Docs: Centralized logging

This patch explains where to find the logs in the rsyslog server container
as well as in each service container. It also tells deployers about the
log_hosts block in openstack_user_config.yml to add a rsyslog server or
servers.

Closes-bug: 1507388

Change-Id: I3e3a5251f302609c3b98eac790b4572107a294ff

doc/source/install-guide/ops-logging.rst

@@ -0,0 +1,24 @@
+`Home <index.html>`_ OpenStack-Ansible Installation Guide
+
+Centralized Logging
+-------------------
+
+OpenStack-Ansible will configure all instances to send syslog data to a
+container (or group of containers) running rsyslog.  The rsyslog server
+containers are specified in the ``log_hosts`` section of the
+``openstack_user_config.yml`` file.
+
+The rsyslog server container(s) have logrotate installed and configured with
+a 14 day retention.  All rotated logs are compressed by default.
+
+Finding logs
+~~~~~~~~~~~~
+
+Logs are accessible in multiple locations within an OpenStack-Ansible
+deployment:
+
+* The rsyslog server container collects logs in ``/var/log/log-storage`` within
+  directories named after the container or physical host
+* Each physical host has the logs from its service containers mounted at
+  ``/openstack/log/``
+* Each service container has its own logs stored at ``/var/log/<service_name>``

doc/source/install-guide/ops.rst

@@ -7,6 +7,7 @@ Chapter 8. Operations
 
    ops-addcomputehost.rst
    ops-galera.rst
+   ops-logging.rst
    ops-troubleshooting.rst