support container network aliases

[tmds]

Allow to set network aliases for containers.

Either providing the alias on docker run:

docker run --name container1 --network network1 --network-alias alias1 --network-alias alias2 <image>

Or providing the alias post docker run:

network connect --alias alias1 --alias alias2 network1 container1

[rhatdan]

@baude This looks like something that the dns-CNI PLugin would need to handle?

[baude]

nope, i dont think so. in fact, i dont think we can do this with our current container architecture. @mheon do I remember that correctly?

[mheon]

I think we can but it would be a fair amount of effort to get it working - maybe a week or two of time for me or someone else who knows the network code well.

[mheon]

Also, there's going to be an unavoidable connection drop when we do add the new network, I think (we basically need to have CNI tear down and then recreate the network)

[tmds]

My use for podman network connect is to be able to pass an --alias.
docker also supports it via a --network-alias argument on the run command.
@mheon probably this is simpler to implement? Should I change this issue for adding that argument to podman?

[mheon]

I would say that aliases are more difficult to implement than network connect right now (still possible, but probably a good sprint worth of work to implement)

[rhatdan]

Of course if the community wanted to work on a PR, we would love to see it.

[tmds]

Without podman network connect --alias, or podman run --network-alias all container dns names share the same namespace. It is not possible to use the same network name for containers that live on different networks, because they clash as container names.

@rhatdan I hope someone takes this on, unfortunately I can't volunteer because I don't speak any go.

[mheon]

Are you sure about that? I'm fairly certain that we run per-network DNS instances, so we effectively namespace container names by the network they're attached to? @baude can confirm.

[tmds]

The clash is at the container name level:

$ podman network create net1
$ podman network create net2
$ podman run --rm -d --name name1 --network net1 busybox sleep 10
$ podman run --rm --name name1 --network net2 busybox sleep 10
Error: error creating container storage: the container name "name1" is already in use by "650f7d2d299dfe23d05e5f1a2cadc4230841fd33eec5bae3d9be9da05d2b1ee3". You have to remove that container to be able to reuse that name.: that name is already in use

[rhatdan]

Would --hostname fix this?

[tmds]

Would --hostname fix this?

I tried that. This sets the hostname for the host itself. It isn't added as a name to the DNS so other containers can resolve it.

[tmds]

For my use-case either of these could work:

Providing the alias on docker run:

docker run --name container1 --network network1 --network-alias alias1 --network-alias alias2 <image>

Providing the alias post docker run:

network connect --alias alias1 --alias alias2 network1 container1