Docker Compose

We can create multiple containers(eg: go, postgres) from single file using docker compose. Each container(services, networks, and volumes) have 1 entry inside this file
Then, with a single command, you create and start all the services from your configuration file
Docker Compose will create and manage one container per service, as recommended by docker
Services can be scaled up (except for stateful services like databases)

Examples

Container-1(Golang app), Container-2(postgres DB)

docker-compose.yml

$ cat docker-compose.yml

version: '3.8'      #latest stable version that supports all modern Docker features

services:           # Defines the containers that will be created
  postgres:
    image: postgres:latest                      # Uses official Postgres image
    container_name: postgres                    # Explicit container name
    environment:                                # Environment variables
      POSTGRES_USER: youruser                   # Database username
      POSTGRES_PASSWORD: yourpassword           # Database password
      POSTGRES_DB: yourdb                       # Default database name
    ports:
      - "5432:5432"                             # Maps host:container ports
    volumes:
      - postgres_data:/var/lib/postgresql/data  # Persistent storage
    networks:
      - go-postgres-net                         # Attaches to precreated network
    healthcheck:                                # Checks if DB is ready
      test: ["CMD-SHELL", "pg_isready -U youruser -d yourdb"]
      interval: 5s
      timeout: 5s
      retries: 5

  app:
    build: .                                    # Builds from Dockerfile in current directory
    container_name: go-app
    ports:
      - "8080:8080"                             # Exposes app port
    environment:                                # DB connection vars
      DB_HOST: postgres                         # Uses service name as hostname
      DB_USER: youruser
      DB_PASSWORD: yourpassword
      DB_NAME: yourdb
      DB_PORT: 5432
    depends_on:                                 # Startup order
      postgres:
        condition: service_healthy              # Waits until DB is ready
    networks:
      - go-postgres-net                         # Same network as DB

volumes:
  postgres_data:                                # Named volume for DB persistence

networks:
  go-postgres-net:
    external: true                              # Uses our pre-created network
        

Create containers

// Build or rebuild services. Forces a rebuild of images (even if they exist)
$ docker-compose build

// Start containers in background. starts all services in the compose file
// -d: background
$ docker-compose up -d

// Show status of containers
$ docker-compose ps
NAME              IMAGE           COMMAND                  SERVICE   CREATED         STATUS                  PORTS
go-server-app-1   go-server-app   "./main"                 app       2 seconds ago   Up Less than a second   0.0.0.0:8080->8080/tcp
go-server-db-1    postgres:16     "docker-entrypoint.s…"   db        32 hours ago    Up Less than a second   0.0.0.0:5432->5432/tcp

// Remove data stored in persistant volume. if you want to rebuild your database
# docker volume rm go-server_db_data 

// Stop and Delete containers,networks
$ docker-compose down