Nagios: dynamic check_load based on number of cpu/cores/threads, is there something like this

I've always believed the administration advantage of SSH (I use push_check) outweighs any additional load. Modern CPUs are so fast that the cost of encrypting a handful of bytes is pretty minimal, so it comes down to running two processes (SSH and the check script) vs one (check script fired off by NRPE).

For check scripts written in an interpreted language, I would expect the overhead of firing up the interpreter (Perl, Python, Bash) to exceed the CPU cost of starting an SSH session. Given modern CPUs, your machines are more likely to be disk or memory limited rather than CPU limited.

Provided your Nagios machine is coping -- it has to set up 20 SSH connections every second -- I would err on the side of convenience.

Not really an answer to your question, more of an argument that life is too short to worry about it :)

It then would run the check only against servers that are in both WWW-Servers and US-Servers, in my example, just www-us.

Is this feature available? If it isn't, will it be available in the future?

Ethan Galstad said that he doesn't have any plans to add intersection support.

Is there an alternative way to accomplish this given the most recent Nagios version?

You can exclude some hosts from the definition by preceding the host or hostgroup with a ! symbol. So, try something like this:

define service{
    use                     local-service
    hostgroup_name          *,!EU-Servers,!FTP-Servers
    servicegroups           WWW Checks
    service_description     Check HTTP Response Time
    check_command           check_http_response_time!50
}