Feat: Add Support for Cookie Attributes in Session Affinity

[renatovassaomb]

Summary

Adding support for specifying all cookie attributes to Session Affinity except Expires, which doesn't look like it would be useful.

Fixes #1527

Changes

• Updated Istio router to support all cookie attributes when using session affinity.
• Updated Gateway API (v1 and v1beta1) routers to support all cookie attributes when using session affinity.

Testing

1. Init workloads

bash test/workloads/init.sh

2. Create Canary resource

apiVersion: flagger.app/v1beta1
kind: Canary
metadata:
  name: podinfo
  namespace: test
spec:
  targetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: podinfo
  progressDeadlineSeconds: 60
  service:
    port: 9898
    portDiscovery: true
  skipAnalysis: false
  analysis:
    interval: 15s
    threshold: 15
    maxWeight: 30
    stepWeight: 10
    sessionAffinity:
      cookieName: my-cookie
      domain: flagger.app
      httpOnly: true
      maxAge: 1200
      partitioned: true
      path: /app
      sameSite: Strict
      secure: true
    webhooks:
      - name: load-test
        url: http://flagger-loadtester.test/
        timeout: 5s
        metadata:
          type: cmd
          cmd: "hey -z 10m -q 10 -c 2 http://podinfo.test:9898/"
          logCmdOutput: "true"

4. Trigger canary release

kubectl -n test set image deployment/podinfo podinfod=ghcr.io/stefanprodan/podinfo:6.0.1 

5. Wait for canary to advance and check VirtualService routes

kubectl get vs -n test podinfo -o yaml 

apiVersion: networking.istio.io/v1beta1
kind: VirtualService
metadata:
  annotations:
    helm.toolkit.fluxcd.io/driftDetection: disabled
    kustomize.toolkit.fluxcd.io/reconcile: disabled
  creationTimestamp: "2025-09-11T18:38:19Z"
  generation: 3
  name: podinfo
  namespace: test
  ownerReferences:
  - apiVersion: flagger.app/v1beta1
    blockOwnerDeletion: true
    controller: true
    kind: Canary
    name: podinfo
    uid: fa160025-6579-4133-a6a5-6d5600ea9e6b
  resourceVersion: "21157"
  uid: ecd965b5-ab72-4cba-87d0-0204fd283136
spec:
  gateways:
  - mesh
  hosts:
  - podinfo
  http:
  - match:
    - headers:
        Cookie:
          regex: .*my-cookie.*PpzTnjuFDL.*
    name: sticky-route
    route:
    - destination:
        host: podinfo-primary
      weight: 0
    - destination:
        host: podinfo-canary
      weight: 100
  - route:
    - destination:
        host: podinfo-primary
      weight: 90
    - destination:
        host: podinfo-canary
      headers:
        response:
          add:
            Set-Cookie: my-cookie=PpzTnjuFDL; Max-Age=1200; Domain=flagger.app; HttpOnly;
              Partitioned; Path=/app; SameSite=Strict; Secure
      weight: 10

References

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Set-Cookie#attributes

[renatovassaomb]

@stefanprodan @aryan9600 Any thoughts?

[stefanprodan]

Can you please update the docs with all new fields here: https://docs.flagger.app/usage/deployment-strategies#canary-release-with-session-affinity

The source is here: https://github.com/fluxcd/flagger/blob/main/docs/gitbook/usage/deployment-strategies.md#configuring-stickiness-for-primary-deployment

[codecov-commenter]

Codecov Report

❌ Patch coverage is 17.24138% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 28.91%. Comparing base (12ee6cb) to head (fab4540).
⚠️ Report is 35 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/apis/flagger/v1beta1/canary.go	0.00%	24 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1826       +/-   ##
===========================================
- Coverage   39.44%   28.91%   -10.54%     
===========================================
  Files         287      287               
  Lines       22706    22909      +203     
===========================================
- Hits         8956     6623     -2333     
- Misses      12777    15561     +2784     
+ Partials      973      725      -248     

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[renatovassaomb]

Thanks for the review @stefanprodan, updated docs with new functionality.

[stefanprodan]

LGTM

Thanks @renatovassaomb