Flannel and multi-networks

[Sreenivas Makam]

Hi

I was trying to setup Flannel with multi-networks following the procedure here(https://github.com/coreos/flannel/blob/master/README.md)

In the original flannel single network case, /run/flannel/subnet.env and /run/flannel_docker_opts.env gets created from flanneld.service and docker uses flannel_docker_opts.env to use flannel created network. For multi-network case, as i understand, we create different subnets in /run/flannel/networks/*. What other changes are needed in flanneld.service? I assume we need to create flannel_docker_opts.env per network? Its not clear how we tell container that its part of a particular network when starting using this approach?

Thanks

Sreenivas

[eugene.y...@coreos.com]

Hi Sreenivas,

The short answer is that we haven't yet made out of the box CoreOS image work with multiple networks. You can certainly try to write the service files yourself. Here are some things to keep in mind:

1. In the multi-network case, flanneld will no longer signal systemd about its readiness ("READY=1") so you will not be using "Type=notify" anymore (this b/c there's no longer one single READY event).

2. Instead, of /run/flannel/subnet.env file, it'll create /run/flannel/networks/{network-name}.env file. You can use systemd path activation (http://www.freedesktop.org/software/systemd/man/systemd.path.html) to trigger downstream units, including having a unit to convert that .env file into /run/flannel_docker_opts.env.

3. If you're using Docker, you will either need to pick a single network for it or run multiple Docker daemons. Then, use DOCKER_HOST or "docker -H ..." to pick the daemon when running a container.

4. With rkt, you can just create multiple network conf files in /etc/rkt/net.d and use subnetFile parameter (https://github.com/appc/cni/blob/master/Documentation/flannel.md). Then use "rkt run --private-net={network-name}" to select the network.

-Eugene

[f zh]

Hi,

What's the status now? Is that possible to have one container attach to two different networks provided by flannel, in Kubernetes or Docker? 

Thank you.

Zhang Fan

[Alex Polvi]

Wanted to offer an example of how to do this on k8s:

https://github.com/coreos/kube-namespace-cni

It uses a CNI plugin to change networks based on the namespace in kubernetes.

-Alex

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