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Canary deployment is a strategy for releasing new features, where the update is gradually rolled out to a small subset of users, and if no issues arise, it is then spread to the entire audience.

Main steps:

1. Deploy the canary group: The new version of the application is deployed on a small subset of servers or users.
2. Monitoring: Careful monitoring of metrics (errors, performance, user behavior) for the canary group.
3. Expansion or rollback:
   • If monitoring shows success, the deployment gradually expands to a larger group of users.
   • If problems are detected, the deployment is rolled back for the canary group, protecting the main user base.

Advantages:

• Risk minimization: Problems affect a small subset of users.
• Quick rollback: Easy to revert to the previous version.
• Testing in real conditions: Evaluation of the new functionality's behavior under real load.

Disadvantages:

• Infrastructure complexity: Support for multiple versions of the application simultaneously is required.
• Traffic management: Mechanisms are needed to route traffic to different versions.
• Data analysis: Efficient collection and analysis of metrics are necessary.

Example implementation in Kubernetes:

// Deployment for v1
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app-v1
spec:
  replicas: 10 // Main count
  selector:
    matchLabels:
      app: my-app
      version: v1
  template:
    metadata:
      labels:
        app: my-app
        version: v1
    spec:
      containers:
      - name: my-app
        image: my-registry/my-app:v1

---

// Deployment for canary v2
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app-v2-canary
spec:
  replicas: 1 // Canary group
  selector:
    matchLabels:
      app: my-app
      version: v2
  template:
    metadata:
      labels:
        app: my-app
        version: v2
    spec:
      containers:
      - name: my-app
        image: my-registry/my-app:v2

---

// Service for traffic routing (using selectors)
apiVersion: v1
kind: Service
metadata:
  name: my-app-service
spec:
  selector:
    app: my-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080

Traffic distribution between v1 and v2 is managed using Ingress controllers (e.g., Nginx Ingress, Istio) with weighted traffic distribution capabilities.