neutron-api charm has outdated MTU settings

[Tytus Kurek]

It looks like neutron-api charm has outdated MTU settings. Currently MTU can be adjusted using the "network-device-mtu" option which configures the following settings:

- "network_device_mtu", however this options is deprecated in Mitaka and does not exist in Newton at all [1-2]
- "veth_mtu", however this option is now set to 9000 by default in Mitaka and Newton [1-2]

It also looks like MTU adjustment has changed significantly in Mitaka [3]. The neutron-api charm is missing options to configure "global_physnet_mtu", "path_mtu" and "physical_network_mtus" settings.

I've just performed the following tests:

TEST 1:

- I deployed OpenStack Mitaka on Trusty with "network-device-mtu" option set to 9000 and "instance-mtu" option of neutron-gateway charm set to 8900
- I launched two instances on different compute nodes
- I observed fragmentation of traffic flowing between instances

TEST 2:

- I deployed OpenStack Mitaka on Trusty without "network-device-mtu" option set and "instance-mtu" option of neutron-gateway charm set to 8900
- I patched neutron-api charm with "global_physnet_mtu" and "path_mtu" options set to 9000
- I launched two instances on different compute nodes
- I observed no fragmentation of traffic flowing between instances

References:

[1] http://docs.openstack.org/mitaka/config-reference/networking/networking_options_reference.html
[2] http://docs.openstack.org/newton/config-reference/networking/networking_options_reference.html
[3] http://docs.openstack.org/mitaka/networking-guide/config-mtu.html

[Tytus Kurek (tkurek)]

Partial fix proposed:

https://review.openstack.org/#/c/411913/

[Corey Bryant (corey.bryant)]

Another useful link: http://docs.openstack.org/mitaka/config-reference/tables/conf-changes/neutron.html

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/411913
Committed: https://git.openstack.org/cgit/openstack/charm-neutron-api/commit/?id=491e501b062a35722ac8eaa0cc9ef317fd556583
Submitter: Jenkins
Branch: master

commit 491e501b062a35722ac8eaa0cc9ef317fd556583
Author: Tytus Kurek <email address hidden>
Date: Fri Dec 16 17:45:11 2016 +0100

    Add basic support for "global_physnet_mtu" and "path_mtu" options.

    I've added basic support for "global_physnet_mtu" and "path_mtu"
    options by allowing to configure them via charm parameters.

    Change-Id: Ia95533418ccd4b7d1b96270633193ea34b1edecb
    Partial-Bug: 1650579