コンテナー化データベースの利用

Using a local containerized database offers flexibility and ease of setup, letting you mirror production environments closely without the overhead of traditional database installations. Docker simplifies this process, enabling you to deploy, manage, and scale databases in isolated containers with just a few commands.

このガイドでは以下について学びます。

• ローカルでのコンテナー化データベースの実行
• コンテナー化データベースへのシェルアクセス
• ホストからのコンテナー化データベースへの接続
• 別コンテナーからのコンテナー化データベースへの接続
• ボリューム内のデータベースデータの保存
• カスタマイズしたデータベースイメージのビルド
• Docker Compose を利用したデータベース実行

このガイドでは例として MySQL イメージを用います。 ただしその考え方は他のデータベースイメージにも適用することができます。

前提条件

このガイドの作業を進めるには Docker をすでにインストールしていることが必要です。 Docker のインストールについては Docker の入手 を参照してください。

ローカルでのコンテナー化データベースの実行

MySQL、PostgreSQL、MongoDB といった人気のデータベースシステムについては、そのほとんどが Docker Hub 上に Docker 公式イメージがあります。 そういったイメージはベストプラクティスを実現するものとして提供されており、最新機能やセキュリティアップデートが行われたものを利用することができます。 作業を進めるには Docker Hub にアクセスして、利用したいデータベースを検索します。 検索された各ページには、そのコンテナーを起動する手順、カスタマイズ方法、必要に応じたデータベース設定方法が詳細に示されています。 このガイドに示す MySQ についての情報は Docker Hub の MySQL イメージ ページを参照してください。

データベースコンテナーを起動するには Docker Desktop GUI か CLI を利用します。

$ docker run --name my-mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -e MYSQL_DATABASE=mydb -d mysql:latest

コンテナー化データベースへのシェルアクセス

Docker コンテナー内部でデータベースを起動したら、データベースの管理、コマンド実行、管理タスクの実現のため、データベースにアクセスするシェルの実行が必要になってきます。 Docker ではこれを行う簡単な方法として docker exec コマンドを提供しています。 またグラフィカルインターフェースを好むのであれば Docker Desktop GUI を利用することもできます。

データベースコンテナーをまだ起動していない場合は ローカルでのコンテナー化データベースの実行 を参照してください。

$ docker exec -it my-mysql bash

コンテナーの端末にアクセスできたら、あとはコンテナー内で利用可能なツール類は何でも利用できます。 以下に示す例では、コンテナー内の mysql を使ってデータベースの一覧を表示しています。

# mysql -u root -p
Enter password: my-secret-pw

mysql> SHOW DATABASES;

+--------------------+
| Database           |
+--------------------+
| information_schema |
| mydb               |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

ホストからのコンテナー化データベースへの接続

コンテナー化したデータベースにホストから接続するには、コンテナー内部のポートとホストマシン上のポートをマッピングする必要があります。 そのプロセスを実現することで、コンテナー内にあるデータベースはホストマシンのネットワークからアクセス可能となります。 MySQL の場合、デフォルトのポートは 3306 です。 このポートを公開すれば、ホストマシン上にあるさまざまなデータベース管理ツールやアプリケーションが MySQL データベースとやり取りできるようになります。

作業を進めるにあたっては、本ガイドを通じて実行させてきた以前のコンテナーは削除してください。 コンテナーを停止させ削除するには、以下のいずれかを行います。

• In a terminal, run docker rm --force my-mysql to remove the container named my-mysql.
• Or, in the Docker Desktop Dashboard, select the Delete icon next to your container in the Containers view.

Next, you can use either the Docker Desktop GUI or CLI to run the container with the port mapped.

$ docker run -p 3307:3306 --name my-mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -e MYSQL_DATABASE=mydb -d mysql:latest

$ docker ps

CONTAINER ID   IMAGE          COMMAND                  CREATED          STATUS          PORTS                               NAMES
6eb776cfd73c   mysql:latest   "docker-entrypoint.s…"   17 minutes ago   Up 17 minutes   33060/tcp, 0.0.0.0:3307->3306/tcp   my-mysql

At this point, any application running on your host can access the MySQL service in the container at localhost:3307.

