neutron-api config for path-mtu gives false positive

[Gabriel Cocenza]

When linting a bundle generated on fce-templates it's possible to see this error:

ERROR Application neutron-api has incorrect setting for 'path-mtu': Expected 9000, got 1558

Talking with Nobuto, this is a false positive. path-mtu should be set to <= 1550 for ovs and set to <= 1558 to ovn.

SolQA will eventually update those values on BB (Bundle Builder) to differentiate ovs and ovn.

[Nobuto Murata (nobuto)]

To be more precise, it can be bigger than 1550 or 1558, but to use mtu=1500 on tenant networks, those two values are the requirement.

Using bigger value can be a problem especially with OVN when communicating with other external networks through a router because of missing:
https://bugs.launchpad.net/charm-neutron-api-plugin-ovn/+bug/1947391

[Nobuto Murata (nobuto)]

> ERROR Application neutron-api has incorrect setting for 'path-mtu': Expected 9000, got 1558
>
> Talking with Nobuto, this is a false positive. path-mtu should be set to <= 1550 for ovs and set to <= 1558 to ovn.

For the time being, the lint rule can be path-mtu >=1550 for ovs, and path-mtu >=1558 for ovn.

[Gabriel Cocenza (gabrielcocenza)]

> For the time being, the lint rule can be path-mtu >=1550 for ovs, and path-mtu >=1558 for ovn.

I've already send a patch to review that is adding two capabilities:

- set log-level
- set custom message if the check doesn't pass.

So right now the patch is sending a warning message if the path-mtu >= 1550 for ovs, and path-mtu >= 1558 for ovn. The message says:

"Application neutron-api has config for 'path-mtu' which is bigger than <PATH_MTU_VALUE>. Using bigger value can be a problem to communicate with other external networks through a router."

What do you think Nobuto?

Setting the lint rule path-mtu >= 1550 or path-matu >= 1558 would be easier, but I think it's a good feature for juju-lint be able to control custom messages and log-level.