Docker Compose

  • Docker Compose is a tool that allows you to define and manage multi-container docker applications with a single command. 
  • Docker Compose uses a YAML file to configure the application's services, networks, and volumes, enabling you to define and manage the entire stack in one place.
Example: Create a docker-compose.yml file and defines the services, networks, and volumes your application requires. 

version: '3'
services:
  web:
    image: nginx
    ports:
      - "80:80"
  mydb:
    image: postgres
    environment:
      POSTGRES_PASSWORD: test123

Here, 
- version 3 is docker-compose file version so use all commands in this file as per version 3
- services are containers
  
  • Create and run services (services' containers) defined in the docker-compose.yml file

       docker-compose up

       Create and run services in the background 

       docker-compose up -d

       You can specify an alternate docker compose file rather than default docker-  compose.yml with 'f' option 

       docker-compose -f docker-compose.prod.yml up

  • Stop and remove resources like containers, networks, and volumes created by docker-compose up command.

       docker-compose down 

  • Stop the running services without removing them
       docker-compose stop

       Stop specific service 
       docker-compose stop mydb

  • Force stop the running services
       docker-compose kill 

  • Start the stopped services
       docker-compose start

  • Restart the services
       docker-compose restart
 
       Restart specific service 
       docker-compose restart mydb 

  • Remove stopped services
       docker-compose rm

  • Restart services
       docker-compose restart

  • Pull service images
       docker-compose pull

  • Push service images
       docker-compose push

  • Display the logs from services.
       docker-compose logs 
         
       You can use -f option to follow the logs in real-time
       docker-compose logs -f 

  • Scale the "mydb" service to 3 instances
       docker-compose up --scale mydb=3 

  • Execute a command inside a running service
       docker-compose exec web ls / 

  • List images
       docker-compose images 

  • List running services
       docker-compose ps 

  • Pause/Unpause services
       docker-compose pause
       docker-compose unpause 

  • Validate and view YAML file
       docker-compose config 

  • List all docker-compose commands

       docker-compose --help


  • Build or rebuild the Docker images defined in a docker-compose.yml file
docker-compose build
 
Please note docker skips building pre-built images like postgre etc if its there in your docker-compose file. So you can't build an image using above docker-compose.yml file in which we are using pre-built images nginx and postgre 

Example: Building a docker image according to the Dockerfile.  

mkdir my_workspace
cd my_workspace

Step1: Create index.html
</html><body>Hello, Docker Compose!</body></html> 
 
Step2: Create Dockerfile
FROM nginx:alpine
COPY index.html /usr/share/nginx/html/index.html  

Step3: Create docker-compose.yml file
version: '3'
services:
  web:
    build: .
    ports:
      - "8000:80"
  
👉 Here we are saying that docker should build an image from the Dockerfile located in the current directory (.)
  
Step4: Building a docker image
docker-compose build

Step5: After building the image, you can start the container with
docker-compose up 

you can access container with URL http://localhost:8000 in your web browser. 

 

  • Install docker-compose tool

sudo curl -L "https://github.com/docker/compose/releases/download/1.29.2/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose

sudo chmod +x /usr/local/bin/docker-compose

sudo docker-compose --version

 

Docker Compose tool simplifies working with multi-container docker applications, making it a powerful tool for both development and production environments.

Whatever things we do with a bunch of docker commands like creating images, containers, volume, network, scaling and stuff those all are simplified with docker-compose

Common Use Cases,
Microservices: Easily manage multiple microservices within a single application.
Local Development: Spin up local development environments that closely mirror production.
Testing: Use Docker Compose to run integration tests in isolated environments.
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