Change to set the container network MTU

This change adds the container network MTU option within the container
network LXC config file. This will allow a deployer to set the MTU within
a provider networks entry in openstack_user_config.yml.

Example:

  ....
  provider_networks:
    - network:
        container_bridge: "br-storage"
        container_type: "veth"
        container_interface: "eth2"
        ip_from_q: "storage"
        type: "raw"
        container_mtu: "9000"
        group_binds:
          - glance_api
          - cinder_api
          - cinder_volume
          - nova_compute
          - swift_proxy

This changes gives the deployer the ability to selectively set the mtu as
needed.

The dynamic_inventory.py script has been updated to allow for the MTU entry.

Example file documentation has been added to show how to use this new setting.

BackportPotential
DocImpact
Closes-Bug: #1477346

Change-Id: If8c0ee042d2f1322f8322ea6c8ee33606070d880

etc/openstack_deploy/openstack_user_config.yml.example

@@ -147,6 +147,9 @@
 #       Name of mechanism that connects interfaces in containers to the bridge
 #       on target hosts for this network. Typically 'veth'.
 #
+#       Option: container_mtu (optional, string)
+#       Sets the MTU within LXC for a given network type.
+#
 #       Option: ip_from_q (optional, string)
 #       Name of network in 'cidr_networks' level to use for IP address pool. Only
 #       valid for 'raw' and 'vxlan' types.
@@ -226,6 +229,7 @@
 #         container_bridge: "br-storage"
 #         container_type: "veth"
 #         container_interface: "eth2"
+#         container_mtu: "9000"
 #         ip_from_q: "storage"
 #     - network:
 #         group_binds:
@@ -233,6 +237,7 @@
 #         container_bridge: "br-vxlan"
 #         container_type: "veth"
 #         container_interface: "eth10"
+#         container_mtu: "9000"
 #         ip_from_q: "tunnel"
 #         type: "vxlan"
 #         range: "1:1000"

playbooks/inventory/dynamic_inventory.py

@@ -456,8 +456,9 @@ def _load_optional_q(config, cidr_name):
 
 
 def _add_additional_networks(key, inventory, ip_q, q_name, netmask, interface,
-                             bridge, net_type, user_config, is_ssh_address,
-                             is_container_address, static_routes):
+                             bridge, net_type, net_mtu, user_config,
+                             is_ssh_address, is_container_address,
+                             static_routes):
     """Process additional ip adds and append then to hosts as needed.
 
     If the host is found to be "is_metal" it will be marked as "on_metal"
@@ -492,6 +493,9 @@ def _add_additional_networks(key, inventory, ip_q, q_name, netmask, interface,
         if net_type:
             _network['type'] = net_type
 
+        if net_mtu:
+            _network['mtu'] = net_mtu
+
         return _network
 
     def return_netmask():
@@ -519,6 +523,7 @@ def _add_additional_networks(key, inventory, ip_q, q_name, netmask, interface,
                 interface,
                 bridge,
                 net_type,
+                net_mtu,
                 user_config,
                 is_ssh_address,
                 is_container_address,
@@ -694,6 +699,7 @@ def container_skel_load(container_skel, inventory, config):
                     interface=p_net['container_interface'],
                     bridge=p_net['container_bridge'],
                     net_type=p_net.get('container_type'),
+                    net_mtu=p_net.get('container_mtu'),
                     user_config=config,
                     is_ssh_address=p_net.get('is_ssh_address'),
                     is_container_address=p_net.get('is_container_address'),

playbooks/roles/lxc_container_create/templates/container-interface.ini.j2

@@ -10,3 +10,6 @@ lxc.network.link = {{ item.value.bridge }}
 lxc.network.hwaddr = 00:16:3e:xx:xx:xx
 # enable the device on boot
 lxc.network.flags = up
+# Set the container network MTU
+lxc.network.mtu = {{ item.value.mtu|default('1500') }}
+