Configure active zabbix agent

I think that the bottleneck is the disc. Here are my reasons for this:

You have a pretty busy web server. Zabbix is slow, I suspect to be reads from the disk (can be from the network too).

Run again the strace, and find the file descriptor in Zabbix

Then find if the file descriptor is a file or a socket:

ls -l /prod/<PID_of_straced_process>/fd/<FD_from_strace>

EDIT1:
You should not change the TIME_WAIT timeouts. The problem with small HTTP keep-alive, or with no HTTP keep-alive is that you increase the latency and bandwidth. Instead you should increase a little bit the HTTP keep-alive and install/enable SPDY.

EDIT2: Use dstat -ta 10 and compare the first line with the rest. The first line is the average since boot. Next lines are 10 seconds average (the last parameter).

EDIT3: Check if you do not have packets lost, use something like smokeping to monitor the server and the website from outside your network. You have a significant number of connections in CLOSING, FIN_WAIT1, FIN_WAIT2, SYN_RECV, LAST_ACK. I think your network is congested or you have a lot of short lived connections (confirmed by the high TIME_WAIT/ESTABILISHED ratio). See: http://en.wikipedia.org/wiki/Transmission_Control_Protocol#Protocol_operation

I found the answer eventually.

It seems creating a full clone of the template Template App Zabbix Agent to a new Template Template App Zabbix Agent Active.

Then in the 3 items linked to this new cloned template

• Agent ping
• Host name of zabbix_agentd running
• Version of zabbix_agent(d) running"

Change the type field for each item from Zabbix agent to Zabbix agent (active) and save each one.

I then created another cloned template Template OS Linux Active and changed the linked template to the new one Template App Zabbix Agent Active.

Now when this new template Template OS Linux Active is linked to my hosts they correctly gather data without complaint about not being able to connect to the zabbix agent.