controller is required.

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 cookies match conditions to ensure a set of users will stay on the same version for the whole duration of the canary analysis. A/B testing is supported by Istio and NGINX only.

Istio example:

  canaryAnalysis:
    # schedule interval (default 60s)
    interval: 1m
    # total number of iterations
    iterations: 10
    # max number of failed iterations before rollback
    threshold: 2
    # canary match condition
    match:
      - headers:
          x-canary:
            regex: ".*insider.*"
      - headers:
          cookie:
            regex: "^(.*?;)?(canary=always)(;.*)?$"

NGINX example:

  canaryAnalysis:
    interval: 1m
    threshold: 10
    iterations: 2
    match:
      - headers:
          x-canary:
            exact: "insider"
      - headers:
          cookie:
            exact: "canary"

Note that the NGINX ingress controller supports only exact matching for a single header and the cookie value is set to always.

The above configurations will route users with the x-canary header or canary cookie to the canary instance during analysis:

curl -H 'X-Canary: insider' http://app.example.com
curl -b 'canary=always' http://app.example.com

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.

Blue/Green example:

apiVersion: flagger.app/v1alpha3
kind: Canary
spec:
  provider: kubernetes
  canaryAnalysis:
    interval: 30s
    threshold: 2
    iterations: 10       
    metrics:
      - name: request-success-rate
        threshold: 99
        interval: 1m
      - name: request-duration
        threshold: 500
        interval: 30s
    webhooks:
      - name: load-test
        url: http://flagger-loadtester.test/
        timeout: 5s
        metadata:
          type: cmd
          cmd: "hey -z 1m -q 10 -c 2 http://podinfo-canary.test:9898/"

The above configuration will run an analysis for five minutes. Flagger starts the load test for the canary service (green version) and checks the Prometheus metrics every 30 seconds. If the analysis result is positive, Flagger will promote the canary (green version) to primary (blue version).

When can I use traffic mirroring?

Traffic Mirroring is a pre-stage in a Canary (progressive traffic shifting) or Blue/Green deployment strategy. Traffic mirroring will copy each incoming request, sending one request to the primary and one to the canary service. The response from the primary is sent back to the user. The response from the canary is discarded. Metrics are collected on both requests so that the deployment will only proceed if the canary metrics are healthy.

Mirroring is supported by Istio only.

In Istio, mirrored requests have -shadow appended to the Host (HTTP) or Authority (HTTP/2) header; for example requests to podinfo.test that are mirrored will be reported in telemetry with a destination host podinfo.test-shadow.

Mirroring must only be used for requests that are idempotent or capable of being processed twice (once by the primary and once by the canary). Reads are idempotent. Before using mirroring on requests that may be writes, you should consider what will happen if a write is duplicated and handled by the primary and canary.

To use mirroring, set spec.canaryAnalysis.mirror to true. Example for traffic shifting:

apiVersion: flagger.app/v1alpha3
kind: Canary
spec:
  provider: istio
  canaryAnalysis:
    interval: 30s
    mirror: true
    stepWeight: 20
    maxWeight: 50
    metrics:
    - interval: 29s
      name: request-success-rate
      threshold: 99
    - interval: 29s
      name: request-duration
      threshold: 500

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/v1alpha3
kind: Canary
metadata:
  name: podinfo
  namespace: test
spec:
  targetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: podinfo
  service:
    # container port (required)
    port: 9898
    # port name can be http or grpc (default http)
    portName: http

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

<targetRef.name>.<namespace>.svc.cluster.local
selector app=<name>-primary
<targetRef.name>-primary.<namespace>.svc.cluster.local
selector app=<name>-primary
<targetRef.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/v1alpha3
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.

Is pod affinity and anti affinity supported?

For pod affinity to work you need to use a different label than the app, name or app.kubernetes.io/name.

Anti affinity example:

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: kubernetes.io/hostname

Istio Ingress Gateway

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

Assuming you have two apps, one that servers the main website and one that serves the REST API. For each app you can define a canary object as:

apiVersion: flagger.app/v1alpha3
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/v1alpha3
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 a 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/v1alpha3
kind: Canary
spec:
  service:
    trafficPolicy:
      tls:
        mode: ISTIO_MUTUAL

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

apiVersion: flagger.app/v1alpha3
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 on port 80:

apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: flagger-loadtester
  namespace: test
spec:
  host: "flagger-loadtester.test.svc.cluster.local"
  trafficPolicy:
    tls:
      mode: DISABLE
---
apiVersion: authentication.istio.io/v1alpha1
kind: Policy
metadata:
  name: flagger-loadtester
  namespace: test
spec:
  targets:
  - name: flagger-loadtester
    ports:
    - number: 80

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