Rewriting multiple values of HTTP Location header

Hello Frédéric, do you need a redirect from first URL to second URL? 

Will the two URLs always be the same or is there a whole subfolder content to be redirected?

In first case, in my opinion a LTM policy configured for static redirect will just work fine.

In second case, there's a few ways to do it depending on the requirements.

If there's a big list of URLs to be handled, you might want to work with Data Groups to keep it simple. Configure a string-type DG like this:

ltm data-group internal /Common/datagroup_path_rewrite {
 records {
 /oldsubfolder1/ { }
 /oldsubfolder2/ { }
 /oldsubfolder3/ { }
 /oldsubfolder4/ { }
 /oldsubfolder5/ { }
 }
 type string
}

Then use it in an iRule for path replacement

when HTTP_REQUEST {

  if {[string tolower [HTTP::host]] eq "myorighost:81" } {
    HTTP::header replace Host "myrewritedhost"
    # this is not a redirect
  }

  # read as: does the uri contain an element of datagroup_path_rewrite (case sensitive)
  if {[class match [HTTP::uri] contains datagroup_path_rewrite]} {

    HTTP::path /analytics/Portal/jsp/html/portal/portal.js
    # this rewrites the URI path before senting traffic to BE server
  }
}

Also, I've recently answered a similar question in this thread, see if this helps as well.