Spring Boot container cannot connect to My SQL container

Question

I have read all questions related the issue and controlled all points. It seems everything is ok with my codes but it doesn't connect anyway. I got CONNECTION REFUSED error when I try to connect from container. (BTW. Everything is fine when I change URL and try to connect from localhost)

My java project

spring:
  datasource:
   url: jdbc:mysql://mysqldb:3306/bootdb
   username: root
   password: root
  jpa:
    properties:
      hibernate:
        dialect: org.hibernate.dialect.MySQL5InnoDBDialect
    hibernate:
      ddl-auto: update
    database-platform: org.hibernate.dialect.MySQL5Dialect
    generate-ddl: true

My docker-compose file

version: "3"
services:
  mysqldb:
    image: mysql
    ports:
      - "3306:3306"
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: bootdb
    networks:
      - testnetwork
  employee-jdbc:
    image: bago1/student:latest
    restart: always
    build: .
    ports:
      - 8080:8080
    networks:
      - testnetwork
    depends_on:
      - mysqldb
    links:
      - mysqldb
networks:
  testnetwork:

It successfully connects from my local host machine when I edit URL as

url: jdbc:mysql://mysqldb:3306/bootdb

1. DB works fine
2. They are on the same network
3. syntax is fine

Answer 1

Add the hostname field in your docker compose like this:

version: "3"
services:
  mysqldb:
    image: mysql
    hostname: mysqldb
    ports:
      - "3306:3306"
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: bootdb
  employee-jdbc:
    image: bago1/student:latest
    restart: always
    build: .
    ports:
      - 8080:8080
    depends_on:
      - mysqldb
    links:
      - mysqldb

(Ps: don't need the add the networks field, the use of docker-compose creates automatically a network for your services)

(PS2: it's a good practice to use tag when using images (instead of using mysql:latest) )