flannel does not work in Kubernetes on CentOS hosts, but works on Ubuntu hosts

[kgignatyev-inspur]

Expected Behavior

Flannel networking working fast and the same way on Ubuntu and CentoOS hosts

Current Behavior

DNS resolution works slow (via DNS service in Kubernetes) or not working at all Alpine containers with complaint about 'reply from unexpected source'

Possible Solution

--

Steps to Reproduce (for bugs)

create simple cluster with kops in us-east-2 and edit nodes and masters to use CentoOS image (AMI: ami-e0eac385) per
https://github.com/kubernetes/kops/blob/master/docs/images.md

Context

kubernetes/kops#4040

Your Environment

• Flannel version:
• Backend used (e.g. vxlan or udp): vxlan
• Etcd version:
• Kubernetes version (if used):1.8.5
• Operating System and version: CentoOS 7
• Link to your project (optional):

More details in the original issue:
kubernetes/kops#4040

[rajatchopra]

Resolve it by running:

$ modprobe br_netfilter
$ sysctl -w net.bridge.bridge-nf-call-iptables = 1