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[atomic-devel] recommending Flannel (w/ vxlan backend) for atomic -- thoughts?


Internally we've been doing a little looking at projects for setting-up
overlay networks between minions in a Kubernetes cluster.  One of the
most interesting options has been Flannel (formerly Rudder).  Flannel
requires minimal configuration to slice a large subnet into a series of
smaller subnets, one per minion running flanneld.

Flannel uses a configuration stored as a JSON file in etcd.  The JSON
configuration looks a bit like this:

	"Network": "",
	"SubnetLen": 28,
	"Backend": {
		"Type":	"vxlan"

The above configuration would allow up to 16 minions to each allocate
a /28 subnet for use by their local docker daemon.  (Larger or smaller
subnets are, of course, a simple matter of configuration.)  The local
configuration information is written by flanneld to a file
under /var/run, and the info is used to pass the --bip option to docker
so that it configures its docker0 bridge appropriately.

Beyond that, the vxlan backend for flanneld on each minion creates a
vxlan tunnel endpoint and configures it to use the DOVE extensions for
routing.  The route to the larger (e.g. /24) subnet points at the vxlan
interface, so traffic to other minions is directed through it.  Such
traffic triggers L2MISS and L3MISS messages that are handled by
flanneld, directing traffic to the appropriate minions.

The result is a vxlan-based overlay network that enables connectivity
between all the minions (and their pods) with a minimal amount of
configuration required.  This seems like a powerful and usable means to
enable this communication.

Given the description above (and whatever other sources you might have
at your disposal), does anyone have any objections to using this as a
default Kubernetes networking solution in Atomic?  Or any questions
about the use of Flannel in general?


John W. Linville		Hope is a good breakfast, but it is a
linville redhat com			bad supper. -- Sir Francis Bacon

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