Blue-Green Deployment: How to update your app without a second of downtime

services:
app-blue:
image: myapp:${TAG:-latest}
build:
profiles: [blue]
restart: unless-stopped
labels:
- "traefik.enable=true" # or use nginx

app-green:
image: myapp:${TAG:-latest}
build:
profiles: ["green"]
restart: unless-stopped

upstream backend {
    server app-blue:3000;  # меняем на app-green при switch
}

server {
    listen 80;
    location / {
        proxy_pass http://backend;
        proxy_set_header Host $host;
    }
}

#!/bin/bash
ACTIVE=$(cat /var/run/active-slot.txt 2>/dev/null || echo "blue")
NEW_SLOT=$( [ "$ACTIVE" = "blue" ] && echo "green" || echo "blue")

docker compose --profile $NEW_SLOT up -d --build
sleep 10  # health check
curl -f http://localhost/health || exit 1

echo "$NEW_SLOT" > /var/run/active-slot.txt
sed -i "s/app-$ACTIVE/app-$NEW_SLOT/" /etc/nginx/nginx.conf
nginx -s reload

docker compose --profile $ACTIVE stop
echo "✅ Переключили на $NEW_SLOT!"

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-blue
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
      color: blue
  template:
    metadata:
      labels:
        app: myapp
        color: blue
    spec:
      containers:
      - name: app
        image: myapp:v1
        readinessProbe:
          httpGet:
            path: /health
            port: 3000

apiVersion: v1
kind: Service
metadata:
  name: myapp-service
spec:
  selector:
    app: myapp
    color: blue   # ← меняешь на green и apply
  ports:
  - port: 80
    targetPort: 3000

kubectl apply -f green-deployment.yaml
#wait ready
kubectl patch service myapp-service -p '{"spec":{"selector":{"color:"green"}}'
Blue can be removed or left as standby

resource "kubernetes_deployment" "blue" { ... color = "blue" ... }
resource "kubernetes_deployment" "green" { ... color = "green" ... }

resource "kubernetes_service" "app" {
  spec {
    selector = {
      color = var.active_color  # "blue" или "green" — меняешь в variables.tf
    }
  }
}

name: Blue-Green Deploy
on: [push]
jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v4
    - name: Build & Push
      run: docker build -t myapp:${{ github.sha }} && docker push ...
    - name: Deploy to inactive
      run: ssh user@server "./deploy-to-inactive.sh ${{ github.sha }}"
    - name: Tests
      run: curl -f https://staging.myapp.com/health
    - name: Switch
      run: ssh user@server "./switch.sh"

" Create a complete ready-to-use file set for blue-green deployment of my FastAPI (Python) application on Ubuntu VPS.
- docker-compose.yml with blue/green profiles
nginx.conf with dynamic upstream
deploy.sh with health checks, logging, rollback
- GitHub Actions workflow
Instructions for first launch and daily use.
Make it as reliable as possible, with zero-downtime and comments in Russian

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