Optimal timeout and interval settings for Apache health monitor

I don't think there's anything better than lowering those values at the moment. interval of 5 seconds and timeout of 16 seconds is the default for most monitors I think, and assuming your servers can serve up responses fast enough, and you don't have too many (many thousands) of monitors, you can probably get away with interval=2, timeout=7. Keep in mind that if you set the values too low, the F5 may be able to process them in a timely manner, but you will suffer unexpected timeouts if for any reason the actual server itself was too busy to respond within the timeout.

Basically, it's a double-edged sword. If you lower it, you get faster failure detection at the risk of increasing the fraction of false-negatives.

Thanks for the feedback. We were thinking something similar, where the F5 could identify a webserver being down within 5 seconds. Our current F5 administrator is stating that the default values are the recommended configuration.

Is there some kind of guideline/whitepaper on how to define health monitors?

Appreciate any additional information you can provide.

Regards,

Some enterprising people have cooked up solutions based on this irule event https://devcentral.f5.com/wiki/iRules.lb_failed.ashx

I won't be able to write such an irule for you, but the idea is, for your critical apps, you use that event to detect when a connection sent to a particular pool member fails, and then attempt to select a new member instead of propagating the failure back to the client. You would use some kind of counter to make sure you don't fall into the pit of infinite repetition (if all pool members are down, a naive irule will continue trying to select a new member indefinitely until a pool member is available, so you use a counter that limits reselection attempts to maybe 3, and then propagate the failure back to the client).

If this is not too much work for your requirements, then enjoy the challenge.

This should help: http://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/ltm-monitors-reference-11-6-0.html

Thanks both for your feedback. Based on the link to the documentation the recomemded settings are 5/16 for http monitors, not 30/91 as initially suggested.

Regards,