Document single process Ironic

Change-Id: I2e60d989e7e3717510a8be2832db8a64ceac892e
Story: #2009676
Task: #44120

doc/source/install/include/configure-ironic-singleprocess.inc

@@ -0,0 +1,48 @@
+Configuring single-process ironic
+---------------------------------
+
+As an alternative to starting separate API and conductor instances, you can
+start ``ironic`` services that combine an API and a conductor in the same
+process. This may be particularly beneficial in environments with limited
+resources and low number of nodes to handle.
+
+.. note:: This feature is available starting with the Yoga release series.
+
+#. Start with setting up the environment as described in both `Configuring
+   ironic-api service`_ and `Configuring ironic-conductor service`_, but do not
+   start any services. Merge configuration options into a single configuration
+   file.
+
+   .. note::
+      Any RPC settings will only take effect if you have more than one combined
+      service started or if you have additional conductors.
+
+      If you don't plan to have more than one conductor, you can disable the
+      RPC completely:
+
+      .. code-block:: ini
+
+        [DEFAULT]
+        rpc_transport = none
+
+#. Stop existing services if they are already started:
+
+   Fedora/RHEL/CentOS/SUSE::
+
+       sudo systemctl stop openstack-ironic-api
+       sudo systemctl stop openstack-ironic-conductor
+
+   Ubuntu::
+
+       sudo service ironic-api stop
+       sudo service ironic-conductor stop
+
+#. Start or restart the ironic service:
+
+   Fedora/RHEL8/CentOS8/SUSE::
+
+       sudo systemctl restart openstack-ironic
+
+   Ubuntu::
+
+       sudo service ironic restart

doc/source/install/install-obs.rst

@@ -37,3 +37,5 @@ Install and configure components
 .. include:: include/configure-ironic-api-mod_wsgi.inc
 
 .. include:: include/configure-ironic-conductor.inc
+
+.. include:: include/configure-ironic-singleprocess.inc

doc/source/install/install-rdo.rst

@@ -33,3 +33,5 @@ Install and configure components
 .. include:: include/configure-ironic-api-mod_wsgi.inc
 
 .. include:: include/configure-ironic-conductor.inc
+
+.. include:: include/configure-ironic-singleprocess.inc

doc/source/install/install-ubuntu.rst

@@ -29,3 +29,5 @@ Install and configure components
 .. include:: include/configure-ironic-api-mod_wsgi.inc
 
 .. include:: include/configure-ironic-conductor.inc
+
+.. include:: include/configure-ironic-singleprocess.inc