Blue/Green Deployment with Nginx

Simple blue/green deployment setup using Docker Compose and Nginx for zero-downtime failover.

Prerequisites

• Docker installed
• Docker Compose installed
• Internet connection (to pull images)

Quick Start

1. Clone the repository

   git clone <your-repo-url>
   cd <repo-name>

2. Set up environment variables

   cp .env.example .env
   # Edit .env if needed (default values should work)

3. Run the deployment script

   chmod +x deploy.sh
   ./deploy.sh

The script will:

• Pull Docker images from Docker Hub
• Set up Nginx configuration
• Start all services (nginx, blue app, green app)

4. Verify it's running

   curl http://localhost:8080/version

Endpoints

• Main Service (via Nginx): http://localhost:8080
• Blue App (direct): http://localhost:8081
• Green App (direct): http://localhost:8082

Available Routes

• GET /version - Returns app version and pool info
• GET /healthz - Health check endpoint
• POST /chaos/start?mode=error - Simulate failure on the app
• POST /chaos/stop - Stop simulated failure

Testing Failover

1. Check current active pool (should be Blue)

   curl -i http://localhost:8080/version
   # Look for X-App-Pool: blue header

2. Trigger chaos on Blue

   curl -X POST http://localhost:8081/chaos/start?mode=error

3. Test automatic failover to Green

   curl -i http://localhost:8080/version
   # Should now show X-App-Pool: green header
   # All requests should return 200 OK

4. Stop chaos

   curl -X POST http://localhost:8081/chaos/stop

Configuration

All configuration is in .env file:

BLUE_IMAGE=<docker-hub-image-for-blue>
GREEN_IMAGE=<docker-hub-image-for-green>
ACTIVE_POOL=blue
RELEASE_ID_BLUE=v1.0.0-blue
RELEASE_ID_GREEN=v1.0.0-green

Files in This Repo

• docker-compose.yml - Service orchestration
• nginx.conf.template - Nginx configuration template
• .env.example - Environment variables template
• deploy.sh - Automated deployment script
• README.md - This file
• DECISION.md - Implementation decisions (optional)

Stopping the Services

docker-compose down

Troubleshooting

Services not starting?

• Check Docker is running: docker ps
• Check logs: docker-compose logs

Can't connect to localhost:8080?

• Verify nginx container is running: docker-compose ps
• Check if port 8080 is already in use: lsof -i :8080

Failover not working?

• Check nginx logs: docker-compose logs nginx
• Verify both apps are healthy: curl http://localhost:8081/healthz

Architecture

Client Request
    ↓
Nginx (localhost:8080)
    ├─→ Blue App (localhost:8081) [Primary]
    └─→ Green App (localhost:8082) [Backup]

When Blue fails, Nginx automatically retries the request to Green within the same client request.

Notes

• Zero downtime failover is automatic
• Health checks run continuously
• Failed requests are retried to backup automatically
• All upstream headers are preserved# deploy_docker