Deploy Spring Boot and MySQL using Docker compose

When working with Dockerized databases, it’s crucial to use the container name for the host instead of the service name in your code.

Therefore, your connection string should be:

jdbc:mysql://mysql-container:3306/inventory?autoReconnect=true&useSSL=false

as you specified your MySQL container name on your docker-compose.yaml.

To ensure compatibility both locally and in Docker, adjust your application.properties file as follows:

spring.datasource.url=${MYSQL_URL:jdbc:mysql://localhost:3306/inventory?autoReconnect=true&useSSL=false}

and set on your docker-compose.yaml on the spring-app service the environment variable:

environment:
    MYSQL_URL: jdbc:mysql://mysql-container:3306/inventory?autoReconnect=true&useSSL=false

or

you can specify just the host part, like this:

spring.datasource.url=jdbc:mysql://${MYSQL_HOST:localhost}:3306/inventory?autoReconnect=true&useSSL=false

and set on your docker-compose.yaml on the spring-app service the env:

environment:
    MYSQL_HOST: mysql-container

This way when you run locally without the env it will use your localhost database and when you Dockerize your application you will pass an env with the correct host for your connection string.

You can see an example on running an application with Dockerized PostgreSQL on this Baeldung article: https://www.baeldung.com/spring-boot-postgresql-docker

UPDATE:

Another thing that you should do to work is add an restart-policy to your spring-app. The depends_on keyword on his own is not enough.

This is what happens when you execute the docker compose up. The docker will initialize your mysql-db, and after it initializes the depends_on policy will make your spring-app initializes in sequence, but there is the problem, your database is initialized, but not fully loaded and working. So when you load your spring-app it will not find a database and will fail.

To prevent this, you should add an restart policy to your spring-app, so when it loads and not found a database it will fail but will start another on sequence. Add it like this:

      spring-app:
        build:
          context: .
          dockerfile: Dockerfile
        container_name: spring-container
        ports:
          - "8082:8080"
        depends_on:
          - mysql-db
        environment:
          MYSQL_URL: jdbc:mysql://mysql-container:3306/inventory?autoReconnect=true&useSSL=false
          MYSQL_USERNAME: root
          MYSQL_PASSWORD: root
        deploy:
          restart_policy:
            condition: on-failure
            max_attempts: 10

with this it will try to restart your application until it runs properly, at max 10 times.

The name of the environment variable doesn’t matter, as long as is the same as you specify on your application.properties. As a convention I recommend you to use the MYSQL_URL name for the env, because SPRING_DATASOURCE_URL gives an impression that is an Spring provided property. You should end with something like this:

    spring.datasource.url=${MYSQL_URL:jdbc:mysql://localhost:3306/inventory?autoReconnect=true&useSSL=false}
    spring.datasource.username=${MYSQL_USERNAME:root}
    spring.datasource.password=${MYSQL_PASSWORD:root}

Attention: The spring.datasource.url is not an environment variable, just what is inside the ${ } is one.

I would also recommend you to connect your app and database to the same docker network. Providing better isolation, security and communication, preventing from eventual communication issues.

Following everything you should end with an docker-compose like this:

version: '3.8'
services:
  mysql-db:
    image: mysql:8.0
    container_name: mysql-container
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: inventory
      MYSQL_USER: user
      MYSQL_PASSWORD: password
    ports:
      - "3306:3306"
    networks:
      - springmysql

  spring-app:
    build:
      context: .
      dockerfile: Dockerfile
    container_name: spring-container
    ports:
      - "8082:8080"
    depends_on:
      - mysql-db
    environment:
      MYSQL_URL: jdbc:mysql://mysql-container:3306/inventory?autoReconnect=true&useSSL=false
      MYSQL_USERNAME: root
      MYSQL_PASSWORD: root
    deploy:
      restart_policy:
        condition: on-failure
        max_attempts: 10
    networks:
      - springmysql

networks:
  springmysql:
    name: springmysql