Werk #12907: check_mk_agent: Fix issues with systemd

Component Checks & agents
Title check_mk_agent: Fix issues with systemd
Date Jul 26, 2021
Checkmk Editon Checkmk Raw (CRE)
Checkmk Version 2.1.0b1 2.0.0p10
Level Trivial Change
Class Bug Fix
Compatibility Compatible - no manual interaction needed

When deploying the checkmk agent on systemd based systems, users often encountered problems when hitting the limit of 3 connections per source (the monitoring server in this case).

In addition the real time checks would not work for the same reason.

This was due to systemd not terminating the connection until all child processes started by the agent had completed, including the started updates of the cached plugins, which were meant to be executed asynchronously.

This is solved by adding a second service to checkmks systemd units:

check-mk-agent@.service: The preexisting service. It is triggered by a remote connection of the monitoring server to the socket. This service no longer triggers the asynchronous jobs. It only outputs the available results.

check-mk-agent-async.service: The new service. It consists of an agent process kept running in the background. It checks every 60 seconds wether new asynchronous jobs need to be started, to update the caches for cached plugins, and (if configured) run the real time checks. The created monitoring data is stored on disk.

The (preexisting) agent process triggered by the socket will then output the prepared cached information.

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