Ussuri/OVN Telegraf flooding the kernel log with version negotiation failed messages

[Márton Kiss]

Bionic/Ussuri/OVN cloud, HOV 20.08, the telegraf running on compute nodes are flooding the syslog with "version negotiation failed" message, causing a large amount of log entries to be processed by graylog / elasticsearch (40k/hour).

Nov 9 08:14:20 <hostname> ovs-ofctl: ovs|00001|vconn|WARN|unix:/var/run/openvswitch/br-int.mgmt: version negotiation failed (we support version 0x01, peer supports versions 0x04, 0x06)
Nov 9 08:14:30 <hostname> ovs-ofctl: ovs|00001|vconn|WARN|unix:/var/run/openvswitch/br-int.mgmt: version negotiation failed (we support version 0x01, peer supports versions 0x04, 0x06)
Nov 9 08:14:40 <hostname> ovs-ofctl: ovs|00001|vconn|WARN|unix:/var/run/openvswitch/br-int.mgmt: version negotiation failed (we support version 0x01, peer supports versions 0x04, 0x06)
Nov 9 08:14:50 <hostname> ovs-ofctl: ovs|00001|vconn|WARN|unix:/var/run/openvswitch/br-int.mgmt: version negotiation failed (we support version 0x01, peer supports versions 0x04, 0x06)

The telgraf charm periodically retrieves OVS flow information using ovs-ofctl command [1]. The openflow version is not mentioned in the command which leads to the warnings on ovs-vswitchd.

The fix should include a proper openflow version for the ovs-ofctl command using the -O option.

A brigde's supported OpenFlow version can be retrieved using:
ovs-vsctl find bridge name=br-int | grep protocols
protocols : [OpenFlow13, OpenFlow15]

The telegraf-38 and telegraf-39 stable charms, master branch seems to be affected in case of an OVN deployment.

[1] https://git.launchpad.net/charm-telegraf/tree/src/files/telegraf_exec_metrics.py#n364

[Hemanth Nakkina (hemanth-n)]

MR for code review: https://code.launchpad.net/~hemanth-n/charm-telegraf/+git/charm-telegraf/+merge/394920