Error creating a docker-compose connecting a java and a mysql containers-CodePudding

I am trying to connect the container of my springboot application with the container of a mysql image using docker-compose, however when I run docker-compose up my terminal starts a loop where it starts the spring application, try to connect with the MySQL container, fails and keep trying. The error that I get is com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failures

docker-compose file:

version: '3.8'

services:
  mysqldb:
    image: mysql
    platform: linux/x86_64
    env_file: ./.env
    restart: always
    environment:
      - MYSQL_ROOT_PASSWORD=$MYSQLDB_ROOT_PASSWORD
      - MYSQL_DATABASE=$MYSQLDB_DATABASE
    ports:
      - $MYSQLDB_LOCAL_PORT:$MYSQLDB_DOCKER_PORT
    volumes:
      - db:/var/lib/mysql
  app:
    depends_on:
     - mysqldb
    build: .
    restart: always
    env_file: ./.env
    ports:
      - $APP_LOCAL_PORT:$APP_DOCKER_PORT
    environment:
      - DB_HOST=mysqldb
      - DB_USER=$MYSQLDB_USER
      - DB_PASSWORD=$MYSQLDB_ROOT_PASSWORD
      - DB_NAME=$MYSQLDB_DATABASE
      - DB_PORT=$MYSQLDB_DOCKER_PORT
    stdin_open: true
    tty: true

volumes: 
  db:

.env:

MYSQLDB_USER=root
MYSQLDB_ROOT_PASSWORD=12345678
MYSQLDB_DATABASE=dronefeederdb
MYSQLDB_LOCAL_PORT=3306
MYSQLDB_DOCKER_PORT=3306

APP_LOCAL_PORT=8080
APP_DOCKER_PORT=8080

Application.yaml:

server:
  port: 8080
spring:
    datasource:
        username: ${DB_USER}
        password: ${DB_PASSWORD}
        url: jdbc:mysql://${DB_HOST}:${DB_PORT}/${DB_NAME}
    jpa:
        hibernate:
            ddl-auto: update
        show-sql: true
        open-in-view: false
        #https://ia-tec-development.medium.com/lombok-e-spring-data-jpa-142398897733
    security.user:
        name: dronefeeder
        password: dronefeeder
        #https://www.baeldung.com/spring-boot-security-autoconfiguration


resilience4j.circuitbreaker:
  configs:
    default:
      waitDurationInOpenState: 10s
      failureRateThreshold: 10
  #instances:
    #estudantes:
      #baseConfig: default

Dockerfile:

FROM openjdk:11.0-jdk as build-image
WORKDIR /app
COPY . .
RUN ./mvnw clean package -DskipTests

FROM openjdk:11.0-jre
COPY --from=build-image /app/target/*.jar /app/app.jar
EXPOSE 8080
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom", "-jar", "/app/app.jar"]

Repository link: https://github.com/julia-baptista/dronefeeder/tree/docker-configuration

CodePudding user response：

I believe the issue is your application's use of localhost for the SQL URL in the Application.yaml property file. Since your app runs on a container by itself it tries to look at localhost of the container, while your SQL server is in another container, with its own localhost. Localhost in docker container do not refer to the host, they refer to the localhost within the container itself. If you want to access the host machine, this is an excellent answer From inside of a Docker container, how do I connect to the localhost of the machine?

url: jdbc:mysql://localhost:3306/dronefeederdb

localhost should not be used, you need to use the sql continainer url.

The fastest option is to use host.docker.internal instead of localhost. But its not the best.

Another quick option is to run the two containers on the same docker network. Define that in your compose file the same way as the volumes. Then set each container to that network. See Networking in Compose. Then you can set your SQL url to use the SQL container name instead of localhost. So this.. url: jdbc:mysql://localhost:3306/dronefeederdb becomes url: jdbc:mysql://mysql/dronefeederdb

Neither option is robust, since you're hardcoding the container name in the application property file. A better solution is to have an environment variable in your webApp image that can accept the URL to the SQL server. Then you can provide the SQL location when running the container, or in your compose file (Environment variables in Compose). This way the SQL server can be anywhere.

CodePudding user response：

You need to add in the app definition block a depends on: sentence, to make docker compose to not boot the application until the database is up.

Check this documentation: Docker Compose Startup Order