Deployment Patterns (Blue-Green, Canary, Rolling)

# Blue Deployment (current live — v1)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-blue
  labels:
    app: myapp
    version: blue
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
      version: blue
  template:
    metadata:
      labels:
        app: myapp
        version: blue
    spec:
      containers:
      - name: app
        image: myapp:v1.0.0   # Current stable version
        ports:
        - containerPort: 8080
---
# Green Deployment (new version — v2)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-green
  labels:
    app: myapp
    version: green
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
      version: green
  template:
    metadata:
      labels:
        app: myapp
        version: green
    spec:
      containers:
      - name: app
        image: myapp:v2.0.0   # New version (deployed silently)
        ports:
        - containerPort: 8080
---
# Service — Traffic কোথায় যাবেন সেটা নিয়ন্ত্রণ করে
apiVersion: v1
kind: Service
metadata:
  name: app-service
spec:
  selector:
    app: myapp
    version: blue   # ← শুধু এই একটা line change করলেনই switch!
    # version: green  ← Green-এ switch করতে এটা uncomment করুন
  ports:
  - port: 80
    targetPort: 8080

# Stable deployment (19 replicas = 95% traffic)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-stable
spec:
  replicas: 19          # 95% of total pods
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
        track: stable
    spec:
      containers:
      - name: app
        image: myapp:v1.0.0
---
# Canary deployment (1 replica = 5% traffic)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-canary
spec:
  replicas: 1           # 5% of total pods
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
        track: canary
    spec:
      containers:
      - name: app
        image: myapp:v2.0.0
---
# Single Service — উভয় deployment-এ route করে (label: app=myapp)
apiVersion: v1
kind: Service
metadata:
  name: app-service
spec:
  selector:
    app: myapp    # উভয় stable + canary pods match করে
  ports:
  - port: 80
    targetPort: 8080
# Traffic split proportional to replica count:
# 19 stable + 1 canary = 20 total → 95% / 5% split

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  replicas: 4
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1         # Extra pods: temporarily 5 pods চলতে পারে
      maxUnavailable: 1   # একবারে max ১টা pod down থাকতে পারে
                          # maxUnavailable: 0 → zero downtime guarantee
                          # maxSurge: 25%  → percentage ব্যবহার করা যায়
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: app
        image: myapp:v2.0.0    # ← শুধু এটা পরিবর্তন করলেনই rolling update শুরু
        readinessProbe:         # নতুন pod ready না হলে পুরনো pod নামাবে না
          httpGet:
            path: /healthz
            port: 8080
          initialDelaySeconds: 5
          periodSeconds: 3
        livenessProbe:
          httpGet:
            path: /healthz
            port: 8080
          initialDelaySeconds: 15
          periodSeconds: 10

// Feature Flag Service — TypeScript implementation
interface FeatureFlag {
    name: string;
    enabled: boolean;
    rolloutPercentage: number;   // 0-100: কতজন user দেখবেন
    allowedUserIds?: string[];   // Specific users (beta testers)
    allowedGroups?: string[];    // User groups ('premium', 'internal')
}

class FeatureFlagService {
    private flags: Map<string, FeatureFlag>;

    constructor() {
        // LaunchDarkly / ConfigCat / custom config থেকে load হয়
        this.flags = new Map([
            ['new-checkout-flow', {
                name: 'new-checkout-flow',
                enabled: true,
                rolloutPercentage: 5,       // মাত্র ৫% users দেখবেন
                allowedUserIds: ['user_beta_001', 'user_beta_002'],
            }],
            ['ai-recommendations', {
                name: 'ai-recommendations',
                enabled: false,             // সম্পূর্ণ বন্ধ
                rolloutPercentage: 0,
            }],
            ['dark-mode-v2', {
                name: 'dark-mode-v2',
                enabled: true,
                rolloutPercentage: 100,     // সবাই পাচ্ছে
            }],
        ]);
    }

    // User-এর জন্য flag enabled কিনা check করুন
    isEnabled(flagName: string, userId: string): boolean {
        const flag = this.flags.get(flagName);
        if (!flag || !flag.enabled) return false;

        // Specific users override
        if (flag.allowedUserIds?.includes(userId)) return true;

        // Percentage-based rollout: userId hash করে consistent bucketing
        const bucket = this.getUserBucket(userId);
        return bucket < flag.rolloutPercentage;
    }

    // User ID থেকে consistent 0-100 bucket বের করুন
    private getUserBucket(userId: string): number {
        let hash = 0;
        for (const char of userId) {
            hash = (hash * 31 + char.charCodeAt(0)) % 100;
        }
        return hash;
    }

    // Runtime-এ flag update করুন (deploy ছাড়াই!)
    updateFlag(flagName: string, updates: Partial<FeatureFlag>): void {
        const existing = this.flags.get(flagName);
        if (existing) {
            this.flags.set(flagName, { ...existing, ...updates });
        }
    }
}

// Usage in application code:
const flags = new FeatureFlagService();

async function handleCheckout(userId: string, cart: Cart) {
    if (flags.isEnabled('new-checkout-flow', userId)) {
        // নতুন checkout flow (৫% users)
        return await newCheckoutService.process(cart);
    } else {
        // পুরনো checkout flow (৯৫% users)
        return await legacyCheckoutService.process(cart);
    }
}