Explain Docker Compose File https://github.com/stacksimplify/devops-real-world-project-implementation-on-aws/blob/main/04_Docker_Compose/docker-compose.yaml

🔷 1. Basic Info name: retail-sample

👉 Project name (used as prefix for containers, network, etc.)

🔷 2. Network networks: default: name: retail-sample_default

👉 Creates a custom Docker network

✔ All services talk using service name (DNS) Example:

catalog → accessible as http://catalog:8080 orders-db → orders-db:5432 🔷 3. Services (Main Part)

Each service = one container

🛒 3.1 cart service

👉 Handles shopping cart

Key points: Depends on: depends_on: carts-db: condition: service_healthy

✔ Waits until DB is healthy

Environment: RETAIL_CART_PERSISTENCE_PROVIDER=dynamodb RETAIL_CART_PERSISTENCE_DYNAMODB_ENDPOINT=http://carts-db:8000

✔ Uses DynamoDB (local container)

Security: cap_drop: all cap_add: NET_BIND_SERVICE read_only: true

✔ Minimal privileges (DevOps best practice)

Healthcheck: curl http://localhost:8080/actuator/health

✔ Docker checks if service is alive

🗄️ 3.2 carts-db image: amazon/dynamodb-local:1.20.0

👉 Local DynamoDB (no AWS needed)

✔ Used by cart service

📦 3.3 catalog

👉 Product listing service

Uses: RETAIL_CATALOG_PERSISTENCE_PROVIDER=mysql

✔ Connected to MySQL (MariaDB container)

🗄️ 3.4 catalog-db image: mariadb:10.9

👉 MySQL database

Env: MYSQL_DATABASE=catalogdb MYSQL_USER=catalog_user

✔ Creates DB + user automatically

💳 3.5 checkout

👉 Handles checkout process

Uses: RETAIL_CHECKOUT_PERSISTENCE_PROVIDER=redis

✔ Uses Redis (fast cache)

⚡ 3.6 checkout-redis image: redis:6.0-alpine

👉 In-memory DB for checkout

📑 3.7 orders

👉 Handles orders

Uses: PostgreSQL → DB RabbitMQ → messaging RETAIL_ORDERS_MESSAGING_PROVIDER=rabbitmq

✔ Event-driven architecture

🗄️ 3.8 orders-db image: postgres:16.1

👉 PostgreSQL DB

🐰 3.9 rabbitmq image: rabbitmq:3-management

👉 Message broker

✔ Used for async communication

🌐 3.10 ui (Frontend)

👉 Main entry point

Port mapping: ports:

• 8888:8080

✔ Access app on:

http://:8888 Depends on all services: cart, catalog, checkout, orders

✔ UI starts only when all backend services are healthy

🔷 4. Common Concepts (Important) 🔹 depends_on

✔ Controls startup order ✔ Waits for service health

🔹 healthcheck

✔ Docker checks service status ✔ Used for dependency readiness

🔹 environment

✔ Pass config to container ✔ DB connection, endpoints, etc.

🔹 restart: always

✔ Auto restart if container stops

🔹 read_only + tmpfs

✔ Security hardening ✔ Prevents filesystem modification

🔹 cap_drop / cap_add

✔ Linux capabilities control ✔ Reduce attack surface

🔥 How to run docker compose up -d Check: docker ps docker compose logs -f 🎯 Interview Answer (Short)

This is a microservices-based Docker Compose setup with multiple services like cart, catalog, orders, and UI. Each service uses its own database (DynamoDB, MySQL, Redis, PostgreSQL) and communicates over a shared network using service names. Health checks and depends_on ensure proper startup order, and security is enforced using read-only filesystems and dropped Linux capabilities.