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wsanders_233261's avatar
wsanders_233261
Icon for Nimbostratus rankNimbostratus
Aug 24, 2017

Catching an exception in irule for a nonexistent pool

How would I catch an exception for a nonexistent pool? I have this irule hardwired to return a 503:

 

    when HTTP_REQUEST {
    set HOST [ string tolower [HTTP::host] ]
    set VALUE "/"
    set MYPOOL [ call /Common/LIB-sac-dev::https_rule $HOST $VALUE ]
    log local0.debug "HERE: Pool $MYPOOL Host $HOST Value $VALUE"
    HTTP::respond 503 content "Pool \"$MYPOOL\" unavailable"
    event disable
    TCP::close
    pool $MYPOOL

 

The call returns a pool name according to the host name in the header. If the host name doesn't match a pool, it returns the string "undefined". When MYPOOL exists, the rules correctly responds with a 503:

Unexpectedly, if the pool does not exist, the "pool" statement is evaluated, no 503 response occurs and the browser gets a 'connection reset' instead:

- no such pool: undefined (line 😎 invoked from within "pool $MYPOOL"

How could I send a 503 in response to a ltm rule that contains a reference to a nonexistent pool?

 

application delivery
iRules
  • Kai_Wilke's avatar
    Kai_Wilke
    Icon for MVP rankMVP
    Aug 24, 2017

    Hi Wsanders,

    you may take a look to the iRule below. It uses an 

    if { [catch { some code which may fail }] } then { error handle if code has been failed }

     syntax, to check if the pool name fetched from your datagroup is valid and if the pool has any active members.

     

    when HTTP_REQUEST {

     Getting destination pool name based on HOST and Path

    set HOST [ string tolower [HTTP::host] ]
    set VALUE "/"
    set MYPOOL [ call /Common/LIB-sac-dev::https_rule $HOST $VALUE ]
    log local0.debug "HERE: Pool $MYPOOL Host $HOST Value $VALUE"

     Checking if pool exists and has any active members.

    if { [catch {

         Lets try if the code below works (it will if $MYPOOL contains a valid pool name...) 
        if { [active_members $MYPOOL] == 0 } then {
             The pool does exist but has no available members (aka. no TCL error but [active_members] was equal 0)
            HTTP::respond 503 content "Pool \"$MYPOOL\" is unavailable" "Connection" "close"
            event disable
            TCP::close
        } else {
             The pool does exist and has available members (aka. no TCL error and [active_members] was greater than 0)
            pool $MYPOOL
        }

    }] } then {

         Something went wrong with the code above. Seems that the pool does not exist (aka. a TCL runtime error ocoured)

         log local0.debug "ErrorInfo: [subst "\$::errorInfo"]"
        HTTP::respond 502 content "Bad Gateway - invalid HTTP request" "Connection" "close"
        event disable
        TCP::close

    }
}

     

    Cheers, Kai