Live Migration sequence diagram

Based on mriedem's hand-drawn version [1] (but not as pretty).

[1] https://photos.google.com/share/AF1QipNpWVQKU8GK4_9wxVbiRJUqJnMzqPcBh6DvjVyBPIjjmi6ZU8r9TleQNo6pV1t9SA?key=NUl3OUFGYkRFTE8tMHhSX0lfc0Y1eEdoeHo4SUhn

Co-Authored-By: Matt Riedemann <mriedem.os@gmail.com>

Change-Id: I63046079cd3135b4b19c0c6745075f090d04e396

doc/source/conf.py

@@ -46,6 +46,7 @@ extensions = ['sphinx.ext.autodoc',
               'ext.versioned_notifications',
               'ext.feature_matrix',
               'sphinxcontrib.actdiag',
+              'sphinxcontrib.seqdiag',
               ]
 
 # openstackdocstheme options
@@ -62,6 +63,9 @@ sample_policy_basename = '_static/nova'
 actdiag_html_image_format = 'SVG'
 actdiag_antialias = True
 
+seqdiag_html_image_format = 'SVG'
+seqdiag_antialias = True
+
 todo_include_todos = True
 
 # The suffix of source filenames.

doc/source/index.rst

@@ -261,6 +261,7 @@ looking parts of our architecture. These are collected below.
    reference/api-microversion-history.rst
    reference/gmr
    reference/i18n
+   reference/live-migration
    reference/notifications
    reference/policy-enforcement
    reference/rpc

doc/source/reference/index.rst

@@ -13,6 +13,7 @@ The following is a dive into some of the internals in nova.
 
 * :doc:`/reference/rpc`: How nova uses AMQP as an RPC transport
 * :doc:`/reference/scheduling`: The workflow through the scheduling process
+* :doc:`/reference/live-migration`: The live migration flow
 * :doc:`/reference/services`: Module descriptions for some of the key modules
   used in starting / running services
 * :doc:`/reference/vm-states`: Cheat sheet for understanding the life cycle of

doc/source/reference/live-migration.rst

@@ -0,0 +1,47 @@
+..
+      Licensed under the Apache License, Version 2.0 (the "License"); you may
+      not use this file except in compliance with the License. You may obtain
+      a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+      License for the specific language governing permissions and limitations
+      under the License.
+
+================
+ Live Migration
+================
+
+.. seqdiag::
+
+    seqdiag {
+        Conductor; Source; Destination;
+        edge_length = 300;
+        span_height = 15;
+        activation = none;
+        default_note_color = white;
+
+        Conductor            ->  Destination [label = "call", note = "check_can_live_migrate_destination"];
+                      Source <-  Destination [label = "call", leftnote = "check_can_live_migrate_source"];
+                      Source --> Destination;
+        Conductor            <-- Destination;
+
+        Conductor ->> Source [label = "cast", note = "live_migrate"];
+                      Source ->  Destination [label = "call", note = "pre_live_migration (set up dest)"];
+                      Source <-- Destination;
+
+        === driver.live_migration (success) ===
+
+                      Source ->  Source [leftnote = "post_live_migration (clean up source)"];
+                      Source ->  Destination [label = "call", note = "post_live_migration_at_destination (finish dest)"];
+                      Source <-- Destination;
+
+        === driver.live_migration (failure) ===
+
+                      Source ->  Destination [label = "call", note = "remove_volume_connections"];
+                      Source <-- Destination;
+                      Source ->> Destination [label = "cast", note = "rollback_live_migration_at_destination"];
+    }

test-requirements.txt

@@ -16,6 +16,7 @@ python-subunit>=0.0.18 # Apache-2.0/BSD
 requests-mock>=1.1.0 # Apache-2.0
 sphinx>=1.6.2 # BSD
 sphinxcontrib-actdiag>=0.8.5 # BSD
+sphinxcontrib-seqdiag>=0.8.4 # BSD
 os-api-ref>=1.4.0 # Apache-2.0
 oslotest>=1.10.0 # Apache-2.0
 os-testr>=1.0.0 # Apache-2.0