Zabbix Proxy cannot send Proxy data to Zabbix Server (empty string received)

[jan.1337]

Hi guys,

I have the problem that my Zabbix proxy doesn't send data to my server reliable. The problem is occuring since a short time. Before that error everything worked flawlessly. I keep getting following errors in the proxy log:

4541:20231229:085433.424 cannot send proxy data to server at "SERVERIP": empty string received
4541:20231229:090435.537 cannot send proxy data to server at "SERVERIP": gnutls_record_send() timed out

I already checked the networking between the proxy and my zabbix server. All traffic is routed through a Site-To-Site Tunnel. I also tried raising the log level. The higher log level on the proxy sadly doesn't give more information. All gnutls log records are correct and it says TLS connection established. It also says that the data is put successfully to the zabbix server. All the time it stops working the proxy log simply doesn't show anything about the connection to the server.
The weird thing is that it works initially when I start the proxy. After waiting for about 7-15minutes it just stops to work. When I wait some more time it sometimes starts to work again for a short period of time.

The proxy monitors about eight windows vms with the zabbix agent and one firewall by snmp.
There are also about ten other proxies from different sites talking correctly to my zabbix server.

Proxy Version: 5.0.26 (after reinstall 5.0.40)
Server Version: 5.0.38
Agent Version: 5.0.26 (after binary swap 5.0.40)

Things I tried:
- Checked the networking between proxy and server (VPN tunnel, firewall policies, TCP dump, telnet, traceroute...)

- Reinstalled the proxy on a fresh Ubuntu Server 22.04 VM (vSphere VM)
- Raised the log level of the proxy and analyzed it
- Checked the zabbix server log
- Checked if server, proxy and agent versions are compatible
- Disabled TLS connection and tried sending the data unencrypted to the server (tls error stops showing up, empty string received still shows up)
- Deleted all hosts on the zabbix server
- Disabled every host except the firewall which is monitored by snmp
- Rolled out new Agent binaries on the monitored VMs


Would appreciate any troubleshooting idea

Greetings
Jan

[jsrozo]

Hi,

Can you solution this problem?

I have the same error:

cannot send proxy data to server at "X.X:X.X": empty string received

[jan.1337]

Sadly we weren't able to find out what the problem is. It just stopped happening one day without us touching anything. Unfortunately it started again after some time. The last guess we had is that there are some kind of network issues in the network of the customer that makes the connection drop (Layer 1 or 2). We didn't proceed to troubleshoot the problem further.

[adev2]

Hi,

I was having the same issue. I am gonna share my solution.

So, I was having on my zabbix server:

> cannot parse proxy data from active proxy at XXX": missing name of proxy

The solution was:
1: Remove from the GUI all my proxies.
2: Restart the proxy service + maybe the zabbix server until I got not more error in my logs.
3: Add the proxy again, and I saw in the log of the proxy

> 162551:20250116:161518.749 received configuration data from server at "XX", datalen 1157257
> 162567:20250116:161521.769 enabling Zabbix agent checks on host "XX": interface became available

It would be nice if the development team could fix this issue as it was a pain to troubleshoot.