Connect service container to db container - spring-boot

Question

I'm new to docker and started to play with it on my small project.
I have dockerized the service itself with the following Docker file:
ROM adoptopenjdk:11-jdk-hotspot AS DEPENDENCIES_BUILD_IMAGE
ENV APP_HOME=/usr/app/
WORKDIR $APP_HOME
COPY build.gradle settings.gradle gradlew $APP_HOME
COPY gradle $APP_HOME/gradle
RUN ./gradlew build || return 0
COPY . .
RUN ./gradlew build
FROM adoptopenjdk/openjdk11:jdk-11.0.7_10-alpine AS FINAL
ENV JAR_TEMPLATE=myapp-0.0.1-SNAPSHOT.jar
ENV ARTIFACT_NAME=myapp.jar
ENV APP_HOME=/usr/app
WORKDIR $APP_HOME
COPY --from=DEPENDENCIES_BUILD_IMAGE $APP_HOME/build/libs/$JAR_TEMPLATE .
RUN mv $JAR_TEMPLATE $ARTIFACT_NAME
EXPOSE 8080
CMD ["java", "-jar", "budget-calculator.jar"]
Side note - I know that there's a problem that I'm always copying 0.0.1-SNAPSHOT - but I'm not sure how to solve it at the moment.
After that I wanted to connect my service to a Postgres DB with docker-compose using this confirmation:
version: '3'
services:
backend:
build: .
container_name: myapp
ports:
- "8080:8080"
links:
- "db"
depends_on:
- db
networks:
- backend
db:
restart: unless-stopped
image: postgres:10
container_name: myapp-db
environment:
- POSTGRES_USER=postgres
- POSTGRES_PASSWORD=secret
- POSTGRES_DB=myapp
ports:
- 5436:5436
networks:
- backend
networks:
backend:
After that I've updated my application.properties file to indicate that the DB link is on the other container as follow:
spring.flyway.url=jdbc:postgresql://db:5436/myapp
spring.flyway.user=postgres
spring.flyway.password=secret
spring.flyway.baseline-on-migrate=true
spring.datasource.url=jdbc:postgresql://db:5436/myapp
spring.datasource.username=postgres
spring.datasource.password=secret
spring.datasource.driverClassName=org.postgresql.Driver
Now I had 2 problems:
While I assumed that build: . will rebuild my image every time
that I'm running docker-compose up if something changed in
practice I saw that it's not the case.
When the backend service starts flyway (a migration DB library) try
to connect to the database and cannot resolve the connection.
I've seen online that the usage of - links is deprecated and I should use the networks but both do not seem to work - what am I missing?

Answer 1

There are 2 problems with my configurations, the first one - the internal port of Postgres was configured as 5436 while the default port of the image is 5432 (I've updated both of them to 5432)
the second one, in order to pass the IP of the DB to the service I've added the following environment variables to the service image:
environment: # Pass environment variables to the service
SPRING_DATASOURCE_URL: jdbc:postgresql://db:5432/budget
SPRING_DATASOURCE_USERNAME: postgres
SPRING_DATASOURCE_PASSWORD: secret
SPRING_FLYWAY_URL: jdbc:postgresql://db:5432/budget
SPRING_FLYWAY_USER: postgres
SPRING_FLYWAY_PASSWORD: secret
So my current working configuration is this:
version: '3.8'
services:
backend:
build: .
container_name: app-service
ports:
- "8080:8080"
depends_on:
- db
environment: # Pass environment variables to the service
SPRING_DATASOURCE_URL: jdbc:postgresql://db:5432/myapp
SPRING_DATASOURCE_USERNAME: postgres
SPRING_DATASOURCE_PASSWORD: secret
SPRING_FLYWAY_URL: jdbc:postgresql://db:5432/myapp
SPRING_FLYWAY_USER: postgres
SPRING_FLYWAY_PASSWORD: secret
db:
restart: unless-stopped
image: postgres:10
environment:
- POSTGRES_DB=myapp
- POSTGRES_PASSWORD=postgres
- POSTGRES_USER=secret
volumes:
- myapp_data:/var/lib/postgresql/data
ports:
- 5432:5432
volumes:
myapp_data: