Docker Compose + Spring Boot + Postgres connection, resulting in error

Question

I have a Java Spring Boot app which works with a Postgres database. I want to use Docker for both of them. Initially, I created a docker-compose.yml file as given below:

version: '3'
services:
  db:
    container_name: sample_db
    image: postgres
    volumes:
      - sample_db:/var/lib/postgresql/data
    ports:
      - "5432:5432"
    environment:
      - POSTGRES_DB="employee"
      - POSTGRES_USER="user"
      - POSTGRES_PASSWORD="password"
      - PGDATA=/var/lib/postgresql/data/pgdata

  web:
    build: .
    expose:
      - "8080"
    depends_on:
      - db
volumes:
  sample_db: {}

Then, in my Spring Boot app, inside the application.properties file I defined the following properties.

spring.datasource.url=jdbc:postgresql://db:5432/employee
spring.datasource.username=user
spring.datasource.password=password

along with this,I created a Dockerfile in my project directory, which looks like this:

FROM openjdk:8-jdk-alpine
EXPOSE 8080    
ARG JAR_FILE=target/employee-0.0.1-SNAPSHOT.jar    
COPY ${JAR_FILE} employee-demo.jar    
ENTRYPOINT ["java","-jar","employee-demo.jar"]

I issued these commands and ended up in the error as given below

mvn clean package

docker-compose up

The problem is the connection string. I believe I have to change it to something else, but I don't know what it should be. I get the following error messages:

 Caused by: org.postgresql.util.PSQLException: The connection attempt failed.
web_1  |    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:292) ~[postgresql-42.2.5.jar!/:42.2.5]
web_1  |    at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:49) ~[postgresql-42.2.5.jar!/:42.2.5]
web_1  |    at org.postgresql.jdbc.PgConnection.<init>(PgConnection.java:195) ~[postgresql-42.2.5.jar!/:42.2.5]
web_1  |    at org.postgresql.Driver.makeConnection(Driver.java:454) ~[postgresql-42.2.5.jar!/:42.2.5]
web_1  |    at org.postgresql.Driver.connect(Driver.java:256) ~[postgresql-42.2.5.jar!/:42.2.5]
web_1  |    at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:136) ~[HikariCP-3.2.0.jar!/:na]
web_1  |    at com.zaxxer.hikari.pool.PoolBase.newConnection(PoolBase.java:369) ~[HikariCP-3.2.0.jar!/:na]
web_1  |    at com.zaxxer.hikari.pool.PoolBase.newPoolEntry(PoolBase.java:198) ~[HikariCP-3.2.0.jar!/:na]
web_1  |    at com.zaxxer.hikari.pool.HikariPool.createPoolEntry(HikariPool.java:467) ~[HikariCP-3.2.0.jar!/:na]
web_1  |    at com.zaxxer.hikari.pool.HikariPool.checkFailFast(HikariPool.java:541) ~[HikariCP-3.2.0.jar!/:na]
web_1  |    at com.zaxxer.hikari.pool.HikariPool.<init>(HikariPool.java:115) ~[HikariCP-3.2.0.jar!/:na]
web_1  |    at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:112) ~[HikariCP-3.2.0.jar!/:na]
web_1  |    at org.hibernate.engine.jdbc.connections.internal.DatasourceConnectionProviderImpl.getConnection(DatasourceConnectionProviderImpl.java:122) ~[hibernate-core-5.3.7.Final.jar!/:5.3.7.Final]
web_1  |    at org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess.obtainConnection(JdbcEnvironmentInitiator.java:180) ~[hibernate-core-5.3.7.Final.jar!/:5.3.7.Final]
web_1  |    at org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl.getIsolatedConnection(DdlTransactionIsolatorNonJtaImpl.java:43) ~[hibernate-core-5.3.7.Final.jar!/:5.3.7.Final]
web_1  |    ... 44 common frames omitted
web_1  | Caused by: java.net.UnknownHostException: sample_db
web_1  |    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184) ~[na:1.8.0_181]
web_1  |    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:1.8.0_181]
web_1  |    at java.net.Socket.connect(Socket.java:589) ~[na:1.8.0_181]
web_1  |    at org.postgresql.core.PGStream.<init>(PGStream.java:70) ~[postgresql-42.2.5.jar!/:42.2.5]
web_1  |    at org.postgresql.core.v3.ConnectionFactoryImpl.tryConnect(ConnectionFactoryImpl.java:91) ~[postgresql-42.2.5.jar!/:42.2.5]
web_1  |    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:192) ~[postgresql-42.2.5.jar!/:42.2.5]
web_1  |    ... 58 common frames omitted

Am new to docker, If any issues please inform

Answer 1

It was because of the " " given mistakenly. I changed it to

version: '3'
services:
  db:
    restart: always
    image: postgres
    ports:
      - "5432:5432"
    environment:
      - POSTGRES_DB=employee
      - POSTGRES_USER=user
      - POSTGRES_PASSWORD=password

  web:
    build: .
    ports:
      - 8080:8080

Now it is working fine. Thank you for your valuable time.

Answer 2

Your service name is db, which is what you'll need to reference as the hostname from your web container. The container name, sample_db, is not resolvable from the web container because you have not specified a network, and thus are using the default bridge network.

According to the docs, the default bridge network doesn't provide name resolution between containers, only IP. Using docker compose, you should be able to resolve using the service name.

https://docs.docker.com/network/bridge/

https://docs.docker.com/compose/networking/

version: '3'
services:
  db:
    container_name: sample_db
    image: postgres
    volumes:
      - sample_db:/var/lib/postgresql/data
    ports:
      - "5432:5432"
    environment:
      - POSTGRES_DB="employee"
      - POSTGRES_USER="user"
      - POSTGRES_PASSWORD="password"
      - PGDATA=/var/lib/postgresql/data/pgdata
    networks:
      - my_network
  web:
    build: .
    expose:
      - "8080"
    depends_on:
      - db
    networks:
      - my_network
volumes:
  sample_db: {}
networks:
  my_network:
    driver: bridge

A link should also work instead of defining your own custom bridge network:

  web:
    build: .
    expose:
      - "8080"
    depends_on:
      - db
    links:
      - "db:sample_db"