ACE http health probes - best practice for interval and passdetect interval?

[bgfl-tech]

Hi,

Is there a recommended standard for http health probes in terms of interval and passdetect interval timings, i.e. should the passdetect interval always be less than the interval or visa versa? Can a http probe be 'mis-configured', i.e. return a 'false positive' by configuring an interval timeout thats 'incompatible' with the device it's polling?

I have a http probe for a serverfarm consisting of two Apache http servers and get intermittent 'server reply timeout' probe failures. I'm keen to ensure that the configuration of the probe isn't at fault so I can be confident that a failed probe indicates a problem with the server and not my configuration.

The probe is currently configured as below:-

probe http http-apache
  interval 30
  passdetect interval 15
  passdetect count 6
  request method get url /cs/images/ACE.html
  expect status 200 304

Any advice on the subject woud be gratefully received.

thanks

Matthew

[Gilles Dufour]

Matthew,

there is no magic value here.

Usually, this is your SLA that is important.

If you guarantee that your website will be down no longer than 1minute, obviously you can't have a 2 minutes probe frequency.

If you have no SLA, than what you have is good.  don't change it.

If your SLA is very low like 3 seconds.

The problem is how many servers do you have ?

Too many probes is going to slow down the ACE CP processor.

Gilles.

[bgfl-tech]

Hi Gilles,

Thanks for the advice. In another dicussion (found here https://supportforums.cisco.com/message/462397#462397) a poster has stated that:-

"(The) "Probe interval" should always be less then (open+recieve) timeout  value. Default open & receive timeouts are 10 seconds."

Are you able to advise on whether the above is correct and if so, why? I currently have an interval value of 30 that obviously goes against the advice above (which I've interpretted to mean that if you leave the open & receive timeouts at their default settings your probe interval should be less than 20 seconds?).

thanks

Matthew