The Check_MK micro core (CMC)
Last updated: July 08. 2016
1. The monitoring core
The monitoring core is at the heart of the Check_MK-System. Its tasks are:
The diagram below shows the core and its connections to the primary elements of the
1.1. Nagios and Icinga
Alternatively, the core from Icinga can also be utilised. This is particularly popular in Germany, and is based on the same program code, but in recent years it has been developed independently.
Even though Nagios and Icinga perform exceptionally - being flexible, fast and well-proven - there are still situations in which their limits are reached. Where a large number of hosts and services are being monitored, three problems in particular become evident:
2. The Check_MK micro core
Since Check_MK is being used in ever-larger environments, and in order to overcome
the limitations of Nagios as described above, in 2013 we commenced a new development of
our own core specifically for the
Other elements have also been optimised. For example, performance data is passed without detours directly from the core to the RRD cache, notifications are created in a "KeepAlive"-mode, and host checks are executed by a built-in ICMP helper. All of these reduce costly process-creations and save CPU resources.
These characteristics bring numerous advantages - even in smaller installations:
The graphic below shows the CPU consumption for a Check_MK server before and after the installation of Nagios on the CMC. This graphic has been kindly provided by Munich Airport, which monitors 730 hosts and 18,000 services with this server.
Another project shows similar results. The following graphs show a restructuring of Nagios as the core on the CMC in an environment with 56,602 services on 2,230 monitored hosts on a virtual machine with two cores:
The magnitude of the difference in an individual case naturally depends on many factors. In the above case a smaller instance that was not restructured runs on the same server. Without this the difference in consumption would be even more noticeable.
Further articles on the CMC:
3. Frequently Asked Questions (FAQs)
3.1. Can the CMC also run normal Nagios Plug-ins?
3.2. Will Check_MK continue to support Nagios?
3.3. Can I switch between Nagios and CMC?
Switching between the two cores is simple, as long as your configuration has been created cleanly
with WATO. Details on this can be found in the Migration to the CMC article.
By default the
3.4. Is the CMC freely available?
The CMC is only available as a component of the