From 28fff3f92d09737a2db0c98c590b7698917c2095 Mon Sep 17 00:00:00 2001
From: Guillaume Boutry <guillaume.boutry@canonical.com>
Date: Mon, 6 May 2024 11:11:21 +0200
Subject: [PATCH] [neutron-k8s] Add MTU configuration options

Add the following options to neutron-k8s:
- global-physnet-mtu: set the global MTU for networks
- path-mtu: MTU for overlay/tunnel network
- physical-network-mtus: if using multiple physical networks with
  different MTUs

Change-Id: I305c0570072ad7e3e7cf1e09b8998ca3f8bcc9fb
---
 charms/neutron-k8s/config.yaml                | 27 +++++++++++++++++++
 charms/neutron-k8s/src/charm.py               |  1 -
 .../neutron-k8s/src/templates/ml2_conf.ini.j2 |  5 +++-
 .../neutron-k8s/src/templates/neutron.conf.j2 |  2 +-
 4 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/charms/neutron-k8s/config.yaml b/charms/neutron-k8s/config.yaml
index 86ada93a..f52c3e7d 100644
--- a/charms/neutron-k8s/config.yaml
+++ b/charms/neutron-k8s/config.yaml
@@ -46,3 +46,30 @@ options:
     default: False
     description: Enable IGMP snooping for integration bridge.
     type: boolean
+  global-physnet-mtu:
+    type: int
+    default: 1500
+    description: |
+      MTU of the underlying physical network. Neutron uses this value to
+      calculate MTU for all virtual network components. For flat and
+      VLAN networks, neutron uses this value without modification. For
+      overlay networks such as VXLAN, neutron automatically subtracts
+      the overlay protocol overhead from this value.
+  path-mtu:
+    type: int
+    default: 1500
+    description: |
+      Maximum size of an IP packet (MTU) that can traverse the
+      underlying physical network infrastructure without fragmentation
+      when using an overlay/tunnel protocol. This option allows
+      specifying a physical network MTU value that differs from the
+      default global-physnet-mtu value.
+  physical-network-mtus:
+     type: string
+     default:
+     description: |
+      Space-delimited list of <physical_network>:<mtu> pairs specifying MTU for
+      individual physical networks.
+      .
+      Use this if a subset of your flat or VLAN provider networks have a MTU
+      that differ with what is set in global-physnet-mtu.
diff --git a/charms/neutron-k8s/src/charm.py b/charms/neutron-k8s/src/charm.py
index 13119535..b4809720 100755
--- a/charms/neutron-k8s/src/charm.py
+++ b/charms/neutron-k8s/src/charm.py
@@ -241,7 +241,6 @@ class OVNContext(sunbeam_ctxts.ConfigContext):
             "type_drivers": "geneve,gre,vlan,flat,local",
             "tenant_network_types": "geneve,gre,vlan,flat,local",
             "mechanism_drivers": "ovn",
-            "path_mtu": "1500",
             "tunnel_id_ranges": "1:1000",
             "vni_ranges": "1001:2000",
             "flat_networks": "physnet1",
diff --git a/charms/neutron-k8s/src/templates/ml2_conf.ini.j2 b/charms/neutron-k8s/src/templates/ml2_conf.ini.j2
index f77d4b88..9c808dc6 100644
--- a/charms/neutron-k8s/src/templates/ml2_conf.ini.j2
+++ b/charms/neutron-k8s/src/templates/ml2_conf.ini.j2
@@ -8,7 +8,10 @@ type_drivers = {{ ovn.type_drivers }}
 tenant_network_types = {{ ovn.tenant_network_types }}
 mechanism_drivers = {{ ovn.mechanism_drivers }}
 
-path_mtu = {{ ovn.path_mtu }}
+path_mtu = {{ options.path_mtu }}
+{% if options.physical_network_mtus %}
+physical_network_mtus = {{ options.physical_network_mtus.split(' ') | join(',') }}
+{% endif %}
 
 [ml2_type_gre]
 tunnel_id_ranges = {{ ovn.tunnel_id_ranges }}
diff --git a/charms/neutron-k8s/src/templates/neutron.conf.j2 b/charms/neutron-k8s/src/templates/neutron.conf.j2
index b9940467..b589ba68 100644
--- a/charms/neutron-k8s/src/templates/neutron.conf.j2
+++ b/charms/neutron-k8s/src/templates/neutron.conf.j2
@@ -24,7 +24,7 @@ notify_nova_on_port_data_changes = True
 
 dns_domain = {{ options.dns_domain }}
 
-global_physnet_mtu = 1500
+global_physnet_mtu = {{ options.global_physnet_mtu }}
 
 transport_url = {{ amqp.transport_url }}