neutron-db-manage: add has_offline_migrations command to doc

Add the has_offline_migrations command to the networking-guide.
This patch has to add documentation for the neutron-db-manage
tool as well.

Change-Id: Ic210f761ff0a56008c49eeb89e6fcf5b9aae6810
Closes-Bug: #1537348
Related-Bug: #1519118

doc/networking-guide/source/migration-neutron-database.rst

@@ -0,0 +1,143 @@
+==================
+Database migration
+==================
+
+The upgrade of the Networking service database is implemented with Alembic
+migration chains. The migrations in the ``alembic/versions`` contain the
+changes needed to migrate from older Networking service releases to newer ones.
+
+Since Liberty, Networking maintains two parallel Alembic migration branches.
+
+The first branch is called expand and is used to store expansion-only
+migration rules. These rules are strictly additive and can be applied while the
+Neutron server is running.
+
+The second branch is called contract and is used to store those migration
+rules that are not safe to apply while Neutron server is running.
+
+The intent of separate branches is to allow invoking those safe migrations
+from the expand branch while the Neutron server is running and therefore
+reducing downtime needed to upgrade the service.
+
+A database management command-line tool uses the Alembic library to manage the
+migration.
+
+Database management command-line tool
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The database management command-line tool is called
+:command:`neutron-db-manage`. Pass the :option:`--help` option to the tool for
+usage information.
+
+The tool takes some options followed by some commands:
+
+.. code-block:: console
+
+   $ neutron-db-manage <options> <commands>
+
+The tool needs to access the database connection string, which is provided in
+the ``neutron.conf`` configuration file in an installation. The tool
+automatically reads from ``/etc/neutron/neutron.conf`` if it is present.
+If the configuration is in a different location, use the following command:
+
+.. code-block:: console
+
+   $ neutron-db-manage --config-file /path/to/neutron.conf <commands>
+
+Multiple :option:`--config-file` options can be passed if needed.
+
+Instead of reading the DB connection from the configuration file(s), you can
+use the :option:`--database-connection` option:
+
+.. code-block:: console
+
+   $ neutron-db-manage --database-connection
+     mysql+pymysql://root:secret@127.0.0.1/neutron?charset=utf8 <commands>
+
+The `branches`, `current`, and `history` commands all accept a
+:option:`--verbose` option, which, when passed, will instruct
+:command:`neutron-db-manage` to display more verbose output for the specified
+command:
+
+.. code-block:: console
+
+   $ neutron-db-manage current --verbose
+
+.. note::
+
+   The tool usage examples below do not show the options. It is assumed that
+   you use the options that you need for your environment.
+
+In new deployments, you start with an empty database and then upgrade to
+the latest database version using the following command:
+
+.. code-block:: console
+
+   $ neutron-db-manage upgrade heads
+
+After installing a new version of the Neutron server, upgrade the database
+using the following command:
+
+.. code-block:: console
+
+   $ neutron-db-manage upgrade heads
+
+In existing deployments, check the current database version using the
+following command:
+
+.. code-block:: console
+
+   $ neutron-db-manage current
+
+To apply the expansion migration rules, use the following command:
+
+.. code-block:: console
+
+   $ neutron-db-manage upgrade --expand
+
+To apply the non-expansive migration rules, use the following command:
+
+.. code-block:: console
+
+   $ neutron-db-manage upgrade --contract
+
+To check if any contract migrations are pending and therefore if offline
+migration is required, use the following command:
+
+.. code-block:: console
+
+   $ neutron-db-manage has_offline_migrations
+
+.. note::
+
+   Offline migration requires all Neutron server instances in the cluster to
+   be shutdown before you apply any contract scripts.
+
+To generate a script of the command instead of operating immediately on the
+database, use the following command:
+
+.. code-block:: console
+
+   $ neutron-db-manage upgrade heads --sql
+
+   .. note::
+
+      The `--sql` option causes the command to generate a script.  The script
+      can be run later (online or offline), perhaps after verifying and/or
+      modifying it.
+
+To migrate between specific migration versions, use the following command:
+
+.. code-block:: console
+
+   $ neutron-db-manage upgrade <start version>:<end version>
+
+To upgrade the database incrementally, use the following command:
+
+.. code-block:: console
+
+   $ neutron-db-manage upgrade --delta <# of revs>
+
+.. note::
+
+   Database downgrade is not supported.

doc/networking-guide/source/migration.rst

@@ -5,6 +5,7 @@ Migration
 .. toctree::
    :maxdepth: 2
 
+   migration-neutron-database.rst
    migration-nova-network-to-neutron.rst
    migration-classic-to-dvr.rst
    migration-classic-to-l3ha.rst