doc/rgw: caption a diagram

Add an explanation of a diagram that shows how object data is replicated
between zones within a zonegroup.

Co-authored-by: Anthony D'Atri <anthony.datri@gmail.com>
Signed-off-by: Zac Dover <zac.dover@proton.me>
(cherry picked from commit ce2bd7cb2603c479c17ac18b9277b903a02bb06a)

diff --git a/doc/radosgw/multisite.rst b/doc/radosgw/multisite.rst
index b6db4962e9eeb32dbb838a55516ceb7434d80bc9..ca0ca462f8ea80ff5cfba4215bd8f1ec23366d9e 100644 (file)
--- a/doc/radosgw/multisite.rst
+++ b/doc/radosgw/multisite.rst
@@ -64,6 +64,19 @@ something like this:
 .. image:: ../images/zone-sync2.png
    :align: center
 
+At the top of this diagram, we see two applications (also known as "clients").
+The application on the right is both writing and reading data from the Ceph
+Cluster, by means of the RADOS Gateway (RGW).
+
+In the middle of this diagram, we see two zones, each of which contains an
+instance of a RADOS Gateway (RGW). These instances of RGW are handling the
+movement of data from the applications to the zonegroup. The arrow from the
+master zone (US-EAST) to the secondary zone (US-WEST) represents an act of data
+synchronization.
+
+At the bottom of this diagram, we see the master zonegroup that contains the
+master zone and the secondary zone.
+
 For additional details on setting up a cluster, see `Ceph Object Gateway for
 Production <https://access.redhat.com/documentation/en-us/red_hat_ceph_storage/3/html/ceph_object_gateway_for_production/index/>`__.