HTTP Header Cache Control

This is what I use:

when HTTP_REQUEST {
    set mytime [clock seconds]
    set last_modified "[clock format $mytime -format {%a, %d %b %Y %T %Z} -gmt 1]"
    set cache_control_1 "no-store, no-cache, must-revalidate, max-age=0"
    set cache_control_2 "post-check=0, pre-check=0, false"
    set pragma "no-cache"

    HTTP::respond 503 content {
        
           
              Service Outage Notice
           
           
              This service is currently under maintenance.
           
        
    } "Content-Type" "text/html" "Last-Modified" $last_modified "Cache-Control" $cache_control_1 "Cache-Control" $cache_control_2 "Pragma" $pragma Connection close
}

.