F5 iRule for Header insert

Hi eLeCtRoN do you also have a header named XXX#YYYY? If not, then that's going to be an empty value anyway. If you are trying to:

1. Assure the x-id header exists
2. Assure that the x-id header has a value

Then, something like this should work for you:

when HTTP_REQUEST priority 500 {
    if { [HTTP::header exists x-id] && ([HTTP::header x-id] == "") } { 
        HTTP::header replace x-id "some value here" 
    } else { 
        HTTP::header insert x-id "some value here" 
    } 
}

if you don't need the header to be there then you can eliminate the else statement altogether.