Running containers with docker compose

What is docker compose?

Docker compose is a tool that simplifies the way we define and run containers. Especially when having multiple containers, this tool can streamline the process for us.

For detailed information about this tool, have a look at the Docker Compose official documentation.

How to write a docker compose file

In order to instruct docker compose what containers we want to run and how to run it (e.g: what ports we want to expose), we need to create a configuration file.

This configuration file has yaml format and by default, when running the tool, it will search for a file called docker-compose.yaml or compose.yaml.

Let’s look at a service configuration in the docker compose file for the reference application. The file looks like this:

services:
  app:
    build: .
    ports:
      - "8080:8080"

What does this mean?

The example above means that we configured a service called “app” that can be built based on a Dockerfile in the current directory, and we mapped the container port 8080 to the host port 8080 so that we can access it on localhost. The purpose of this is to then be able to run the container in a simple way.

How to run the java app container with docker compose

• Now that we have configured the ports, we can simply run this: docker compose up app
• To verify that the app is running, check the status endpoint: http://localhost:8080/private/status.
• To check what containers are running with docker compose, run: docker compose ps.

Note: There are other settings we can configure here, a full list can be found in the compose file reference.