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Forum Discussion

ZacW's avatar
ZacW
Icon for Nimbostratus rankNimbostratus
Dec 07, 2015

LB_FAILED iRule vs HTTP Fallback Host

Hello,   I'm working on creating a splash page for a URL which will be used as a maintenance page and a redirection for when pool members are unavailable. I've used an iRule in the past which use...
application delivery
iRules
LTM
sfuerst_116779's avatar
sfuerst_116779
Historic F5 Account
Dec 07, 2015

LB_FAILED occurs when the proxy fails to connect to a server in a pool.

 

Anything that raises an abort above the HTTP filter in the chain will trigger a HTTP fallback. This includes things like errors in iRules, Out of Memory situations, misconfiguration, and of course the proxy failing to connect.

 

The LB_FAILED event allows you to execute arbitrary TCL code in an iRule. You can log, you can respond, you can try a re-pick in a different pool etc. The Fallback case is much more limited, as it will only send a pre-canned response.