How does Check_MK work with Nagios? - nagios

Question

Hi I have just installed a clean copy of Nagios and Check_MK. But I don't understand how they work together. Nagios uses nrpe to connect to clients and performs checks. This means that some Nagios plugins have to sit on the client and return results from when they are called. But how does Check_MK tie into Nagios. Does it use check_mk_agent to replace all the Nagios plugins to perform its checks? Also does the Nagios configurations all have to be fully configured with all the clients already in place to be checked and then ported to Check_MK interface (wato) or can the clients be added to Check_MK without being present in the Nagios configurations. This is where my confusion lies and I cant find a concrete answer to this question anywhere. Please help.

Answer 1

Check_MK uses Nagios core for theses tasks:
Manage Check results
Triggering of alarms
Manage planned downtimes
Test host availability
Detect network failures
As you can see at the bottom of this page: http://mathias-kettner.com/checkmk_monitoring_system.html
Check_MK needs both: client side monitoring agent and server side monitoring system.
The server side monitoring system calls the agent of the host and passes the check results to the monitoring core (usually Nagios but there is also an new core just for Check_MK).
What makes Check_MK different from other passive Checks (like NRPE) is that the results for all checks is send to the monitoring system in one package. If you run the agent on a host in a shell it will return something like this:
➜ ~ check_mk_agent
<<<df>>>
/dev/mapper/MyStorage-rootvol ext4 15350768 13206900 1341052 91% /
dev devtmpfs 4022348 0 4022348 0% /dev
plus many more lines ....
So the server side part of Check_MK splits these packages into single checks so that the Nagios core can handle them.
So Check_MK wont replace your existing checks, it doesn't care about them. It will just add more.
You don't necessary need WATO to configure Check_MK. WATO is just an interface for the configuration. Configuration can also be done with plain text files. You should start with WATO and take a look at the configuration it has generated.