Connect to a containerized database from another container

Connecting to a containerized database from another container is a common scenario in microservices architecture and during development processes. Docker's networking capabilities make it easy to establish this connection without having to expose the database to the host network. This is achieved by placing both the database container and the container that needs to access it on the same Docker network.

Before you begin, you must remove any containers you previously ran for this guide. To stop and remove a container, either:

• 端末から docker remove --force my-mysql を実行して my-mysql という名前のコンテナーを削除します。
• または Docker Desktop Dashboard の Containers (コンテナー) 画面にて、対象コンテナーの横にある Delete (削除) アイコンをクリックします。

To create a network and run containers on it:

1. Run the following command to create a Docker network named my-network.

   $ docker network create my-network
   

2. Run your database container and specify the network using the --network option. This runs the container on the my-network network.

   $ docker run --name my-mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -e MYSQL_DATABASE=mydb --network my-network -d mysql:latest
   

3. Run your other containers and specify the network using the --network option. For this example, you'll run a phpMyAdmin container that can connect to your database.

   1. Run a phpMyAdmin container. Use the --network option to specify the network, the -p option to let you access the container from your host machine, and the -e option to specify a required environment variable for this image.

      $ docker run --name my-phpmyadmin -d --network my-network -p 8080:80 -e PMA_HOST=my-mysql phpmyadmin
      

4. Verify that the containers can communicate. For this example, you'll access phpMyAdmin and verify that it connects to the database.

   1. Open http://localhost:8080 to access your phpMyAdmin container.
   2. Log in using root as the username and my-secret-pw as the password. You should connect to the MySQL server and see your database listed.

At this point, any application running on your my-network container network can access the MySQL service in the container at my-mysql:3306.

Persist database data in a volume

Persisting database data in a Docker volume is necessary for ensuring that your data survives container restarts and removals. A Docker volume lets you store database files outside the container's writable layer, making it possible to upgrade the container, switch bases, and share data without losing it. Here’s how you can attach a volume to your database container using either the Docker CLI or the Docker Desktop GUI.

Before you begin, you must remove any containers you previously ran for this guide. To stop and remove a container, either:

• In a terminal, run docker remove --force my-mysql to remove the container named my-mysql.
• Or, in the Docker Desktop Dashboard, select the Delete icon next to your container in the Containers view.

そこで Docker Desktop GUI または CUI を使って、ボリュームを使ったコンテナーを起動します。

At this point, any MySQL container that mounts the my-db-volume will be able to access and save persisted data.

Build a customized database image

Customizing your database image lets you include additional configuration, scripts, or tools alongside the base database server. This is particularly useful for creating a Docker image that matches your specific development or production environment needs. The following example outlines how to build and run a custom MySQL image that includes a table initialization script.

Before you begin, you must remove any containers you previously ran for this guide. To stop and remove a container, either:

• In a terminal, run docker remove --force my-mysql to remove the container named my-mysql.
• Or, in the Docker Desktop Dashboard, select the Delete icon next to your container in the Containers view.

To build and run your custom image:

1. Create a Dockerfile.

   1. Create a file named Dockerfile in your project directory. For this example, you can create the Dockerfile in an empty directory of your choice. This file will define how to build your custom MySQL image.

   2. Add the following content to the Dockerfile.

      # syntax=docker/dockerfile:1
      
      # Use the base image mysql:latest
      FROM mysql:latest
      
      # Set environment variables
      ENV MYSQL_DATABASE mydb
      
      # Copy custom scripts or configuration files from your host to the container
      COPY ./scripts/ /docker-entrypoint-initdb.d/

      In this Dockerfile, you've set the environment variable for the MySQL database name. You can also use the COPY instruction to add custom configuration files or scripts into the container. In this example, files from your host's ./scripts/ directory are copied into the container's /docker-entrypoint-initdb.d/ directory. In this directory, .sh, .sql, and .sql.gz scripts are executed when the container is started for the first time. For more details about Dockerfiles, see the Dockerfile reference.

   3. Create a script file to initialize a table in the database. In the directory where your Dockerfile is located, create a subdirectory named scripts, and then create a file named create_table.sql with the following content.

   CREATE TABLE IF NOT EXISTS mydb.myothertable (
     column_name VARCHAR(255)
   );
   
   INSERT INTO mydb.myothertable (column_name) VALUES ('other_value');

   You should now have the following directory structure.

