[jacekn,r=james-page,t=james-page] Add option to support configuration of instance MTU.

README.md

@@ -49,6 +49,14 @@ The gateway provides two key services; L3 network routing and DHCP services.
 
 These are both required in a fully functional Neutron Openstack deployment.
 
+See upstream [Neutron multi extnet](http://docs.openstack.org/trunk/config-reference/content/adv_cfg_l3_agent_multi_extnet.html)
+
+Configuration Options
+---------------------
+
+Multiple Floating Pools
+=======================
+
 If multiple floating pools are needed then an L3 agent (which corresponds to
 a quantum-gateway for the sake of this charm) is needed for each one. Each
 gateway needs to be deployed as a seperate service so that the external
@@ -70,7 +78,20 @@ network id can be set differently for each gateway e.g.
     juju set quantum-gateway-extnet1 "external-network-id=<extnet1 id>"
     juju set quantum-gateway-extnet2 "external-network-id=<extnet2 id>"
 
-See upstream [Neutron multi extnet](http://docs.openstack.org/trunk/config-reference/content/adv_cfg_l3_agent_multi_extnet.html)
+Instance MTU
+============
+
+When using Open vSwitch plugin with GRE tunnels default MTU of 1500 can cause
+packet fragmentation due to GRE overhead. One solution is to increase the MTU on
+physical hosts and network equipment. When this is not possible or practical thi
+charm's instance-mtu option can be used to reduce instance MTU via DHCP.
+
+    juju set quantum-gateway instance-mtu=1400
+
+OpenStack upstream documentation recomments a MTU value of 1400:
+[Openstack documentation](http://docs.openstack.org/admin-guide-cloud/content/openvswitch_plugin.html)
+
+Note that this option was added in Havana and will be ignored in older releases.
 
 TODO
 ----

config.yaml

@@ -50,3 +50,10 @@ options:
     type: string
     description: RabbitMQ Virtual Host
     default: openstack
+  instance-mtu:
+    type: int
+    description: |
+      Configure DHCP services to provide MTU configuration to instances
+      within the cloud.  This is useful in deployments where its not
+      possible to increase MTU on switches and physical servers to
+      accomodate the packet overhead of using GRE tunnels.

hooks/quantum_contexts.py

@@ -133,7 +133,8 @@ class QuantumGatewayContext(OSContextGenerator):
             'shared_secret': get_shared_secret(),
             'local_ip': get_host_ip(),  # XXX: data network impact
             'core_plugin': core_plugin(),
-            'plugin': config('plugin')
+            'plugin': config('plugin'),
+            'instance_mtu': config('instance-mtu')
         }
         return ctxt
 

hooks/quantum_utils.py

@@ -140,6 +140,7 @@ QUANTUM_METADATA_AGENT_CONF = "/etc/quantum/metadata_agent.ini"
 NEUTRON_CONF = "/etc/neutron/neutron.conf"
 NEUTRON_L3_AGENT_CONF = "/etc/neutron/l3_agent.ini"
 NEUTRON_DHCP_AGENT_CONF = "/etc/neutron/dhcp_agent.ini"
+NEUTRON_DNSMASQ_CONF = "/etc/neutron/dnsmasq.conf"
 NEUTRON_METADATA_AGENT_CONF = "/etc/neutron/metadata_agent.ini"
 
 NOVA_CONF = "/etc/nova/nova.conf"
@@ -172,6 +173,10 @@ NEUTRON_SHARED_CONFIG_FILES = {
         'hook_contexts': [QuantumGatewayContext()],
         'services': ['neutron-dhcp-agent']
     },
+    NEUTRON_DNSMASQ_CONF: {
+        'hook_contexts': [QuantumGatewayContext()],
+        'services': ['neutron-dhcp-agent']
+    },
     NEUTRON_METADATA_AGENT_CONF: {
         'hook_contexts': [NetworkServiceContext(),
                           QuantumGatewayContext()],
@@ -272,7 +277,6 @@ def register_configs():
     for conf in CONFIG_FILES[name][plugin]:
         configs.register(conf,
                          CONFIG_FILES[name][plugin][conf]['hook_contexts'])
-
     return configs
 
 

templates/havana/dhcp_agent.ini

@@ -1,9 +1,16 @@
+###############################################################################
+# [ WARNING ]
+# Configuration file maintained by Juju. Local changes may be overwritten.
+###############################################################################
 [DEFAULT]
 state_path = /var/lib/neutron
 interface_driver = neutron.agent.linux.interface.OVSInterfaceDriver
 dhcp_driver = neutron.agent.linux.dhcp.Dnsmasq
 root_helper = sudo /usr/bin/neutron-rootwrap /etc/neutron/rootwrap.conf
 ovs_use_veth = True
+{% if instance_mtu -%}
+dnsmasq_config_file = /etc/neutron/dnsmasq.conf
+{% endif %}
 {% if plugin == 'nvp' %}
 enable_metadata_network = True
 enable_isolated_metadata = True

templates/havana/dnsmasq.conf

@@ -0,0 +1,3 @@
+{%- if instance_mtu -%}
+dhcp-option=26,{{ instance_mtu }}
+{% endif %}

unit_tests/test_quantum_contexts.py

@@ -180,13 +180,19 @@ class TestQuantumGatewayContext(CharmTestCase):
     @patch.object(quantum_contexts, 'get_shared_secret')
     @patch.object(quantum_contexts, 'get_host_ip')
     def test_all(self, _host_ip, _secret):
-        self.config.return_value = 'ovs'
+        def side_effect(arg):
+            return_values = {'plugin': 'ovs',
+                             'instance-mtu': 1420,
+                             'openstack-origin': 'foo'}
+            return return_values[arg]
+        self.config.side_effect = side_effect
         self.get_os_codename_install_source.return_value = 'folsom'
         _host_ip.return_value = '10.5.0.1'
         _secret.return_value = 'testsecret'
         self.assertEquals(quantum_contexts.QuantumGatewayContext()(), {
             'shared_secret': 'testsecret',
             'local_ip': '10.5.0.1',
+            'instance_mtu': 1420,
             'core_plugin': "quantum.plugins.openvswitch.ovs_quantum_plugin."
                            "OVSQuantumPluginV2",
             'plugin': 'ovs'

unit_tests/test_quantum_utils.py

@@ -158,6 +158,7 @@ class TestQuantumUtils(CharmTestCase):
             quantum_utils.NEUTRON_METADATA_AGENT_CONF:
             ['neutron-metadata-agent'],
             quantum_utils.NEUTRON_DHCP_AGENT_CONF: ['neutron-dhcp-agent'],
+            quantum_utils.NEUTRON_DNSMASQ_CONF: ['neutron-dhcp-agent'],
             quantum_utils.NEUTRON_CONF: ['neutron-l3-agent',
                                          'neutron-dhcp-agent',
                                          'neutron-metadata-agent',
@@ -209,6 +210,7 @@ class TestQuantumUtils(CharmTestCase):
         self.config.return_value = 'nvp'
         ex_map = {
             quantum_utils.NEUTRON_DHCP_AGENT_CONF: ['neutron-dhcp-agent'],
+            quantum_utils.NEUTRON_DNSMASQ_CONF: ['neutron-dhcp-agent'],
             quantum_utils.NOVA_CONF: ['nova-api-metadata'],
             quantum_utils.NEUTRON_CONF: ['neutron-dhcp-agent',
                                          'neutron-metadata-agent'],