Cannot link to a running container started by docker-compose

Question

I am setting up my local development environment with docker containers. The docker-compose.yml is like following

version: \'2\'

services:
  db:
    image:         


        

Answer 1

When you use service definition version 2 and more, docker-compose creates user-defined network. Name resolution in a user-defined network works via Docker embedded DNS server. Here's related quote from documentation:

The Docker embedded DNS server enables name resolution for containers connected to a given [user-defined] network. This means that any connected container can ping another container on the same network by its container name.

Containers are also available by network aliases that docker-compose creates. It can be verified by command like:

docker inspect \
  -f '{{json .NetworkSettings.Networks.myapp_default.Aliases}}' my_app_db_1

It prints ["db","$CONTAINER_ID"].

Providing links with --link will not have any effect in case of existing user-defined network. You can make sure and look at /etc/hosts, which will not have the corresponding lines.

Thus the following command is sufficient:

docker run -it --net myapp_default worker