Docker-compose MySQL link failure - mysql

Question

EDIT: I've managed to get it to work
I'm currently using docker in combination with a Dockerfile and a docker-compose.yml i'm trying to run my backend so i can use Postman to get data from the database. However I keep getting Communication Link Failure
com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
Dockerfile
FROM openjdk:8-jdk-alpine
EXPOSE 8080
ADD /build/libs/assignment_4-0.0.1-SNAPSHOT.jar spring-docker.jar
ENTRYPOINT ["java", "-jar", "spring-docker.jar"]
docker-compose.yml
version: '3'
services:
docker-mysql:
restart: always
container_name: docker-mysql
image: mysql:5.7
environment:
MYSQL_DATABASE: database
MYSQL_ROOT_PASSWORD: root
MYSQL_ROOT_HOST: '%'
volumes:
- ./sql:/docker-entrypoint-initdb.d
ports:
- "3306:3306"
app:
image: springio/docker
expose:
- "8080"
ports:
- 8080:8080
environment:
WAIT_HOSTS: mysql:3306
depends_on:
- docker-mysql
application.properties
spring.jpa.hibernate.ddl-auto=none
spring.datasource.url=jdbc:mysql://docker-mysql:3306/database
spring.datasource.username=root
spring.datasource.password=root
# To keep the database connection alive while idle for a long time
spring.datasource.testWhileIdle = true
spring.datasource.validationQuery = SELECT 1
The API is made with SpringBoot using Kotlin. Can someone help me figure out how to resolve this problem?

Answer 1

To achieve the correct order of services to start you need to add 2 things:
Set container's names to let them ping each other by these names (by means of docker bridge)
Enforce your app to wait for DB fully up before connect.
From point of this your Dockerfile could look like this (let we choose wait-for-it)
FROM openjdk:8-jdk-alpine
EXPOSE 8080
RUN apk add --no-cache bash
RUN wget -q https://github.com/vishnubob/wait-for-it/raw/master/wait-for-it.sh -O /usr/bin/wait-for-it && \
chmod +x /usr/bin/wait-for-it
ADD /build/libs/assignment_4-0.0.1-SNAPSHOT.jar spring-docker.jar
ENTRYPOINT /usr/bin/wait-for-it docker-mysql-container:3306 -t 120 ; java -jar spring-docker.jar
While docker-compose.yml should include
version: '3'
networks:
database:
services:
docker-mysql:
networks:
- database
container_name: docker-mysql-container
...
app:
networks:
- database
container_name: app-container
...
And replace in your application.properties service's name docker-mysql with container's name docker-mysql-container