Redirect POST data while load balancing GET iRule

I am quite sure I understand your requirement thoroughly. here is what I think it is. you may try

you may change ext_uri variable to be your desired url

 
when RULE_INIT {
    set static::ext_url "http://10.10.71.3/test.post"
}
when HTTP_REQUEST {
        
    if { [string tolower [HTTP::method]] eq "post" } {
        HTTP::collect [HTTP::header "Content-Length"]
    }    
}
when HTTP_REQUEST_DATA {
    set content " \
        "
        
    foreach p [split [HTTP::payload] &] {
        set name  [getfield $p = 1]
        set value [decode_uri [getfield $p = 2]]
        set content "${content}"
    }
    set content "${content}"
   
    HTTP::respond 200 content $content
}

feel free to let me know if you have any question

Nat