doc/mgr/dashboard: update dashboard docs to reflect new defaults

doc/mgr/dashboard.rst

@@ -2,29 +2,50 @@ dashboard plugin
 ================
 
 Dashboard plugin visualizes the statistics of the cluster using a web server
-hosted by ``ceph-mgr``. Like most web applications, dashboard binds to a host
-name and port. Since each ``ceph-mgr`` hosts its own instance of dashboard, we
-need to configure them separately. The hostname and port are stored using the
-configuration key facility. So we can configure them like::
+hosted by ``ceph-mgr``.
+
+Enabling
+--------
+
+The *dashboard* module is enabled with::
+
+  ceph mgr module enable dashboard
+
+Configuration
+-------------
+
+Like most web applications, dashboard binds to a host name and port.
+By default, the ``ceph-mgr`` daemon hosting the dashboard (i.e., the
+currently active manager) will bind to port 7000 and any available
+IPv4 or IPv6 address on the host.
+
+Since each ``ceph-mgr`` hosts its own instance of dashboard, it may
+also be necessary to configure them separately. The hostname and port
+can be changed via the configuration key facility::
 
   ceph config-key put mgr/dashboard/$name/server_addr $IP
   ceph config-key put mgr/dashboard/$name/server_port $PORT
 
-where ``$name`` is the ID of the ceph-mgr who is hosting this dashboard web app.
+where ``$name`` is the ID of the ceph-mgr who is hosting this
+dashboard web app.
 
-These settings can also be configured cluster-wide and not manager specific, eg:
+These settings can also be configured cluster-wide and not manager
+specific.  For example,::
 
   ceph config-key put mgr/dashboard/server_addr $IP
   ceph config-key put mgr/dashboard/server_port $PORT
 
 If the port is not configured, the web app will bind to port ``7000``.
-
-Setting the IP to ``::`` makes the dashboard bind to all available IPv4 and IPv6
-addresses.
-
-In addition, make sure that the *dashboard* module is enabled with::
-
-  ceph mgr module enable dashboard
-
-Please note that the dashboard will *only* start on the manager which is active
-at that moment. Query the Ceph cluster status to see which manager is active.
+If the address it not configured, the web app will bind to ``::``,
+which corresponds to all available IPv4 and IPv6 addresses.
+
+Load balancer
+-------------
+
+Please note that the dashboard will *only* start on the manager which
+is active at that moment. Query the Ceph cluster status to see which
+manager is active (e.g., ``ceph mgr dump``).  In order to make the
+dashboard available via a consistent URL regardless of which manager
+daemon is currently active, you may want to set up a load balancer
+front-end to direct traffic to whichever manager endpoint is
+available.