False server not running, chrome only, one system only

[Linwood]

I upgraded three systems over this weekend, all from Ubuntu 16.04, Zabbix 3.4.x to Ubuntu 18.04.01 and Zabbix 3.4.12. All are running fine.

Only one of them is giving a "Zabbix server is not running" on the web.

But only in Chrome. And only that server.

The server is actually running. Edge and Firefox and IE work fine (current versions on W10x64). Data is updating. Seriously, the service is running, I'm sure.

I have this problem on two different PC's, both running Windows 10. I have no other issues with Chrome on either (at least on one, on the other is an adblocker and an ipv6 display, but again, on one there's literally nothing installed and all native ones disabled).

Only windows defender is running, no AV or similar programs. Connection to this server is fast (150/20 service, latency 48ms +/-5 steadily).

Did I mention it's only chrome?

On one I purged all history and cookies, etc., and it fixed it. For a while. Then it started failing again a day or so later. The service is running. Firefox and Edge and IE don't give the error.

I've tried changing the timeout in jsrpc.php to double the timeout (assuming this does it properly?):

$zabbixServer = new CZabbixServer($ZBX_SERVER, $ZBX_SERVER_PORT, 2 * ZBX_SOCKET_TIMEOUT, 0);

No change.

I don't know enough about the api (or ajax for that matter) to effectively debug this, All searches lead to discussions that seem related to either the service actually not running, or selinux (which I do not have).

Any ideas? Any ideas how to troubleshoot? It's very reproducible.

Thanks,

Linwood

[DmitryL]

The message appears when frontend is not able to connect to Zabbix server listening port (trapper process)
User browser only visualizes it. If a problem appears only in one browser on one workstation, I would start by updating/downgrading Chrome on that machine.

[Linwood]

DmitryL, I get that, but it's two client computers that give the message, both running the latest version of Chrome, and latest Windows updates.

The only common denominator is this specific server, and it only happened after the upgrade (whether it was the Ubuntu upgrade from 16.04 to 18.04 or the Zabbix upgrade from 3.4.4 to 3.4.12 I do not know.

I can open three browser tabs on the same Chrome instance, on three different Zabbix servers, and only the one server gives the error.

I suspect it's some cookie or session variable that's getting hosed, because if I clear all such data from Chrome, it works fine -- for a while. In a day or so it starts up again, but only on that one server (but on two different Chrome PC's). And no other browser (tried edge, IE and firefox) has issues for the same PC, same connection (VPN) and same server.

Is there a status readily available in that jsrpc.php routine I could display in the message that may say WHY it failed, e.g. timeout, connection refused, etc. that might give an additional clue?

But the only thing in common to all the failures are that specific server, or some aspect of my connection to it (I come in over a VPN). Though that is a good thing to explore -- I'll set up a local Chrome instance somewhere, and try it locally (they do not use Chrome normally at this client site, but I can find somewhere, or even spin up my own VM if nothing else, there).