Docker Compose connect to external Postgres databases

Question

I have a SpringBoot application that works perfectly. Now I am trying to Dockerise it, but have some issues when connecting to the database.

The application has two datasources:

application.properties

server.port= 8081
# pims datasource
spring.datasource1.driver-class-name=org.postgresql.Driver
spring.datasource1.jdbc-url=jdbc:postgresql://localhost:5432/pims
spring.datasource1.username=postgres
spring.datasource1.password=
spring.jpa.database-platform=postgres
#spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQLDialect
spring.jpa.show-sql=false
# approval datasource
spring.datasource2.driver-class-name=org.postgresql.Driver
spring.datasource2.jdbc-url=jdbc:postgresql://localhost:5432/approval
spring.datasource2.username=postgres
spring.datasource2.password=

In the application, I use Spring to access the two datasources:

@Configuration
@ComponentScan(basePackages = "com.nexct")
public class MultipleDBConfig {

    @Bean(name = "datasource1")
    @ConfigurationProperties("spring.datasource1")
    @Primary
    public DataSource dataSource1(){
        return DataSourceBuilder.create().build();
    }

    @Bean(name = "datasource2")
    @ConfigurationProperties("spring.datasource2")
    public DataSource dataSource2(){
        return DataSourceBuilder.create().build();
    }
}

So I have created:

Dockerfile

FROM openjdk:14
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} nexct-approval-service.jar
EXPOSE 8081
ENTRYPOINT ["java","-jar","/nexct-approval-service.jar"]

docker-compose.yml

version: '3.7'

services:
  product-service:
    build: ../nexct-approval-service
    volumes:
      - ../nexct-approval-service:/usr/src/app
    ports:
      - "8081:8081"
    db:
      image: postgres
      environment:
        POSTGRES_DB_PORT: "5432"
        POSTGRES_DB_HOST: "localhost"
        POSTGRES_PASSWORD:
        POSTGRES_USER: postgres
        POSTGRES_DB: pims

However, I am not sure how to configure the two Postgres databases.

Any advise would be appreciated.

Note: the databases are not running in a container, as they are used by other legacy applications.

If I remove the db from docker-compose.yml. When I run docker-compose up, the Spring Boot application starts, and I can access a RESTful service. However, I get the following error:

PSQLException: Connection to localhost:5432 refused. Check that the hostname and port are correct and that the postmaster is accepting TCP/IP connections.

Answer 1

Try configuring your docker-compose file to use bridged networking:

version: '3.7'

services:
  product-service:
    build: ../nexct-approval-service
    volumes:
      - ../nexct-approval-service:/usr/src/app
    environment:
        POSTGRES_DB_PORT: "5432"
        POSTGRES_DB_HOST: "localhost"
        POSTGRES_PASSWORD:
        POSTGRES_USER: postgres
        POSTGRES_DB: pims
    networks:
        - product_service_network

networks:
    product_service_network:
        driver: bridge

You also have to move the ENVIRONMENT variables to product-service if you are going to use them in the product-service container.

If localhost doesn't work, use 127.0.0.1 instead.

Answer 2

version: '3.7'

services:
  product-service:
    build: ../nexct-approval-service
    volumes:
      - ../nexct-approval-service:/usr/src/app
    ports:
      - "8081:8081"

server.port=8081
# pims datasource
spring.datasource1.driver-class-name=org.postgresql.Driver
spring.datasource1.jdbc-url=jdbc:postgresql://<postgres_host_private_ip>:5432/pims
spring.datasource1.username=postgres
spring.datasource1.password=
spring.jpa.database-platform=postgres
#spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQLDialect
spring.jpa.show-sql=false
# approval datasource
spring.datasource2.driver-class-name=org.postgresql.Driver
spring.datasource2.jdbc-url=jdbc:postgresql://<postgres_host_private_ip>:5432/approval
spring.datasource2.username=postgres
spring.datasource2.password=

Replace <postgres_host_private_ip> with the private IP of the machine hosting the postgres databases.

I'm not sure what you were trying to achieve with the nested db service, but since your database are already running somewhere outside there is no need for this.

Your Spring application will run on a isolated network from your host because of the docker isolation (unless explicitly asked to use host network with network_mode: "host"). Knowing that, the "localhost" can not work inside the container, you need to use the real IP of the machine that hosts the databases. Most likely something like 192.168.xxx.xxx

Also, you need to make sure the postgres is configured to accept connection from "non-localhost" sources (see https://www.andrew-kirkpatrick.com/2017/05/allow-connection-postgresql-server-outside-localhost/).

Answer 3

To access an application running on ur Host there are few options

• Use the Bridge network. (Doc)
  • Create a bridge network and assign the subnet address and gateway address.
  • Now you can reach your application running at the host from the container at <gateway address>:<port> i.e 172.28.0.1:<port>

version: '3.7'

services:
  product-service:
    build: ../nexct-approval-service
    volumes:
      - ../nexct-approval-service:/usr/src/app
    ports:
      - "8081:8081"
    networks:
      hostnet: {}
           
networks:
  hostnet:
    driver: bridge
    ipam:
      config:
        - subnet: 172.28.0.0/16

• Use Attach service to host network. (Doc)
  • add network_mode: host to your service (only works on Linux)
  • OR create an external network
  • Now you can reach your application running at the host from the container at localhost:<port>

With network_mode: (Linux)

version: '3.7'

services:
 product-service:
   build: ../nexct-approval-service
   volumes:
     - ../nexct-approval-service:/usr/src/app
   ports:
     - "8081:8081"
   network_mode: host