How to link multiple docker-compose services via network

New scenario: Sharing a network between services

If you want define services in multiple docker-compose.yml files, and also have network connectivity between the services, you need to configure your services to use the same network.

To create an external network, you can run docker network create <name>. -- where <name> can be a single string without spaces.

Creating the network

$ docker network create external-example
2af4d92c2054e9deb86edaea8bb55ecb74f84a62aec7614c9f09fee386f248a6

Modified first docker-compose file with network configured

version: '3' 
services: 
  service1: 
    image: busybox 
    command: sleep infinity 

networks: 
  default: 
    external: 
      name: external-example 

Restarting the services

$ pwd
/tmp/docker-example/compose1

$ docker-compose up -d
Creating compose1_service1_1 ... done

Modified second docker-compose file with network configured

version: '3' 
services: 
  service2: 
    image: busybox 
    command: sleep infinity 

networks: 
  default: 
    external: 
      name: external-example 

Restarting the services

$ pwd
/tmp/docker-example/compose2

$ docker-compose up -d
Creating compose2_service2_1 ... done

After running docker-compose up -d on both docker-compose.yml files, we see that no new networks were created.

$ docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
25e0c599d5e5        bridge              bridge              local
2af4d92c2054        external-example    bridge              local
7df4631e9cff        host                host                local
194d4156d7ab        none                null                local

With the containers using the external-example network, they are able to ping one another.

Test: Service 1 ping Service 2

# By service name
$ docker exec -it compose1_service1_1 ping service2
PING service2 (172.24.0.3): 56 data bytes
64 bytes from 172.24.0.3: seq=0 ttl=64 time=0.054 ms
^C
--- service2 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max = 0.054/0.054/0.054 ms

# By container name
$ docker exec -it compose1_service1_1 ping compose2_service2_1
PING compose2_service2_1 (172.24.0.2): 56 data bytes
64 bytes from 172.24.0.2: seq=0 ttl=64 time=0.042 ms
^C
--- compose2_service2_1 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max = 0.042/0.042/0.042 ms

Test: Service 2 ping Service 1

# By service name
$ docker exec -it compose2_service2_1 ping service1
PING service1 (172.24.0.2): 56 data bytes
64 bytes from 172.24.0.2: seq=0 ttl=64 time=0.041 ms
^C
--- service1 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max = 0.041/0.041/0.041 ms

# By container name
$ docker exec -it compose2_service2_1 ping compose1_service1_1
PING compose1_service1_1 (172.24.0.3): 56 data bytes
64 bytes from 172.24.0.3: seq=0 ttl=64 time=0.042 ms
^C
--- compose1_service1_1 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max = 0.042/0.042/0.042 ms