Add new configuration option live_migration_scheme

This change adds a new configuration option to change scheme that is used
for live migrations. The change also deprecates old live_migration_uri
in favor of two other flags:

* live_migraton_inbound_addr to configure live migration target URI
* live_migration_scheme to change scheme used for live migration

The new configuration option does not break backward compatibility as
it does not override scheme set in live_migration_uri.

Change-Id: I38b3d1d42b2ffc4a2f6d7398061829d3c745b9a1

nova/conf/libvirt.py

@@ -259,6 +259,13 @@ Possible values:
     # TODO(hieulq): change to URIOpt for validating schemas with next release
     # of oslo_config.
     cfg.StrOpt('live_migration_uri',
+               deprecated_for_removal=True,
+               deprecated_since="15.0.0",
+               deprecated_reason="""
+live_migration_uri is deprecated for removal in favor of two other options that
+allow to change live migration scheme and target URI: ``live_migration_scheme``
+and ``live_migration_inbound_addr`` respectively.
+""",
                help="""
 Live migration target URI to use.
 
@@ -277,6 +284,23 @@ Related options:
 * ``live_migration_inbound_addr``: If ``live_migration_inbound_addr`` value
   is not None, the ip/hostname address of target compute node is used instead
   of ``live_migration_uri`` as the uri for live migration.
+* ``live_migration_scheme``: If ``live_migration_uri`` is not set, the scheme
+  used for live migration is taken from ``live_migration_scheme`` instead.
+"""),
+    cfg.StrOpt('live_migration_scheme',
+               help="""
+Schema used for live migration.
+
+Override the default libvirt live migration scheme (which is dependant on
+virt_type). If this option is set to None, nova will automatically choose a
+sensible default based on the hypervisor. It is not recommended that you change
+this unless you are very sure that hypervisor supports a particular scheme.
+
+Related options:
+* ``virt_type``: This option is meaningful only when ``virt_type`` is set to
+  `kvm` or `qemu`.
+* ``live_migration_uri``: If ``live_migration_uri`` value is not None, the
+  scheme used for live migration is taken from ``live_migration_uri`` instead.
 """),
     cfg.BoolOpt('live_migration_tunnelled',
                 default=False,

nova/tests/unit/virt/libvirt/test_driver.py

@@ -7825,6 +7825,21 @@ class LibvirtConnTestCase(test.NoDBTestCase):
             drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
             self.assertEqual(forced_uri % dest, drvr._live_migration_uri(dest))
 
+    def test_live_migration_scheme(self):
+        self.flags(live_migration_scheme='ssh', group='libvirt')
+        dest = 'destination'
+        uri = 'qemu+ssh://%s/system'
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
+        self.assertEqual(uri % dest, drvr._live_migration_uri(dest))
+
+    def test_live_migration_scheme_does_not_override_uri(self):
+        forced_uri = 'qemu+ssh://%s/system'
+        self.flags(live_migration_uri=forced_uri, group='libvirt')
+        self.flags(live_migration_scheme='tcp', group='libvirt')
+        dest = 'destination'
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
+        self.assertEqual(forced_uri % dest, drvr._live_migration_uri(dest))
+
     def test_migrate_uri(self):
         hypervisor_uri_map = (
             ('xen', None),

nova/virt/libvirt/driver.py

@@ -684,15 +684,25 @@ class LibvirtDriver(driver.ComputeDriver):
         # Only Xen and QEMU support live migration, see
         # https://libvirt.org/migration.html#scenarios for reference
         uris = {
-            'kvm': 'qemu+tcp://%s/system',
-            'qemu': 'qemu+tcp://%s/system',
+            'kvm': 'qemu+%s://%s/system',
+            'qemu': 'qemu+%s://%s/system',
             'xen': 'xenmigr://%s/system',
         }
         virt_type = CONF.libvirt.virt_type
-        uri = CONF.libvirt.live_migration_uri or uris.get(virt_type)
+        # TODO(pkoniszewski): Remove fetching live_migration_uri in Pike
+        uri = CONF.libvirt.live_migration_uri
+        if uri:
+            return uri % dest
+
+        uri = uris.get(virt_type)
         if uri is None:
             raise exception.LiveMigrationURINotAvailable(virt_type=virt_type)
-        return uri % dest
+
+        str_format = (dest,)
+        if virt_type in ('kvm', 'qemu'):
+            scheme = CONF.libvirt.live_migration_scheme or 'tcp'
+            str_format = (scheme, dest)
+        return uris.get(virt_type) % str_format
 
     @staticmethod
     def _migrate_uri(dest):

releasenotes/notes/deprecate_live_migration_uri-8ae6656664db5ba0.yaml

@@ -0,0 +1,13 @@
+---
+deprecations:
+  - |
+    The ``live_migration_uri`` option in the [libvirt] configuration section
+    is deprecated, and will be removed in a future release. The
+    ``live_migration_scheme`` should be used to change scheme used for live
+    migration, and ``live_migration_inbound_addr`` should be used to change
+    target URI.
+features:
+  - |
+    The libvirt driver now has a ``live_migration_scheme`` configuration
+    option which should be used where the ``live_migration_uri`` would
+    previously have been configured with non-default scheme.