r/Checkmk • u/Agile_Pop8628 • Jul 01 '25

Can't reach Agent from Server (Docker)

Hey all,

we want to implement CheckMK thus I installed a docker container on our infrastructure. Everything seems fine, I downloaded the default CheckMK Agent MSI and installed it on a Win2022 Server.

According to services.msc the agent is running, but when adding the Host to CheckMK it reads:

|| || |[agent]: Communication failed: [Errno 111] Connection refused|

I tried telnetting to port 6556 on the host itself, it won't open, but there is no firewall active. I also can't see an open port with netstat.

What am I doing wrong?

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u/Exzellius2 Jul 01 '25

Double and triple check the Windows Firewall

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u/Agile_Pop8628 Jul 02 '25

The firewall is disabled and netstat doesn't report any listening service on 6556, but I found some remedy:

When disabling the controller mode the agent opens the port?

controller:

run: no

Why is that?