I use collectd and have found it to work rather well. The documentation could certainly use some work, but once you get figure things out it's pretty easy to co

I use collectd and have found it to work rather well. The documentation could certainly use some work, but once you get figure things out it's pretty easy to configure. CPU usage is almost non-existent for the amount of data monitored. It's also pretty easy to write a custom plugin to collect whatever custom metrics you want. I use a script to expose the current values out as http/json for integration with Circonus for monitoring/alerts of key values. You can use whatever graphing tools you'd like, things are stored in rrd format. Recently I've been implementing salt stack, and collectd is really easy to automate config of. I've got salt fully configuring collectd, and then using the circonus api to setup monitoring rules automatically per applied states. It's a beautiful thing.