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I need to use two containers together: one with Tomcat and another with a Database.
I have created the following yaml file which describes the services:
postgredb:
image: postgres
expose:
- 5432
ports:
- 5432:5432
environment:
- POSTGRES_USER=user
- POSTGRES_PASSWORD=password
tomcat:
image: tomcat
links:
- postgredb:db
ports:
- 8080:8080
After starting docker-compose I can see that I'm not able to reach the Database from Tomcat, unless I retrieve the IP address of the Database (via docker inspect) and use it when configuring Tomcat Connection Pool to the DB.
From my understanding, the two containers should be linked and I'd expect to find the database on localhost at port 5432, otherwise I see little benefits in linking the containers.
Is my understanding correct?
694
If you set a predictable project name for the first composition you can use external_links to reference external containers by name from a different compose file. In the next docker-compose release (1.6) you will be able to use user defined networks, and have both compositions join the same network.
A Docker network lets your containers communicate with each other. If you are running more than one container, you can let your containers communicate with each other by attaching them to the same network. Docker creates virtual networks which let your containers talk to each other.
Use the alias "db" that you have defined in file to refer to the database host name.
Containers for the linked service will be reachable at a hostname identical to the alias, or the service name if no alias was specified.
Source: https://docs.docker.com/compose/compose-file/compose-file-v2/#links
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