Agent2 MQTT Plugin issue - time out while subscribing

[Timo Hein]

Hello everyone,

I have a problem with the Agent2 and the MQTT plugin.
I have 14 hosts and about 1500 items to read so far. (later there will be more)
All via one Agent2, as the hosts are industrial controllers.
If the number of items exceeds approx. 1000 (sometimes even less), I get the following error message “time out while subscribing” for almost all items.



The setting “Timeouts for items types” seems to have no influence on the MQTT plugin.
Does anyone have an idea if there is a setting to increase the timeout or if there is a way to find out why it takes so long to subscribe?

Greetings Timo

[t00m1G]

Hey,

Everything about Agent2 you need to set in zabbix_agent2.conf file - in there you have section "PluginTimeout", but at first it would be better to check out agent2 logs. Logs might also help you with this: "if there is a way to find out why it takes so long to subscribe?"

Could you please provide logs for agent2? and if it's possible change DebugLevel in config to level 4 (config file name is: zabbix_agent2.conf), and then provide logs - you can read more about that here: https://www.zabbix.com/documentation...nt2#debuglevel
version for Agent2 (windows) if needed:

https://www.zabbix.com/documentation/current/en/manual/appendix/config/zabbix_agent2_win

[Timo Hein]

Hello,

Thank you for your reply.
I have already set this option “PluginTimeout” to the maximum of 30 seconds. I have also set the “Timeout” option to the maximum. Neither had any effect.
I have also checked the log file of Agent2 and the Zabbix service and raised the debug level. Unfortunately, I only found the same message there “timeout while subscribing”, but no reason for this.
As a “solution” I have now distributed the hosts to several Agent2s running in LXC containers. Now there are no more timeouts.
I don't think this is a good solution, because you don't know how many items lead to a timeout.

[t00m1G]

hey,
if there is possibility to do that, I would recommend to use tool like tcpdump to create .pcap file to further analyse of that issue, later you can use Wireshark to analyse that file, to see what's happening. But, I think that might be problem with big amount of items - there might be a need to see how your whole Zabbix instance is built.
there is also old discussion about similar issue, maybe it would also help you, here is link: https://www.zabbix.com/forum/zabbix-...-timeout/page2

[Timo Hein]

Thanks for your answer t00m1G.

I'll have to see how I do it with tcpdump.
I had a look at the post from your link.
This is about the agent in version 6.4.12 and 6.4.16.
I have Zabbix in version 7.0.2 and Agent2 in version 7.0.2.
The number of items (metrics) is much higher than described in the post and the connection is not unstable, but is not even established when the system is (re)started.

[Timo Hein]

Hello,
After some additional tests, I found out, that the problem is not the number of the items per host. It's the number of hosts.
The error occurs if the number of hosts, which is configured in the agent2 configuration file, is greater than (in my case) eight.
This means, if the MQTT-plugin of the agent2 needs to subscribe more than eight topics it takes longer than a timeout X which I cannot influence.
The strangest thing is that not all subscriptions fail, some of the subscriptions still work.
Any suggestions?

[Timo Hein]

Hello,
I have carried out a clean installation on another system.
I found out that with version 7.0.3 of the agent the problem gets worse.
I have configured the agent with 4 hosts, 1 host is the agent itself, 3 hosts work with mqtt and have 42 subscribed items.

Here is a short excerpt from the log file:

2024/09/13 07:38:17.805204 [MQTT] connection lost to [tcp://10.83.134.212:1883]: pingresp not received, disconnecting
2024/09/13 07:38:17.805973 [MQTT] connected to [tcp://10.83.134.212:1883]

2024/09/13 07:39:17.807394 [MQTT] cannot subscribe topic 'VSW02/#' to [tcp://10.83.134.212:1883]: timed out while subscribing
2024/09/13 07:39:17.807462 [MQTT] connection lost to [tcp://10.83.134.212:1883]: pingresp not received, disconnecting
2024/09/13 07:39:17.808604 [MQTT] connected to [tcp://10.83.134.212:1883]

I also tried to install version 7.0.1 of the agent and get the following message:

apt install zabbix-agent2=7.0.1-1
Package zabbix-agent2 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Version '7.0.1-1' for 'zabbix-agent2' was not found

Does anyone have any ideas what else I can do? zz0.g66as0u4umqzz

[klandos]

As written here:

https://www.zabbix.com/forum/zabbix-help/456267-mqtt-plugin-in-zabbix-agent-2-subscribe-was-broken-by-timeout/page2

Version 6.2.9 seems to be working without problems.

[roteki]

i have found this file /etc/zabbix/zabbix_agent2.d/plugins.d/mqtt.conf in which i have configured the options, then idk how to continue the configuration, I have read https://www.zabbix.com/fr/integrations/mqtt#mqtt but I couldn't understand quite well what must I do next
if you can tell me please in details how to configure the plugin
I'm using zabbix 7.0.5 btw

[Timo Hein]

Hi, this is just the basic configuration for the plugin. You have to add a host and items to receive data.
Please have a look here:
https://medium.com/@flaviofranca/usi...r-6df748b8f93e
or here:
https://blog.zabbix.com/let-me-subsc...-topics/12710/

Regards