Zabbix server and proxy 3.0.2
OS: Debian 8

How much time passes between "sending ..." and "cannot send ..." messages?

Do you use TLS between Zabbix server and these proxies? If so, which encryption libraries do you use?

Thanks for your reply.

3 seconds between sending and timeout:
2493:20160502:113436.526 sending configuration data to proxy "CZ_Zabbix_proxy_01" at "172.22.2.251", datalen 1859411
2493:20160502:113439.526 cannot send configuration data to proxy "CZ_Zabbix_proxy_01" at "172.22.2.251": ZBX_TCP_WRITE() timed out

No, we are not using TLS, all TLS settings are on default (unencrypted)

There seems to be a difference between how Zabbix server handles passive and active proxies. With passive proxies (as can be seen in src/zabbix_server/proxypoller/proxypoller.c), it uses a timeout of CONFIG_TRAPPER_TIMEOUT (300 seconds) to send configuration data. With active proxies (as can be seen in src/zabbix_server/trapper/proxyconfig.c), it only uses a timeout of CONFIG_TIMEOUT (3 seconds by default). However, this issue seems to have existed forever, so it is currently unclear why you are experiencing this problem after upgrade to 3.0.

OK, but why does the proxy expecting larger data package and drops the received one?

One reasonable guess would be that, since ZBX_TCP_WRITE() times out, Zabbix server fails to send all data (it sends the length of the data in the message header). Therefore, proxy drops whatever it has received, because the data is incomplete.

How can I increase the value of CONFIG_TIMEOUT ?

Just increase Timeout parameter in your configuration file.

Thanks a lot. Transmitting the data package lasted 8 seconds.
I changed the value to 10 sec.

Now it is OK.

Fixed in development branch svn://svn.zabbix.com/branches/dev/ZBX-10727 by replacing CONFIG_TIMEOUT with CONFIG_TRAPPER_TIMEOUT in send_proxyconfig() function.

Successfully tested

Fixed in pre-2.0.18rc1 r59893, pre-2.2.13rc1 r59894, pre-3.0.3rc1 r59896, pre-3.1.0 (trunk) r59897.

The reason why it started to fail with such message after upgrade to 3.0 is ZBX-8914 which improved/introduced validation of received message length against what was promised in the header. Although incomplete data would cause error anyway, "invalid JSON..." or something like that.

this issue it seems to be back on debian 8 with zabbix

9342:20170629:140129.903 sending configuration data to proxy "ProxyIP" at "172.30.7.98", datalen 461682
9342:20170629:140629.903 cannot send configuration data to proxy "ProxyIP" at "172.30.7.98": ZBX_TCP_WRITE() timed out

zabbix_server (Zabbix) 3.2.6
Revision 67849 4 May 2017, compilation time: May 6 2017 15:48:59

zabbix_proxy (Zabbix) 3.2.6
Revision 67849 4 May 2017, compilation time: May 6 2017 15:59:40

Linux ipproxy 3.16.0-4-amd64 #1 SMP Debian 3.16.43-2 (2017-04-30) x86_64 GNU/Linux

Well, I see no indication of a bug. Server was trying to send data to proxy for 5 minutes, but timed out. Proxy received incomplete message (length stated in header is larger than what proxy managed to read from socket) and ignored this message (letting you know what happened).