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Docker Compose networking

Goal:​

Understand Docker Compose networking and how to define custom networks for our services.

Step 1: Defining a custom network​

If we dont specify a network, docker will automatically create a default network for our application.

However, we can define a custom network in the docker-compose.yml file.

networks:
  spring-mysql:
    driver: bridge

Then, we can attach our services to this network:

services:
  db:
    networks:
      - spring-mysql

  app:
    networks:
      - spring-mysql

Step 2: Removing port exposure​

Since the services are connected over a custom network, we can remove the database exposure to the host machine, as it is no longer needed. Update the docker-compose.yml file to remove the ports section from the db service:

services:
  db:
    ports:
      - "3306"
    networks:
      - spring-mysql

  app:
    ports:
      - "127.0.0.1:8080:8080"
    networks:
      - spring-mysql

Even though the database is isolated inside the container, it is still accessible to the app container over the custom network.

Step 3: Compose everything​

Run docker compose up -d to start the services in detached mode.

Step 4: Inspect the network​

We can inspect the network, to show which containers are in the network.

First list the networks:

docker network ls

There should be a network named docker-spring_spring-mysql, try to inspect it, by running:

docker network inspect docker-spring_spring-mysql

Here you can see the containers that are connected to the network (under the "Containers" section).

Step 5: Tear everything down​

Tear it all down:

docker compose down -v

And do a (nuclear 💣) cleanup:

docker system prune -f