When using custom networks in Docker like
networks: default: external: name: service-tier
And try to run that, I´m getting the error
ERROR: Network service-tier declared as external, but could not be found. Please create the network manually using
docker network create service-tier
and try again.
Is it possible to create networks automatically with docker-compose or is there no other way than creating them manually first?
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.
If you want compose to make networks you simply do: networks: network1: network2: .. to instruct compose to make the networks. They will be named <compose-dir>-<network name> Verify the creation by using docker network ls .
When you start Docker, a default bridge network (also called bridge ) is created automatically, and newly-started containers connect to it unless otherwise specified. You can also create user-defined custom bridge networks. User-defined bridge networks are superior to the default bridge network.
When you install docker it creates three networks automatically - Bridge, Host, and None. Of which, Bridge is the default network a container gets attached to when it is run.
external
is to use an existing network. If you want compose to make networks you simply do:
networks: network1: network2:
.. to instruct compose to make the networks. They will be named <compose-dir>-<network name>
Verify the creation by using docker network ls
.
You can also override the default network or specify more properties.
networks: default: driver: bridge driver_opts: com.docker.network.driver.mtu: 1450
.. will override the default network setting MTU to 1450 (handy when the host have lower than 1500 mtu and path mtu discovery doesn't work properly). There are other bridge driver options.
external
makes more sense when you want services in two compose setups to talk to each other or you have a manually created network.
As @Grimmy correctly states, docker creates all mentioned networks, so these can be later referenced by running another compose file.
But, the defaultly generated network name is hardly practlical or robust. As it could turn out to be very long or the docker
team changes their opinion on naming strategy.
But since compose file version 3.5
(means docker-compose
version 1.18.0
) one can name the network as pleases, so the overal solution is even more robust.
Please see the following snippets demonstrating on how to achieve this:
Compose file 1
version: '3.5' services: svc-name: ... networks: - specific-network-name container_name: "exact-container-reference" ... networks: specific-network-name: external: false name: specific-network-name
Compose file 2
version: '2' services: svc-using-svc-name: ... networks: - default - specific-network-name external_links: - exact-container-reference ... networks: specific-network-name: external: true
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