Comment on common.sh and its purpose
#! /bin/sh
+
+# This file is useful when you need to run a command on all the Python
+# instances and you don't want to rebuild the image. For example, when
+# working on a feature that requires a new dependency and you need to
+# call: "pip install newdependency==1.4.2". You can add that command
+# here, and it will be executed in all the instances at startup.
