Merge pull request #341 from arista-eosplus/ztr-doc

Add more ZTR information to docs

docs/cookbook/advanced.rst

@@ -6,8 +6,8 @@ Advanced
 .. contents:: :local:
   :depth: 1
 
-Configuration Management and ZTR
---------------------------------
+Configuration Management and prep for ZTR
+-----------------------------------------
 
 Objective
 ^^^^^^^^^
@@ -80,10 +80,31 @@ Copy and paste the option text into a new template in:
    ! For serial number, non-default VRF:
    action bash export SERIAL=`FastCli -p 15 -c 'show ver' | grep Serial | tr -s ' ' | cut -d ' ' -f 3 | tr -d '\r'`; sudo ip netns exec ns-$vrf_name curl http://$ztpserver:$port/nodes/$SERIAL/startup-config -H "content-type: text/plain" --data-binary @/mnt/flash/startup-config -X PUT
 
+Zero-touch replatement (ZTR)
+----------------------------
 
-Explanation
-^^^^^^^^^^^
+Objective
+^^^^^^^^^
+
+I replaced a switch with a new one and want it to provision with the same
+configuration and, optionally, EOS version as the node it replaced.
+
+Solution
+^^^^^^^^
+
+ZTPServer first looks for a pre-existing definition for a node in the
+``<configdir>/nodes/<node-id>`` directory before trying to match through neighbordb, etc.
+Thus, you can make ZTPServer think it has already seen this node by
+renaming, linking or copying the old-node's directory to the new-node's
+unique-id before powering the switch on for the first time.
+
+Moving (renaming) or linking are most commonly used, however, making a
+recursive copy will ensure that the last-known configuration of the previous
+node remains stored as a backup.
+
+.. code-block:: console
 
-(add explanation here)
+  cd /usr/share/ztpserver/nodes
+  ln -s <old-node_id> <new-node_id>
 
-.. End of <RECIPE TITLE>
+.. End of ZTR