False unreachable alerts with proxy (suddenly)

[stratos]

Hello,

I have a very simple setup with a zabbix server and one active proxy (both version 2.4.8). Out of the sudden I started to get false unreachable alerts for all hosts monitored through the proxy. In the beginning I was suspecting a network issue between the server and the proxy but after running several tests, network is stable and working without loss or any other issue.

This happens randomly but very often. I'm getting host unreachable for all the hosts managed by the proxy. I tried to revert the proxy to passive mode with the same result.

The only thing I can spot in the logs when the issue is appearing is this:

1715:20160509:125910.134 sending data to server failed: error:"invalid response format: empty string received", info:""

on the zabbix_proxy.log

No change has happened on the configuration and there is no resources issue, both server and proxy are fine and the host number is very small (around 50 hosts).

If anyone can point me on how to debug this more or has any idea, I would be grateful to hear it. The setup was working fine for long time and I don't exactly remember if the issue has started after upgrading to 2.4.8 from 2.4.7 but it is constant for the last 4-5 days. Alerts are silenced immediately and all are false.

Thanks in advance.

[stratos]

The error in the proxy log is for sure about the issue. I was monitoring the behavior for some time and every time this line appears on the logs I have "Unreachable alert" for all hosts managed by the proxy, which is silenced immediately.

  8349:20160509:141945.410 proxy #82 started [discoverer #1]
  8225:20160509:141945.867 received configuration data from server, datalen 219112
  8225:20160509:143446.628 received configuration data from server, datalen 219112
  8227:20160509:143927.172 sending data to server failed: error:"invalid response format: empty string received", info:""
  8347:20160509:144945.529 executing housekeeper
  8347:20160509:144945.892 housekeeper [deleted 68691 records in 0.362276 sec, idle 3600 sec]
  8225:20160509:144947.387 received configuration data from server, datalen 219112
  8225:20160509:150448.149 received configuration data from server, datalen 219112
  8225:20160509:151948.913 received configuration data from server, datalen 219112
  8227:20160509:153112.584 sending data to server failed: error:"invalid response format: empty string received", info:""
  8225:20160509:153449.679 received configuration data from server, datalen 219112
  8347:20160509:154946.141 executing housekeeper
  8347:20160509:154946.471 housekeeper [deleted 68109 records in 0.329441 sec, idle 3600 sec]
  8225:20160509:154950.436 received configuration data from server, datalen 219112
  8225:20160509:160451.195 received configuration data from server, datalen 219112
  8227:20160509:160812.362 sending data to server failed: error:"invalid response format: empty string received", info:""

I strongly suspect that this behavior was introduced with the 2.4.8 update.