Wednesday, 6 January 2016

Restoring Publisher Database From the Subscriber

I've been meaning to write about this feature for a while now, since it's actually pretty handy. Cisco introduced a feature whereby you can restore the publisher's database from a subscriber server in v8.6(1) of CUCM & CUC. You still have to rebuild a new publisher identical to the failed one, then get the licences migrated (if applicable) & the method differs between CUCM & CUC. Having seen several scenarios where customers have either only the original DRS backup done at go live or out of date backups available, this will help you get out of a sticky situation & back to a working cluster without losing any configuration data.
The Cisco documentation is pretty good for these features, so I'm going to cover some caveats & defer to the official instructions. Be aware that there are quite a few steps that must be followed correctly otherwise you run the risk of pushing data from the blank publisher to subscribers, it also includes multiple reboots, so this is a time consuming process.

The DRS restore mechanism has been enhanced so that you can choose to restore the CCMDB component from a selected subscriber server. Now the Cisco guide says you can do a fresh DRS backup from the newly built publisher & do the restore from a subscriber, but whenever I've tried the option never appears unless the actual backup contains files from the intended subscriber server. So you'll need a DRS backup that contains both the publisher & subscriber server.

The main caveat is that your new publisher won't have files that aren't in the backup or have changed since then, such as certificates, device packs, TFTP server files (e.g. phone loads, music on hold, etc.) or logs/traces. This is because this information isn't held in the Informix database, which is what gets copied from the subscriber, so you'll need to deal with these out manually.

Cisco Guide to CUCM Restore From Subscriber

CUC's clustering is different from CUCM, in that you still have a publisher & subscriber, but there's also the concept of the primary & secondary server. The primary server, regardless of whether it's the publisher or subscriber, contains a writeable configuration database & message store; normally this is automatically replicated to the secondary server.
After rebuilding the publisher you're basically rebuilding the cluster, with the subscriber as primary & manually starting the synchronisation process.

The main caveat is that the publisher needs locales & any other patches installing manually, as these aren't pulled across from the subscriber. The Informix database with configuration, message store, spoken names, greetings & master certificates are what gets copied from the subscriber. You'll still need to deal with certificates that were specific to the publisher server, such as the Tomcat certificate.

Cisco Guide to CUC Restore From Subscriber