Skip to main content

What is Docker Compose?

  • Compose is a tool for defining and running multi-container Docker applications.
  • With Compose, you use a YAML file to configure your application’s services.
    • Then, with a single command, you create and start all the services from your configuration.
    • More examples here
version: "3.7" 
services: 
	... 
volumes: 
	... 
networks: 
	...

Docker-compose's Three Steps​

  1. Define your app's environments with a Dockerfile
  2. Define the services that make up your app in docker-compose.yml so they can be run together in an isolated environment.
  3. Run docker compose up to start and run your apps,
version: '3.8'

services:
 notes:
  build: .   #path to where the docker-file is ex: ./dir/src/
  ports:
   - 8000:8000
   - 9229:9229
  environment:
   - SERVER_PORT=8000
   - CONNECTIONSTRING=mongodb://mongo:27017/notes
  volumes:
   - ./:/app

 mongo:
  image: mongo:4.2.8
  ports:
   - 27017:27017
  volumes:
   - mongodb:/data/db
   - mongodb_config:/data/configdb

volumes:
 mongodb:
 mongodb_config:

Declaring the Dependencies​

  • We need to create a dependency chain between our services, so that some services get loaded before (and unloaded after) other ones.
  • We can achieve this result through the depends_on keyword
services:
  kafka:
    image: wurstmeister/kafka:2.11-0.11.0.3
    depends_on:
      - zookeeper
    ...
  zookeeper:
    image: wurstmeister/zookeeper
    ...
#First zookeeper starts then kafka starts

We should be aware, however, that Compose will not wait for the zookeeper service to finish loading before starting the kafka service: it will simply wait for it to start.

Docker-compose Commands​

Build​

  • Builds images in the docker-compose.yml file. The job of the build command is to get the images ready to create containers,
  • So if a service is using the prebuilt image, it will skip this service.
docker-compose build

Start​

  • Starts existing containers for a service.
docker-compose start

Restart​

  • Restarts all stopped and running services.
docker-compose restart

Stop​

  • This command stops the running containers of specified services.
docker-compose stop

Up​

  • It builds the images if they are not located locally and starts the containers.
  • If images are already built, it will fork the container directly.
  • If there are existing containers for a service, and the service’s configuration or image was changed after the container’s creation, 
    • docker-compose up picks up the changes by stopping and recreating the containers (preserving mounted volumes).
docker-compose up

docker-compose up -d  #-d detached /background

docker-compose up -d --build
#build the images
#And then start the containers

PS​

  • This command list all the containers in the current docker-compose file. They can then either be running or stopped.
docker-compose ps

Down​

  • Stops containers and removes containers, networks, volumes, and images created by up.
    • Networks and volumes defined as external are never removed.
docker-compose down