Why the host shows up as unreachable on the zabbix server

zabbix

I have a zabbix server and an agent, on two different computers. The agent runs in active mode, e.g. I have this in the config file:

StartAgents=0
ServerActive=my.zabbix.server.com
Hostname=my.zabbix.agent.com

The zabbix server can be reached from the machine with the agent, e.g.:

telnet my.zabbix.server.com 10051
Trying 111.111.111.111...
Connected to my.zabbix.server.com.
Escape character is '^]'.
Connection closed by foreign host.

Moreover, the host auto registration was turned on on the server, and the agent has successfuly registered the host when I first started it. So the connection must be alive. This is what I see in the agent's log when I start it:

83074:20171128:082440.324 Starting Zabbix Agent [my.zabbix.agent.com]. Zabbix 3.4.1 (revision 71734).
83074:20171128:082440.324 **** Enabled features ****
83074:20171128:082440.324 IPv6 support:          YES
83074:20171128:082440.324 TLS support:           YES
83074:20171128:082440.324 **************************
83074:20171128:082440.324 using configuration file: /usr/local/etc/zabbix34/zabbix_agentd.conf
83074:20171128:082440.324 agent #0 started [main process]
83076:20171128:082440.325 agent #1 started [collector]
83077:20171128:082440.326 agent #2 started [active checks #1]

In other words, the agent could connect to the server, it even recognized its version. Nothing else happens in the agent log.

On the server, it still says that the host is unreachable!

What could be the problem?

UPDATE: on the front end, I see this message:

ZBX red error message

I'm not sure why it wants to connect to 10050? It is used for passive agents. My agent should be active.

UPDATE2: If I delete the host from the zabbix server, and restart the agent, then the following happens:

The host is auto-registered on the server again. The agent log:

14551:20171128:193954.483 Starting Zabbix Agent [my.zabbix.server.com]. Zabbix 3.4.1 (revision 71734).
14551:20171128:193954.484 **** Enabled features ****
14551:20171128:193954.484 IPv6 support:          YES
14551:20171128:193954.484 TLS support:           YES
14551:20171128:193954.484 **************************
14551:20171128:193954.484 using configuration file: /usr/local/etc/zabbix34/zabbix_agentd.conf
14551:20171128:193954.484 agent #0 started [main process]
14553:20171128:193954.485 agent #1 started [collector]
14554:20171128:193954.485 agent #2 started [active checks #1]
14554:20171128:193954.614 no active checks on server [my.zabbix.server.com:10051]: host [my.zabbix.agent.com] not found

where:

  • my.zabbix.server.com is the server's FQDN
  • my.zabbix.agent.com is the agent's FQDN, and also the HostName parameter in the agent's config.

So it seems, that the agent registers the host successfully, but for some reason, the server tries to get the information from the agent in passive mode. Despite the fact, that the agent was configured in active mode.

UPDATE 3: Although the agents are sending data, the host list still shows a problem:

enter image description here

Availability/ZBX has a red flag, and a message saying that "Get value from agent failed: cannot connect to [[ip_address_here]:1050]: [4] interrupted system call". I have checked every single item and every discovery for these hosts, and all of them have type="Zabbix Agent Active". So I don't understand why the server is trying to connect to them in passive mode??? This does not cause a real "problem" (e.g. something that generates an action and sends out notifications from the zabbix server), but it is very disturbing to see red flags on the screen.

Until this problem is fully solved, I won't even accept my own answer.

UPDATE 4: after changing all item types, discovery types, and the types of the item prototypes of the low level discovery rules of all templates that are connected to my hosts, and all of the templates linked form there, the ZBX red flags finally disappeared. I believe that I'm an experienced software user, but it was quite difficult to understand what is going on, and change all of the parameters to make it work.

Best Answer

For active checks to work, agent hostname must match the host hostname in the Zabbix server. "Agent hostname" is not the system hostname necessarily - it depends on the configuration parameters "Hostname" and "HostnameItem". Host hostname in Zabbix is not the DNS or the IP address - it's the contents of the "Host" field in the host properties.

When agent starts, it prints out the hostname it is sending to the server. In your example: Starting Zabbix Agent [my.zabbix.server.com] - that is, agent identifies itself to the server as my.zabbix.server.com. Make this value match the proper hostname (note that it is case sensitive) and active checks will start working. Note that the other host could have incorrect values if two or more agents were sending data, identifying as it.

Note that the version printed in the agent log is the agent version, not the server version - agent cannot determine server version.

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