# How to link multiple docker-compose services via network This scenario came from a question I was asked docker-compose and network connectivity between services defined in different docker-compose.yml files. The desired result was to be able to define a docker-compose.yml in one file, and in a second docker-compose.yml have the ability to reach the first service via service or container name for development purposes. ## Default scenario: Two separate docker-compose.yml and two separate default networks Let’s take a simple docker compose file. ```yaml version: '3' services: service1: image: busybox command: sleep infinity ``` When it starts up, a default network is created. Its name is based on the service name and the directory name of the docker-compose.yml file. ```bash $ pwd /tmp/docker-example/compose1 $ docker-compose up -d Creating network "compose1_default" with the default driver Creating compose1_service1_1 ... done ``` ### Second docker compose file ```yaml version: '3' services: service2: image: busybox command: sleep infinity ``` Starting services in a second docker compose file, we see the same behavior. A new default network is created and used. ```bash $ pwd /tmp/docker-example/compose2 $ docker-compose up -d Creating network "compose2_default" with the default driver Creating compose2_service2_1 ... done ``` A side-effect of these isolated networks are that the containers are unable to ping one another by service name or container name. ### Test: From Service 1 ping Service 2 ```bash # By service name $ docker exec -it compose1_service1_1 ping service2 ping: bad address 'service2' # By container name $ docker exec -it compose1_service1_1 ping compose2_service2_1 ping: bad address 'compose2_service2_1' ``` ### Test: Service 2 ping Service 1 ```bash # By service name $ docker exec -it compose2_service2_1 ping service1 ping: bad address 'service1' # By container name $ docker exec -it compose2_service2_1 ping compose1_service1_1 ping: bad address 'compose1_service1_1' ``` ## 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 `. -- where `` can be a single string without spaces. ### Creating the network ```bash $ docker network create external-example 2af4d92c2054e9deb86edaea8bb55ecb74f84a62aec7614c9f09fee386f248a6 ``` ### Modified first docker-compose file with network configured ```yaml version: '3' services: service1: image: busybox command: sleep infinity networks: default: external: name: external-example ``` Restarting the services ```bash $ pwd /tmp/docker-example/compose1 $ docker-compose up -d Creating compose1_service1_1 ... done ``` ### Modified second docker-compose file with network configured ```yaml version: '3' services: service2: image: busybox command: sleep infinity networks: default: external: name: external-example ``` Restarting the services ```bash $ 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. ```bash $ 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 ```bash # 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 ```bash # 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 ``` > As a note, you can configure your services to use a custom container name by declaring the `container_name` key under each service (i.e., at the same level as `image`). > > [Link to Docker-compose docs - container\_name](https://docs.docker.com/compose/compose-file/#container_name) ## Takeaway You can connect services defined across multiple docker-compose.yml files. In order to do this you’ll need to: 1. Create an external network with `docker network create ` 2. In each of your docker-compose.yml configure the default network to use your externally created network with the `networks` top-level key. 3. You can use either the service name or container name to connect between containers.