Simple application monitoring

I have just had a server halt itself and it took me some time to
notice. I am planning on implementing some application monitoring
using an external service that polls the website from outside. If it
can't reach it then it will SMS me or something. (I would like Prowl
on my iPhone and Mac at the same time).

I could point the monitoring service at one of the application URLs
but I wondered whether anyone had come up with a better idea along the
lines of creating some external monitoring URL, performing a GET and
then returning some additional information in the XML response, such
as response time, SQL execution time, number of users logged on,
memory usage etc etc.

Any thoughts? Is there a plugin or gem about?

O.

Well if you are using a unix based system then I would recommend monit ( http://mmonit.com/monit/ ). We use it watch the web server, database, memcached and a whole heap of services and restart them if they go down. It will also send you an email when things go down or come back up.

I know this is not a ruby / rails thing but it is a good tool for monitoring services.

Or you could try God. http://god.rubyforge.org/

A ruby-based monitoring system like Monit.

Yeah, we looked at that.

Monit is simple and it works, God was neither IMHO.