[FEATURE] Support custom options for docker network

[lsoica]

Scope of your request

Add the ability to provide custom options for docker network create.

As k3d creates its own docker network, the network uses default MTU (1500).
In some environments, like OpenStack, configured with VxLAN, the host is already configured with a lower MTU (1450) so we need a way to provide a custom MTU for the docker network.

Describe the solution you'd like

An extra option for k3d create, like:
k3d create --docker-network-opt "com.docker.network.driver.mtu=1450" --docker-network-opt another-value

[iwilltry42]

Hi there, thanks for this issue 👍
We're currently working on a --network flag which skips the creation of a new cluster network and just attaches the containers to an existing network. Would that be sufficient?

[lsoica]

Hi,

Yes, thanks, works for my use case.

[iwilltry42]

Great, closing in favor of #220

[AntonOfTheWoods]

Hi @iwilltry42 , it doesn't really work for my usecase... is there no way to tell k3d docker to create a different mtu size? Is the only way to create my own pre-existing network?

[iwilltry42]

Hey @AntonOfTheWoods unfortunately it would be really cumbersome to expose all possible options for docker network creation via k3d. We're currently only exposing the choice of a subnet to use.
For all the rest, it's just way more flexible to do docker network create [OPTIONS] NAME and then do k3d cluster create --network NAME.
May I ask what usecase this doesn't work for for you?

[AntonOfTheWoods]

@iwilltry42 genuine brainfart, sorry. I have some generic scripts and didn't want it to be specific to docker (vs podman) but that was just being dumb. It is actually fine.

I did notice that if you create using the name it would have created anyway, it will use it without you explicitly specifying it (with a warning). That tripped me up because for some reason when I was deleting the cluster it, wasn't deleting the automatically created network. As such my if not network_exists wasn't creating a new mtu-ed network.

I guess it is pretty obvious what is happening after a couple of minutes though, so probably not worth adding to the docs. Thanks again, k3d is truly the most awesome way to develop stuff for kube!

[iwilltry42]

Great, thanks for the feedback! :)