iRule Variables and Connection Re-Use

Hi John,

TCL session variables will be keept during the duration of the underlying TCP connection. So if you [set variable 1] conditionally and laster use a [info exists variable] to handle those conditional requests, then you have to make sure that you [unset variable] after each single request or at least just within the [info exists variable] code structure.

when HTTP_REQUEST {
    set HOST [HTTP::host]
    set PATH [HTTP::path]

    if { [class match $PATH eq www_redirects] } {
      set ACTION "redirect"
      set VALUE [class match -value $PATH equals www_redirects]
    }
    if { [info exists ACTION] } {
      if { $ACTION eq "redirect" } {
        HTTP::respond 301 "Location" "https://$HOST$VALUE"
      }
      unset $ACTION
    }
}

But the most effective way to support your scenario would be:

1. Reduce $variable usage to an absolute minimum (each of them is eating your CPU and RAM).
2. Avoid [info exists] since it has a somewhat high overhead. You may use [set] on the very beginning of a request to always set/overwrite $variable to a default value (e.g. "") and then check if $variable has a non-default value to handle the conditioal requests.
3. Try to use nested control structures to speed up the execution. Repetive code blocks may look slow, but they are much faster compared to setting variables and then evaluate a variable to trigger additional code blocks.
4. Reduce the [class match] executions to a minimum by skipping the initial data-group entry exist checks. Its far more effective to directly pull the -value for a given data-group entry and then just check if a value could be retrived or not (aka. value not equal ""). While doing so, you may store the output into a $variable for further usage.

Based on the recommendations the most effective code for you scenario would look like that:

when HTTP_REQUEST { if { [set class_uri [class lookup -value [HTTP::path] equals www_redirects]] ne "" } then { HTTP::respond 301 "Location" "https://[HTTP::host]$class_uri" } }

Note: The iRule will query the data-group www_redirects a single time per request and saves the output to $class_uri. If the data-group query got some data back (aka. $class_uri not equal ""), it will directly throw a 301 redirect to the location https://[HTTP::host]$class_uri.

Cheers, Kai