Special agents

The Checkmk agent cannot be installed on some systems, and SNMP is not—​satisfactorily—​available. Nevertheless, Checkmk can still monitor such a system—​as long as there is an application programming interface (API) with which Checkmk can retrieve the monitoring data. Such an API is usually based on Telnet, SSH, HTTP/XML or HTTP/JSON.

The special agents generate agent output from the collected data. In some cases, the monitoring data is output in a format that can be evaluated by checks that process 'normal' monitoring data. In other cases, the monitoring data is output in separate agent sections, which in turn requires additional check plug-ins. Special agents are so named because they are a special replacement for the normal Checkmk agent.

You do not need to handle the calls to these APIs yourself, because Checkmk provides the necessary special agents and check plug-ins for commonly used systems.

Because special agents sometimes require quite complex parameters, we have defined special rule sets in the Setup GUI that allow you to configure them directly. You can find these rule sets grouped by use cases under Setup > Agents > VM, cloud, container and Setup > Agents > Other integrations:

As an example, let us take the monitoring of NetApp Filers. These do not allow the installation of Checkmk agents. The SNMP interface is slow, flawed and incomplete. There is however a special HTTP interface which provides access to the NetApp Ontap operating system and all of its monitoring data.

The agent_netapp_ontap special agent accesses this interface via a REST API and is set up using the NetApp via Ontap REST API rule set. The data required by the special agent can then be entered into the rule’s content. This is almost always some sort of access data. With the NetApp special agent there is also an additional option for selecting the resources to be collected:

It is important that you leave the host set to API integrations if configured, else Checkmk agent in the Setup GUI.

There are occasions in which it is desired that both a special agent, as well as the normal agent are to be queried. An example for this is the monitoring of VMware ESXi over the vCenter. This latter is installed on a (usually virtual) Windows machine, on which reasonably enough a Checkmk agent is also running: