config-sync: adding initial user documentation

(cherry picked from commit 07ae4323b3731061854e386bd53af5749862f031)

docs/configuration/service/config-sync.rst

@@ -0,0 +1,114 @@
+.. _config-sync:
+
+###########
+Config Sync
+###########
+
+Configuration synchronization (config sync) is a feature of VyOS that 
+permits synchronization of the configuration of one VyOS router to 
+another in a network. 
+
+The main benefit to configuration synchronization is that it eliminates having  
+to manually replicate configuration changes made on the primary router to the  
+secondary (replica) router.
+
+The writing of the configuration to the secondary router is performed through 
+the VyOS HTTP API. The user can specify which portion(s) of the configuration will 
+be synchronized and the mode to use - whether to replace or add. 
+
+To prevent issues with divergent configurations between the pair of routers, 
+synchronization is strictly unidirectional from primary to replica. Both 
+routers should be online and run the same version of VyOS.
+
+Configuration
+-------------
+
+.. cfgcmd:: set service config-sync secondary 
+   <address|key|timeout|port>
+
+   Specify the address, API key, timeout and port of the secondary router. 
+   You need to enable and configure the HTTP API service on the secondary 
+   router for config sync to operate.
+   
+.. cfgcmd:: set service config-sync section <section>
+
+   Specify the section of the configuration to synchronize. If more than one 
+   section is to be synchronized, repeat the command to add additional 
+   sections as required.
+
+.. cfgcmd:: set service config-sync mode <load|set>
+
+   Two options are available for `mode`: either `load` and replace or `set`
+   the configuration section.
+
+.. code-block:: none
+
+    Supported options for <section> include:
+        firewall
+        interfaces <interface>
+        nat
+        nat66
+        pki
+        policy
+        protocols <protocol>
+        qos <interface|policy>
+        service <service>
+        system <conntrack| 
+        flow-accounting|option|sflow|static-host-mapping|sysctl|time-zone>
+        vpn
+        vrf
+
+Example
+-------
+* Synchronize the time-zone and OSPF configuration from Router A to Router B
+* The address of Router B is 10.0.20.112 and the port used is 8443
+
+Configure the HTTP API service on Router B
+
+.. code-block:: none
+
+    set service https listen-address '10.0.20.112'
+    set service https port '8443'
+    set service https api keys id KID key 'foo'
+
+Configure the config-sync service on Router A
+
+.. code-block:: none
+
+    set service config-sync mode 'load'
+    set service config-sync secondary address '10.0.20.112'
+    set service config-sync secondary port '8443'
+    set service config-sync secondary key 'foo'
+    set service config-sync section protocols 'ospf'
+    set service config-sync section system 'time-zone'
+
+Make config-sync relevant changes to Router A's configuration
+
+.. code-block:: none
+
+   vyos@vyos-A# set system time-zone 'America/Los_Angeles'
+   vyos@vyos-A# commit
+   INFO:vyos_config_sync:Config synchronization: Mode=load, 
+   Secondary=10.0.20.112
+   vyos@vyos-A# save
+
+   vyos@vyos-A# set protocols ospf area 0 network '10.0.48.0/30'
+   vyos@vyos-A# commit
+   INFO:vyos_config_sync:Config synchronization: Mode=load, 
+   Secondary=10.0.20.112
+   yos@vyos-A# save
+
+Verify configuration changes have been replicated to Router B
+
+.. code-block:: none
+
+   vyos@vyos-B:~$ show configuration commands | match time-zone
+   set system time-zone 'America/Los_Angeles'
+
+   vyos@vyos-B:~$ show configuration commands | match ospf
+   set protocols ospf area 0 network '10.0.48.0/30'
+
+Known issues
+------------
+Configuration resynchronization. With the current implementation of `service 
+config-sync`, the secondary node must be online.

docs/configuration/service/index.rst

@@ -8,6 +8,7 @@ Service
    :includehidden:
 
    broadcast-relay
+   config-sync
    conntrack-sync
    console-server
    dhcp-relay