Benefits of using active checks vs passive?

[tchjts1]

I have seen numerous mentions of using Zabbix agent (active) checks instead of passive checks. I have searched the forums but have not seen what the benefits of this are.

As of now, all of my hosts are using passive checks. Can someone explain the benefits (and any drawbacks) of using active checks?

Thanks.

Jeff

[nelsonab]

Active checks will reduce the load on your Zabbix server, here's how.

Passive check
1) Query items table for items which are due to be checked (MySQL query)
2) Connect with agent associated with item and retrieve data
3) Repeat 2 until list empty
4) Repeat 1 after a delay if needed

Active Check

1) Agent starts on host and queries server for items to be checked
2) Check list for items due to be sent to server. (List is in memory)
3) Repeat 2 until all items due to be sent have been sent to server
4) Query server after a timeout to see if there have been any changes to list of items
5) Repeat items 2-4 until termination

Ok so that's the basics, passive is heavily server based, active is heavily host based. Let's look a little closer. The item numbers relate to the steps above.

Passive
1) Query items table in SQL database for list of items to be queried (
2a) Connect to Agent
2b) Send item key
2c) Insert item into history table
2d) Update field in items table to show when the item was and should be checked next
3) repeat 2 until list is empty
4) repeat 2-3 (I believe there is a wait determined by the length of time until the next check, but I'm not sure)

Active
1) Agent starts
1a) Agent connects to server and requests items list
1b) Server queries database and returns list with item check frequency
2) Query list of items in memory to determine if any items need to be sent to server
2a) Connect to server and sent key and value
2b) Server inserts value into history table
2c) Server updates last check field in items table (Not sure about next check field however)
3) Repeat 2 until all items checked
4) After a timeout period (defined in zabbix_agentd.conf) Query server for list of items
4a) Agent connects to server and request list
4b) Server returns list of active items and check frequency
5) repeat 2-4 until termination

As you can see active checks are slightly more complex in their design. Active checks overall reduce the load on the server by distributing the effort to check items to the hosts. I need to dive a little deeper into the code sometime to answer some of my own questions from the above, but hopefully you get an overall idea of what's going on.

[tchjts1]

Thank you very much, Mr. Nelson. Excellent sequence.

[Alexei]

Use of active checks is strongly recommended for monitoring of large environments! This improves performance and also makes ZABBIX server immune to any sorts of network problems.

[w00tburger]

Better description in my post below.

[w00tburger]

I noticed while utilizing active checks that the overall metrics were not accurate. The performance graph below is when I was running a heavy install on the system. I noticed that just before the Zabbix agent checked in, the CPU usage would drop to roughly nothing, and then immediately spike back up to ~80 percent or so. During this timeframe, the agent had sent back that it was hardly under any load.

I activated passive checking, and you can immediately see the graph grow reflecting its true results. Re-niceing and prioritizing the zabbix agent on my linux system (while running active mode) had no affect on obtaining accurate results. Below I have labeled when I was running active vs running passive below. Has anyone had any similar experiences to this?

Zabbix agent marked topped system priority


Overall results: