flagger

Flagger

Overview

Flagger automates progressive delivery for Kubernetes workloads. It gradually shifts traffic to a new version while measuring metrics and running conformance tests. Supports canary releases (weighted traffic), A/B testing (header/cookie routing), and blue/green deployments (instant switch or mirroring).

CRDs: Canary (flagger.app/v1beta1), MetricTemplate, AlertProvider.

Latest: chart 1.43.0, app v1.43.0 (Apr 2026).

Architecture

User creates/updates Canary resource
  → Flagger creates:
    - <name>-primary Deployment (stable version)
    - <name>-canary Deployment (new version)
    - <name> ClusterIP service (routes to primary)
    - <name>-primary ClusterIP service (stable)
    - <name>-canary ClusterIP service (new)
    - Mesh/Ingress routing objects (if mesh provider set)
  → Analysis loop:
    1. Increment traffic to canary (stepWeight)
    2. Run webhooks (pre-rollout, rollout, post-rollout)
    3. Check metrics (success rate, duration, custom)
    4. If all pass → promote canary to primary
    5. If threshold exceeded → rollback

CRD: Canary

apiVersion: flagger.app/v1beta1, kind: Canary

Minimal Example (Kubernetes CNI — no mesh)

apiVersion: flagger.app/v1beta1
kind: Canary
metadata:
  name: myapp
  namespace: prod
spec:
  provider: kubernetes    # No service mesh (uses ClusterIP + pod labels)
  targetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: myapp
  service:
    port: 9898
    portDiscovery: true
  analysis:
    interval: 1m
    threshold: 5
    iterations: 10        # Used for blue/green with no mesh provider
    metrics:
      - name: request-success-rate
        thresholdRange:
          min: 99
        interval: 1m
    webhooks:
      - name: load-test
        type: rollout
        url: http://flagger-loadtester.test/
        metadata:
          cmd: "hey -z 1m -q 10 http://myapp-canary.prod:9898/"

CanarySpec Fields

Field	Required	Description
provider	Yes	Traffic provider: kubernetes, istio, linkerd, nginx, contour, gloo, traefik, gatewayapi:v1, apisix, kuma, knative, skipper, osm, smi:v1alpha2, appmesh:v1beta2
targetRef	Yes	Target Deployment reference
autoscalerRef	No	HPA reference (copied to canary)
service	Yes	Service spec (port, portName, targetPort, hosts, gatewayRefs, match, rewrite, timeout, headers, etc.)
suspend	No	Suspend all canary runs
progressDeadlineSeconds	No	Max time for canary progress before rollback (default 600)
skipAnalysis	No	Promote without analysis (default false)