[user5994461]

Indeed, I gave a list of all the tools, you only need to make a stack of about 4 to 8 of them to get the job done.

Let's say statsd + collectd (metrics collection) + graphite (aggregation) + carbon/whisper (graphite storage) + icinga (alerting) + grafana (graphing). That doesn't exactly come easy.

No offense but a single graphite is not a monitoring solution. It's just the tip of the iceberg. Monitoring does take a lot of engineering work and a lot of maintenance. You won't get away operating 600 hosts on the cheap, just think about how much are the hosts themselves.

[foobarian]

Let's talk about how much Amazon will charge you for 600 instances a year...