Rule of thumb for setting GAE front-end instance classes

Question

What is a good rule of thumb for choosing F1, F2 or F4 instance classes on GAE? Ie. when should one start using a higher instance class? Specifically when using Python 2.7 and threadsafe: true (so concurrent requests can be handled).

Answer 1

The easy case is if you simply need more memory. Also, by moving to a higher instance class you "rent" more cpu cycles, so your requests might run until they are finished before you "idle" again. It really depends on the application if it makes sense to switch. There is a section in this Google Developers Video where this is discussed in more detail:

https://www.youtube.com/watch?feature=player_detailpage&v=T_BQevqRp44#t=2094s