Blackbox tcp_connect module blocks new client connections

[Vivek]

Hi All,

I want to monitor a socket program with Blackbox exporter's tcp_connect module. 

I have observed that if the exporter connects first to the socket program it can probe successfully as expected, but it also blocks any new connection requests to the socket program which defeats the actual purpose of socket program. 

However, if a third party client makes the first connection to the socket program instead of Blackbox probe then the above behavior is not observed.

Am I missing something?

My goal is to just monitor whether TCP port is UP or DOWN by using Blackbox exporter without affecting the actual functionality of the socket program which is to listen for incoming client connections.

Prometheus => prometheus-2.32.1.windows-amd64

Blackbox Exporter => blackbox_exporter-0.19.0.windows-amd64

Please advise.

Thanks in advance.

[Brian Candler]

There's something broken with your target if it cannot accept connections from two clients simultaneously.  It is a trivial denial-of-service if one user opening a TCP connection to the server blocks all other users.

This isn't a problem with prometheus or blackbox_exporter; you need to debug the target application.