I set up a Nagios server for monitoring the servers at work a while ago. It works just great. Highly recommended.
Then one of my colleagues wanted to look into whether we could monitor a Google Search Appliance (GSA) using the Nagios server. He found out that that can only be done using SNMP as you are not allowed to really get down to the OS of the GSA. He found it difficult to find his way through how to make it work. So I did a bid of research.
First I wanted to know if Nagios is able to monitor servers that expose SNMP-information. The answer looks to be a yes: check_snmp.
Then I wanted to get access to a server that was exposing SNMP-information. And for me the logical choice is to look at what Domino has to offer. And Domino does have an option for SNMP.
You need to install and configure something on the OS and then you need to install a Domino-specific service and load at least one Domino server task. The place to look for the Domino end of this is in the Administrator documentation, look for a document titled "The Domino SNMP Agent".
Then there is the Nagios end of things. How to get Nagios to get hold ot the SNMP information that Domino is making available. Here I found something that looks very interesting: Monitoring Lotus Notes/Domino Servers. It was posted a while back, but I would be surprised if it wouldn't work.
Be aware of the three downloads available from the bottom of the page. Especially the one labelled lotus-monitoring.tar.gz. Looks good. It's Domino-specific SNMP checks. For things like how many emails are dead or the availability index.
Finally I also found a promising script for Nagios - a Nagios plugin - that will probe SNMP information on the GSA: You can find information on this page: Monitoring a Google Search Appliance with Nagios. You have to scroll down a bit to find the section on Google Search Appliance monitoring.
I have not tested any of these things, but they look good. Well, actually I did test the GSA-specific script, and it told me our internal GSA wasn't responding... In all likelyhood the GSA hasn't been configured to expose SNMP data.