I need a monitoring system, much like ganglia / nagios that is build for the cloud.

I need it to support :

• Adding / removing nodes dynamically. (Node shuts down, dose not imply node failure...)
• Dynamic node based categorization, meaning node can identify them self as being part of group X (ganglia gets this almost right, but lacks the dynamic part...)
• Does not require multicast support (generally not allowed in cloud based setups)
• Plugins for recent cool stuff such as Hadoop, Cassandra, Mongo would be cool.

More features include: External API, web interface and co.

I've looked at Ganglia, munin and they both seem be almost there (but not exactly). I would also go for reasonably priced Software as Service solution.

I'm currently doing research, so Suggestions are highly appreciated.

Thank you,
Maxim