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Forum Discussion

roykidder's avatar
roykidder
Icon for Nimbostratus rankNimbostratus
Aug 05, 2016

Respond with 5xx message when pool members connection limits reached (iRule?)

I have a use case where I have a pool of web server appliances that, when over loaded, simply time out. I want to set a connection limit on a per-member basis and then be able to hand back a 5xx to t...
application delivery
iRules
LTM
Kai_Wilke's avatar
Kai_Wilke
Icon for MVP rankMVP
Aug 07, 2016

Hi Roy,

if the connection limit of a pool member has been exhausted, the pool member will become temporary marked down, so that it does not receive any new connections attemps. During this time 

[active_members]
do not count nor list the pool member which connection limit is exhausted.

You may try the iRule below. It performs a transparent 

LB::reselect
in the case a pool member has just become unresponsive (but still marked as online) and also displays a 
[HTTP::response 503]
in the case, that all remaining pool members are offline (or having their connection limits exhausted).

when LB_FAILED {
    if { not [info exists "reselect_count"] } then {
        set reselect_count 0
    }
    if { [active_members [LB::server pool]] > $reselect_count } then {
        LB::mode rr
        LB::reselect
        incr reselect_count
    } else {
        HTTP::respond 503 content "The application is too busy to serve your requests..."
        set reselect_count 0
    }
}

Cheers, Kai