For alerts i am using nagios as it has all kind of checks for most services integrated. Besides services i also monitor security updates (any security upgrades available which are not installed) for debian hosts and resource shortage of openvz containers.

I am also using monit for immediate actions like restarting web server or checking some programs.

I manage both via puppet, that means I deploy a new host and the nagios configuration gets adjusted automatically with the corresponding services.

For performance data there are several tools like cacti, munin or collectd.

- Munin has iirc the problem thats it gets slowish as it polls all data from hosts then generate the carts for all hosts. Only a problem if you have many hosts...

- Collectd is a quite nice and fast monitoring solution (supports updates every second) and has advanced features like sending the data to multicast addresses. The only imho major drawback is that there comes no good webui bundled with collectd though many external uis exists.

EDIT: I forgot to mention icigna http://www.icinga.org/ a fork of nagios after some trademark problems iirc.

Monit and nagios are integrated with the ticketing system, e.g. recovery message closes automatically the corresponding ticket.