title: Firebase Functions to GCE firewall rule
body: <p>I have some firebase functions that have to connect to a REST service running on a GCE machine in GCP (under the same project of course). The firewall is blocking the connection and the only way to make it happen was to open the port to everybody. </p>
  
  <p>Does anybody know how can you specify firebase functions as source in a firewall rule?</p>