Forum Discussion
danielo303_1961
Nimbostratus
NimbostratusiRule: redirect to pool based on app response time?
I would like to use an iRule to direct traffic based on the response time of the back-end resource pool. Under normal operations, incoming requests (these are SOAP-based queries) will go to the primary resource pool. When the primary pool becomes unresponsive (response slower than 5-10 seconds), requests should be directed to a secondary pool which is configured to basically tell the client "come back later".
I am using priority groups and health monitors to approximate this mechanism currently. But I think if I could find the right tools in iRule I would have more precise control.
Basically I need something like:
when HTTP_REQUEST {
[code to check response time here...]
if response_time < 10 {
pool primary_pool
return
}
else {
pool secondary_pool
return
}
}
Is there a command to test the back-end response? We are on BIG-IP 9.4.3
Thanks!
4 Replies
HamishCirrocumulus
Hmm...
9.4.3 makes it a bit more difficult. I did something for this in 2010 on LDAP servers. But the iRule was designed to be pretty lightweight and the actual calculations for average response times etc was offloaded to a separate server, because different users were expected to have different SLA requirements. (See the LDAP_Stats_Measuring iRule).
The measurements and tracking of response times was tracked by user (ldap bind id), but it required tables. Assuming you don't need that... Hmm.. Not sure. Would need a bit more thought. Any chance you could upgrade to v10.2?
Even then though, you have the problem of working out when the response times decrease again... v11 you could use a sideband connection...
More thought required...
H
hoolioCirrostratus
You could use the after command in 10.0+ to set a timer and select a new pool if the currently selected server doesn't reply. I think you'd need to call LB::detach in the after script and then call the second pool using the pool command.
See the last example on the wiki page for details:
http://devcentral.f5.com/wiki/iRules.after.ashx
http://devcentral.f5.com/wiki/iRules.lb__detach.ashx
Aaron- hoolioOr instead of selecting another pool, you could just send the response content from the iRule itself using HTTP::respond:
http://devcentral.f5.com/wiki/iRules.http__respond.ashx
Aaron 
danielo303_1961Hoolio, Hamish
Thanks so much for the suggestions. Looks like we need to be on 10.0 to really achieve the result we want. I'll tell my boss it's time to upgrade ;-)
Daniel
