Help with iRule

Okay, so basically it looks like this. Let's assume the incoming URI is /pool1/foo/bar and the virtual server is test_vs.

when HTTP_REQUEST priority 100 {
    set poolId [string range [HTTP::uri] 1 [expr [string first "/" [HTTP::uri] 1]-1]]
     This grabs the first part of the URI ("pool1") and assigns it to a variable. So string range, starting at the second character (/ is 0), and stopping at the first occurrence of "/".

    set poolIdLen [string length $poolId]
     This sets the length of the above string, in this case 5.

    set newUri "[string range [HTTP::uri] [expr $poolIdLen+1] end]"
     This grabs everything after the first section (/foo/bar), which will become the new URI that gets passed to the application. So string range, starting at character 6 (5 + 1), going all the way to the end.

    set uriPoolMapClass "[string range [virtual name] 0 end-2]uri_pool_map_class"
     This creates a string based on the virtual server name (test_vs), minus the last two characters in the name (so "test_"), then appends that to the string "uri_pool_map_class", which should in this case derive the string "test_uri_pool_map_class". Presumably there's a data group named this, and inside the data group is a key-value pair, where the key is the poolId value and the value is the actual pool name.

    set dstPool [class lookup [string tolower $poolId] $uriPoolMapClass]
     This grabs the real pool name from the data group based on the poolId value passed in the URI.

    if {$dstPool ne ""} {
         Hash out next line to disable logging
         log local0.debug "poolId: $poolId | poolIdLen: $poolIdLen | newUri: $newUri | dgl_name: $uriPoolMapClass dstPool: $dstPool"
        HTTP::uri $newUri
        pool $dstPool
         Assuming there's a data group match, change the inbound URI to the server to newURI value (/foo/bar), and pool to the matched pool name.

    } else {
         Hash out next line to disable logging
         log local0.debug "poolId: $poolId | poolIdLen: $poolIdLen | newUri: $newUri | no pool set"
         TODO this needs to be changed to reject if there isn't another iRule which ends in a deny_all
        return
         Otherwise just use the pool that's assigned to the VIP.

    }
}

The whole point of this iRule is to allow an application to dictate which pool to send traffic to by injecting the pool into the URL.

Hi,

here are some improvements of the code with comments

when CLIENT_ACCEPTED {
     define the datagroup name based on virtual server.
     It is recommended to do it once per TCP connection (event CLIENT_ACCEPTED) instead of per request (event HTTP_REQUEST)
    set uriPoolMapClass "[string range [virtual name] 0 end-2]uri_pool_map_class"
}

when HTTP_REQUEST priority 100 {
     decode URI to provision both poolId and newUri variables.
    switch [scan [HTTP::uri] {/%[^/]%s} poolId newUri] {
        0 {
            Pool ID not available
            return
        }
        1 {
             Pool ID available, but newUri not set. setting  newUri to /
             this happens when URI is like "/poolId" and not "/poolId/path1/path2"
            set newUri "/"
        }
        2 {
             Everything seems OK. continue.
        }
    }
    
    if {[set dstPool [class lookup [string tolower $poolId] $uriPoolMapClass]] ne ""} {
        HTTP::uri $newUri
        if {[catch {pool $dstPool}] {
             Pool assignment fails. it may not exist and create a TCL error if not inside catch command.
             define action here for this behavior.
             this happens if poolId is already created in Datagroup but the pool is not created yet.
        }
    } else {
         TODO this needs to be changed to reject if there isn't another iRule which ends in a deny_all
        return
    }
}