title: Force Google App Engine IP refresh
body: <p>I'm trying to force a Google App Engine app IP address renewal.
  I can only find threads about how to make it static, but I need to do the opposite for security purposes.</p>
  
  <p>I have tried to automatically remove the instances serving my app, but it seems that the old IP is taken by the instance replacing it.
  Maybe it's not possible, anyway, does anybody have a clue on the IP change frequency for a service? </p>
  
  <p>Thanks in advance...</p>