   ├── your-project-directory/
   │ ├── scripts/
   │ │ └── create_table.sql
   │ └── Dockerfile

2. Build your image.

   1. In a terminal, change directory to the directory where your Dockerfile is located.

   2. Run the following command to build the image.

      $ docker build -t my-custom-mysql .
      

      In this command, -t my-custom-mysql tags (names) your new image as my-custom-mysql. The period (.) at the end of the command specifies the current directory as the context for the build, where Docker looks for the Dockerfile and any other files needed for the build.

3. Run your image as you did in Run a local containerized database. This time, specify your image's name instead of mysql:latest. Also, you no longer need to specify the MYSQL_DATABASE environment variable as it's now defined by your Dockerfile.

   $ docker run --name my-mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -d my-custom-mysql
   

4. Verify that your container is running with the following command.

   $ docker ps
   

   You should see output like the following.

   CONTAINER ID   IMAGE              COMMAND                  CREATED        STATUS          PORTS                 NAMES
   f74dcfdb0e59   my-custom-mysql   "docker-entrypoint.s…"    2 hours ago    Up 51 minutes   3306/tcp, 33060/tcp   my-mysql
   

5. Verify that your initialization script was ran. Run the following command in a terminal to show the contents of the myothertable table.

   $ docker exec my-mysql mysql -u root -pmy-secret-pw -e "SELECT * FROM mydb.myothertable;"
   

   You should see output like the following.

   column_name
   other_value
   

Any container ran using your my-custom-mysql image will have the table initialized when first started.

Use Docker Compose to run a database

Docker Compose is a tool for defining and running multi-container Docker applications. With a single command, you can configure all your application's services (like databases, web apps, etc.) and manage them. In this example, you'll create a Compose file and use it to run a MySQL database container and a phpMyAdmin container.

To run your containers with Docker Compose:

1. Create a Docker Compose file.

   1. Create a file named compose.yaml in your project directory. This file will define the services, networks, and volumes.

   2. Add the following content to the compose.yaml file.

      services:
        db:
          image: mysql:latest
          environment:
            MYSQL_ROOT_PASSWORD: my-secret-pw
            MYSQL_DATABASE: mydb
          ports:
            - 3307:3306
          volumes:
            - my-db-volume:/var/lib/mysql
      
        phpmyadmin:
          image: phpmyadmin/phpmyadmin:latest
          environment:
            PMA_HOST: db
            PMA_PORT: 3306
            MYSQL_ROOT_PASSWORD: my-secret-pw
          ports:
            - 8080:80
          depends_on:
            - db
      
      volumes:
        my-db-volume:

      For the database service:

      • db is the name of the service.
      • image: mysql:latest specifies that the service uses the latest MySQL image from Docker Hub.
      • environment lists the environment variables used by MySQL to initialize the database, such as the root password and the database name.
      • ports maps port 3307 on the host to port 3306 in the container, allowing you to connect to the database from your host machine.
      • volumes mounts my-db-volume to /var/lib/mysql inside the container to persist database data.

      In addition to the database service, there is a phpMyAdmin service. By default Compose sets up a single network for your app. Each container for a service joins the default network and is both reachable by other containers on that network, and discoverable by the service's name. Therefore, in the PMA_HOST environment variable, you can specify the service name, db, in order to connect to the database service. For more details about Compose, see the Compose file reference.

2. Run Docker Compose.

   1. Open a terminal and change directory to the directory where your compose.yaml file is located.

   2. Run Docker Compose using the following command.

      $ docker compose up
      

      You can now access phpMyAdmin at http://localhost:8080 and connect to your database using root as the username and my-secret-pw as the password.

   3. To stop the containers, press ctrl+c in the terminal.

Now, with Docker Compose you can start your database and app, mount volumes, configure networking, and more, all with a single command.

Summary

This guide introduced you to the essentials of using containerized databases, specifically focusing on MySQL, to enhance flexibility, ease of setup, and consistency across your development environments. The use-cases covered in this guide not only streamline your development workflows but also prepare you for more advanced database management and deployment scenarios, ensuring your data-driven applications remain robust and scalable.

Related information:

• Docker Hub database images
• Dockerfile reference
• Compose file reference
• Database samples