Couchbase StateManager for XPages, Part 2

Feb 21, 2014 10:17 AM

  1. Couchbase StateManager for XPages, Part 1
  2. Couchbase StateManager for XPages, Part 2

I had the opportunity to dive a little back into the StateManager I wrote the other week to try out a theory. The first thing I noticed was that there was a minor problem: it didn't work at all. Specifically, the code I had didn't actually store the whole proper state of the view, so it ended up being regenerated anew each time; the fact that this didn't cause an error was what led me astry.

Fortunately, I was able to scrounge together enough code to get it to work properly, bringing the tree and viewScope along for the ride:

CouchbaseStateManager.java

The impetus of revisiting this was to test whether this setup would be enough to accomplish a fun goal: by having the view state serialized to a commonly-available location, you should be able to switch servers in between actions (e.g. partial refreshes) and still have it work. And indeed, it does! I set up a round-robin load balancer for two of my Domino servers, which more or less switches between Arcturus and Ceres on each hit. In my test page, you can see a refresh count (stored as an instance member of the page's controller class, which is in viewScope) incrementing when you click the button:

https://roundrobin.frostillic.us/tests/ccluster.nsf

You can also see a value stored in "clusterScope", which is an object pointing to the same Couchbase cluster, and so it is similarly available on both servers.

This is pretty promising! It's not the sort of thing you'd do with any old app (importantly, applicationScope and sessionScope are not shared between the servers), but by pairing this with SSO, you could make an app that is resilient and scalable, with an arbitrary number of app servers behind a rotating load balancer without the need of sticky sessions.

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