Proper setup of docker compose with spring boot and postgres

I have a docker compose file where i have two services the flamup service is used for building my spring boot application and links to a postgres image defined by the db service.

Here's the docker-compose.yml file

version: '3.8'


volumes:
  postgres_data:

services:

  flamup:
    build: .
    container_name: flamup
    environment:
      - DB_SERVER=db
      - POSTGRES_DB=flamup
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=postgres
    ports:
      - "8080:8080" # Forward the exposed port 8080 on the container to port 8080 on the host machine
    depends_on:
      - db
    links:
      - db



  db:
    image: "postgres:9.6-alpine"
    container_name: postgres_container
    restart: always

    volumes:
      - postgres_data:/var/lib/postgresql/data

    ports:
      - "5432:5432"

    environment:
      - POSTGRES_DB=flamup
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=postgres
      - PGDATA=/var/lib/postgresql/data/pgdata

Here's the Dockerfile for the spring boot application

FROM maven:3.6.1-jdk-8-slim AS build
RUN mkdir -p workspace
WORKDIR workspace
COPY pom.xml /workspace
COPY src /workspace/src
COPY frontend /workspace/frontend
COPY data2.csv /workspace
RUN mvn -f pom.xml clean package
#RUN ./mvnw clean package -DskipTests

#FROM adoptopenjdk/openjdk11:alpine-jre
FROM openjdk:8-alpine
COPY --from=build /workspace/target/*.jar app.jar
EXPOSE 8080
ENTRYPOINT ["java","-jar","app.jar"]

I am using the frontend-maven-plugin for bootstrapping the frontend with the spring boot application. Everything works fine locally.

However when i try to run it via docker-compose i made some changes in the application-properties.yml

server:
  error:
    include-message: always
    include-binding-errors: always


spring:
  datasource:
    url : jdbc:postgresql://${DB_SERVER}/${POSTGRES_DB}
    username : ${POSTGRES_USER}
    password : ${POSTGRES_PASSWORD}

  jpa:
    hibernate:
      ddl-auto: create
    properties:
      hibernate:
        dialect: org.hibernate.dialect.PostgreSQLDialect
        format_sql: true
        jdbc:
          lob:
            non_contextual_creation: true
    show-sql: true

  session:
    store-type: jdbc
    jdbc:
      table-name: SPRING_SESSION
      initialize-schema: never

However the build get's failed everytime, because of this

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaConfiguration.class]: Invocation of init method failed; nested exception is javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory; nested exception is org.hibernate.exception.JDBCConnectionException: Unable to open JDBC Connection for DDL execution
Caused by: javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory; nested exception is org.hibernate.exception.JDBCConnectionException: Unable to open JDBC Connection for DDL execution
Caused by: org.hibernate.exception.JDBCConnectionException: Unable to open JDBC Connection for DDL execution
Caused by: org.postgresql.util.PSQLException: The connection attempt failed.
Caused by: java.net.UnknownHostException: ${DB_SERVER}

Things i have tried

• Hard coding the DB_SERVER variable and replacing with localhost:5432 , db , db:5432. None of the seems to work.
• Adding depends on field in the flamup service.
• Adding networks field in both the services and connecting them via a bridge.
• Tried different versions of postgres and maven

Nothing seems to be the solution, any help will be highly appreciated.