How to raise alert if a tcp port is responding in Icinga2

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I'm new to Icinga2. I have set up a couple of service checks. Now I want to check if a TCP port is responding, and if it does raise a down event. Basically I want to reverse the status, because normally this port should not be listening. How can I do that?

Best Answer

I found the solution. There is a plugin called "negate" that does exactly this. That's how you configure it:

object Host "hostname" {
        address  = "192.168.1.11"
        vars.negate_command = "/usr/lib/nagios/plugins/check_tcp"
        vars.negate_arguments["-p"] = "443"
        vars.negate_arguments["-t"] = "3"
        check_command = "negate"
}

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How to check if a service (that listens on given port) is up & working

Keeping to the standard Nagios plugins found on, say, an Ubuntu repository, you can use the check_tcp plugin to send a string, and then check to see if it returns the expected response:

Usage:check_tcp -H host -p port [-w <warning time>] [-c <critical time>] [-s <send string>]
[-e <expect string>] [-q <quit string>][-m <maximum bytes>] [-d <delay>]
[-t <timeout seconds>] [-r <refuse state>] [-M <mismatch state>] [-v] [-4|-6] [-j]
[-D <days to cert expiry>] [-S <use SSL>] [-E]

Since you can modify your service, you can do something like "Are you OK?" and look for "I'm OK". It depends on how involved you want to get with checking to see if the service is up and running.

You can also use check_procs to see if the process for the service is there. This might be in conjunction with a check_tcp check, or as an alternative. Again, it depends on what you're doing, and how much you actually want to do. If you want to get very involved, you can write a custom Nagios check that will do all sorts of things to verify the functionality of the service and return custom state messages to the Nagios server.

How to divide hosts by groups in Icinga2 properly

I wouldn't depend on hostgroups for that - they can be used to group hosts for external user interfaces and help as a basis, but I would recomment looking into alternate apply rule match conditions such as

custom attributes as strings, numbers, boolean, arrays or (nested) dictionaries
name pattern match with wildcards/regex
match on object attributes, such as ip address subnets

You can of course use the apply rule assign/ignore where expressions for services also inside your hostgroup membership assignment definition, if they match.

Another cool thing you can do with Icinga 2 - use apply for rules and grnerate services based on host custom attributes as array or dictionary. That way you'll pass the entire check information from the host to the service apply rules if you want to.

Look at the docs for a detailed explaination and example: http://docs.icinga.org/icinga2/latest/doc/module/icinga2/chapter/monitoring-basics#using-apply-for

Best Answer

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How to check if a service (that listens on given port) is up & working

How to divide hosts by groups in Icinga2 properly

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