springboot application cannot establish connection with sql database running on docker

Question

I have a project running in localhost using intellij as the Springboot instance, using Xampp's SQL without any issues. This works very well. But now I want to deploy everything to docker. So I created a dockerfile and a docker-compose up file in my directory like this:

-Application
 |
  -Frontend (not in docker implemented yet)
  -Backend(springAPI)
   |
    -dockerfile
  -Python (flaskAPI) (not in docker implemented yet)
docker-compose.yml

docker-compose.yml looks like this:

version: '3.9'

services:
  db:
    image: mysql:latest
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: <pass>
      MYSQL_DATABASE:mydb
      MYSQL_USER: <user>
      MYSQL_PASSWORD: <pass>
    ports:
      - "3306:3306"
    volumes:
      - ./data:/var/lib/mysql

  phpmyadmin:
    image: phpmyadmin/phpmyadmin:latest
    restart: always
    depends_on:
      -db
    ports:
      - "8888:80"
    environment:
      PMA_HOST: db
      MYSQL_ROOT_PASSWORD: example

  spring-api:
    image: spring-api:latest
    ports:
      - "8080:8080"
    depends_on:
      -db

volumes:
  dbdata:
  mysql-data:

The dockerfile of springapi is as follows:

# Use an official OpenJDK runtime as a parent image
FROM openjdk:17-jdk-slim

# Set the working directory to /app
WORKDIR/app

# Copy the application jar file to the container
COPY build/libs/backendAPI.jar backendAPI.jar

# Run the application
CMD ["java", "-jar", "backendAPI.jar"]

This can be composed of docker and run containers. How does java spring boot throw an error and shut down.The error is:

`2023-03-06T12:25:37.603Z INFO 1 --- [main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Starting. ..

2023-03-06T12:25:38.685Z ERROR 1 --- [main] com.zaxxer.hikari.pool.HikariPool : HikariPool-1 - Exception during pool initialization.


com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure


The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.`

I tried reconfiguring my application.settings like this:

spring.datasource.url=jdbc:mysql://localhost:8888/mydb
spring.datasource.username=<theusername>
spring.datasource.password=<thepassword>
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

But it has no effect. Because it keeps throwing the same error. The SQL server can be accessed via the given url. So running fine (except not having admin rights, but that's a different issue.)

This setup, with some tweaks to application.settings, works great when I'm just using Xammp and intellij. But now I can't connect it. What am I missing here?

Edit what I've tried so far

db:
    image: mysql:latest
    restart: always
    container_name: sql-db

Then change application.settings:

spring.datasource.url=jdbc:mysql://sql-db:8888/mydb (and also with sql-db:3306)

;

But this still gives the same error.

Answer 1

Specify a container name for your database service in the docker compose file

db:
    image: mysql:latest
    restart: always
    **container_name: db-container**

Then in your jdbc url you should reference the configured database container name and the actual configured port of the database container.

So your datasource.url looks like

spring.datasource.url=jdbc:mysql://db-container:3306/mydb