Authoritative Documentation for Multus and Flannel Integration in K3s

[auphof]

I'm relatively new to K3s and have encountered challenges while trying to integrate Multus with Flannel, it just works in microk8s enable multus. For K3s this was not easy, After an exhaustive search through articles, Gists, and other resources—which often seemed outdated—I found a helpful response on RancherSlack that led me to a solution. This experience highlighted a gap in the current K3s documentation regarding the integration of Multus. Ideally It should be as simple as in microk8s or some clear documentation

Describe the solution you'd like https://docs.k3s.io/installation/network-options#custom-cni documents other CNI implementations, I would like to see this expanded on how to integrate multus with flannel, or as simple addon implementation as in microk8s

Describe alternatives you've considered

1. I note that this has come up before #2163 (Now Closed) in response to the 2020 decision, current docs do show Canal, Callico, Cillum support.

2. There is a ticket https://github.com/k3s-io/docs/issues/194 to better organize content for network config, any created docs for Flannel with Multus would migrate to any proposed enhanced layout.

3. @brandond mentioned in https://rancher-users.slack.com/archives/CGGQEHPPW/p1707194893561179?thread_ts=1707193339.500079&cid=CGGQEHPPW that a flannel maintainer has a simplified solution deploy multus with the integrated flannel. It can be done without disabling it and installing flannel separately this would be 🚀

Additional context for the moment i propose adding to Custom CNI inline with this mockup. I a willing to raise a PR in https://github.com/k3s-io/docs to capture this current working method

[brandond]

cc @manuelbuil

[manuelbuil]

If time allows, I'd like to integrate multus+whereabouts in k3s for the March release. But any docs are super welcome!

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