Flannel overlay using not recommend UDP backend

[mikelorant]

The current config for flannel is listed as using the UDP backend.

  net-conf.json: |
    {
      "Network": "100.64.0.0/10",
      "Backend": {
        "Type": "udp"
      }

According to the Flannel documentation, this should only be used for debugging.

https://github.com/coreos/flannel/blob/master/Documentation/backends.md#udp

Use UDP only for debugging if your network and kernel prevent you from using VXLAN or host-gw.

This should be changed to either vxlan or host-gw.

[matthope]

For AWS environments, the Flannel AWS VPC backend may be the preferred option -
https://github.com/coreos/flannel/blob/master/Documentation/aws-vpc-backend.md

[mikelorant]

Performance benchmark details:
http://machinezone.github.io/research/networking-solutions-for-kubernetes/

Their recommendation is host-gw.

Limitations
Keep in mind that the Amazon VPC limits the number of entries per route table to 50. If you require more routes, request a quota increase or simply switch to the VXLAN backend.
AWS VPC backend has a limit of 50 nodes, so that is not a good option.

AWS VPC backend is definitely not the right choice.

[smerrill]

The default kubenet networking functions identically to the aws-vpc backend for Flannel. If you're thinking of using that, you might as well use kubenet. host-gw is also likely not a good default choice since it will only work inside a single subnet, which I think won't work for private topology.

[arielkung]

Backend should be VXLAN. Is the recommended backend in the docs, it supports multiple subnets for private topology and has better performance than UDP.

[justinsb]

Should be fixed by #3190

[chrislovecnm]

Closing as fixed