Docker Compose の利用

Docker Compose is a tool that helps you define and share multi-container applications. With Compose, you can create a YAML file to define the services and with a single command, you can spin everything up or tear it all down.

The big advantage of using Compose is you can define your application stack in a file, keep it at the root of your project repository (it's now version controlled), and easily enable someone else to contribute to your project. Someone would only need to clone your repository and start the app using Compose. In fact, you might see quite a few projects on GitHub/GitLab doing exactly this now.

Create the Compose file

In the getting-started-app directory, create a file named compose.yaml.

├── getting-started-app/
│ ├── Dockerfile
│ ├── compose.yaml
│ ├── node_modules/
│ ├── package.json
│ ├── spec/
│ ├── src/
│ └── yarn.lock

Define the app service

In part 6, you used the following command to start the application service.

$ docker run -dp 127.0.0.1:3000:3000 \
  -w /app -v "$(pwd):/app" \
  --network todo-app \
  -e MYSQL_HOST=mysql \
  -e MYSQL_USER=root \
  -e MYSQL_PASSWORD=secret \
  -e MYSQL_DB=todos \
  node:18-alpine \
  sh -c "yarn install && yarn run dev"

You'll now define this service in the compose.yaml file.

Open compose.yaml in a text or code editor, and start by defining the name and image of the first service (or container) you want to run as part of your application. The name will automatically become a network alias, which will be useful when defining your MySQL service.
services: app: image: node:18-alpine
Typically, you will see command close to the image definition, although there is no requirement on ordering. Add the command to your compose.yaml file.
services: app: image: node:18-alpine command: sh -c "yarn install && yarn run dev"

Now migrate the -p 127.0.0.1:3000:3000 part of the command by defining the ports for the service.

services:
  app:
    image: node:18-alpine
    command: sh -c "yarn install && yarn run dev"
    ports:
      - 127.0.0.1:3000:3000

Next, migrate both the working directory (-w /app) and the volume mapping (-v "$(pwd):/app") by using the working_dir and volumes definitions.
One advantage of Docker Compose volume definitions is you can use relative paths from the current directory.
services: app: image: node:18-alpine command: sh -c "yarn install && yarn run dev" ports: - 127.0.0.1:3000:3000 working_dir: /app volumes: - ./:/app

Finally, you need to migrate the environment variable definitions using the environment key.

services:
  app:
    image: node:18-alpine
    command: sh -c "yarn install && yarn run dev"
    ports:
      - 127.0.0.1:3000:3000
    working_dir: /app
    volumes:
      - ./:/app
    environment:
      MYSQL_HOST: mysql
      MYSQL_USER: root
      MYSQL_PASSWORD: secret
      MYSQL_DB: todos

Define the MySQL service

Now, it's time to define the MySQL service. The command that you used for that container was the following:

$ docker run -d \
  --network todo-app --network-alias mysql \
  -v todo-mysql-data:/var/lib/mysql \
  -e MYSQL_ROOT_PASSWORD=secret \
  -e MYSQL_DATABASE=todos \
  mysql:8.0

First define the new service and name it mysql so it automatically gets the network alias. Also specify the image to use as well.
services: app: # The app service definition mysql: image: mysql:8.0
Next, define the volume mapping. When you ran the container with docker run, Docker created the named volume automatically. However, that doesn't happen when running with Compose. You need to define the volume in the top-level volumes: section and then specify the mountpoint in the service config. By simply providing only the volume name, the default options are used.
services: app: # The app service definition mysql: image: mysql:8.0 volumes: - todo-mysql-data:/var/lib/mysql volumes: todo-mysql-data:

Finally, you need to specify the environment variables.

services:
  app:
    # The app service definition
  mysql:
    image: mysql:8.0
    volumes:
      - todo-mysql-data:/var/lib/mysql
    environment:
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_DATABASE: todos

volumes:
  todo-mysql-data:

At this point, your complete compose.yaml should look like this:

services:
  app:
    image: node:18-alpine
    command: sh -c "yarn install && yarn run dev"
    ports:
      - 127.0.0.1:3000:3000
    working_dir: /app
    volumes:
      - ./:/app
    environment:
      MYSQL_HOST: mysql
      MYSQL_USER: root
      MYSQL_PASSWORD: secret
      MYSQL_DB: todos

  mysql:
    image: mysql:8.0
    volumes:
      - todo-mysql-data:/var/lib/mysql
    environment:
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_DATABASE: todos

volumes:
  todo-mysql-data:

Run the application stack

Now that you have your compose.yaml file, you can start your application.

Make sure no other copies of the containers are running first. Use docker ps to list the containers and docker rm -f <ids> to remove them.
Start up the application stack using the docker compose up command. Add the -d flag to run everything in the background.
$ docker compose up -d
When you run the previous command, you should see output like the following:
Creating network "app_default" with the default driver Creating volume "app_todo-mysql-data" with default driver Creating app_app_1 ... done Creating app_mysql_1 ... done
You'll notice that Docker Compose created the volume as well as a network. By default, Docker Compose automatically creates a network specifically for the application stack (which is why you didn't define one in the Compose file).
Look at the logs using the docker compose logs -f command. You'll see the logs from each of the services interleaved into a single stream. This is incredibly useful when you want to watch for timing-related issues. The -f flag follows the log, so will give you live output as it's generated.
If you have run the command already, you'll see output that looks like this:
mysql_1 | 2019-10-03T03:07:16.083639Z 0 [Note] mysqld: ready for connections. mysql_1 | Version: '8.0.31' socket: '/var/run/mysqld/mysqld.sock' port: 3306 MySQL Community Server (GPL) app_1 | Connected to mysql db at host mysql app_1 | Listening on port 3000
The service name is displayed at the beginning of the line (often colored) to help distinguish messages. If you want to view the logs for a specific service, you can add the service name to the end of the logs command (for example, docker compose logs -f app).
At this point, you should be able to open your app in your browser on http://localhost:3000 and see it running.

See the app stack in Docker Desktop Dashboard

If you look at the Docker Desktop Dashboard, you'll see that there is a group named getting-started-app. This is the project name from Docker Compose and used to group the containers together. By default, the project name is simply the name of the directory that the compose.yaml was located in.

If you expand the stack, you'll see the two containers you defined in the Compose file. The names are also a little more descriptive, as they follow the pattern of <service-name>-<replica-number>. So, it's very easy to quickly see what container is your app and which container is the mysql database.

Tear it all down

When you're ready to tear it all down, simply run docker compose down or hit the trash can on the Docker Desktop Dashboard for the entire app. The containers will stop and the network will be removed.

警告
By default, named volumes in your compose file are not removed when you run docker compose down. If you want to remove the volumes, you need to add the --volumes flag.
The Docker Desktop Dashboard does not remove volumes when you delete the app stack.

Summary

In this section, you learned about Docker Compose and how it helps you simplify the way you define and share multi-service applications.

Related information:

Next steps

Next, you'll learn about a few best practices you can use to improve your Dockerfile.

Image-building best practices