Today I Learned: Docker Compose Networks
Due to a bug fix or maybe a new feature to Docker Compose, I caught myself yak shaving how Docker and Docker Compose handle local networking.
I have 2 services, let’s call them
bar-service. They both live in their respective directories as siblings.
. ├── bar-service │ ├── docker-compose.yml │ └── src └── foo-service ├── docker-compose.yml └── src
bar-service refers to
foo-service’s network like so:
# bar-service/docker-compose.yml networks: default: external: name: fooservice_default
The Yak Shave
By default Compose sets up a single network for your app. Each container for a service joins the default network and is both reachable by other containers on that network, and discoverable by them at a hostname identical to the container name.
As of docker-compose 1.21.0:
Dashes and underscores in project names are no longer stripped out.
This means that the
docker-compose.yml file above for
bar-service needs the network name for
foo-service updated to add back in the stripped dashes.
# bar-service/docker-compose.yml networks: default: external: name: foo-service_default
As of Docker Compose file format version 3.5, the network name can be explicitly defined as described in Specify custom networks.
# foo-service/docker-compose.yml version: "3.5" networks: default: name: fooservice
And the original external network configuration file for
bar-service would now work, referencing the network of