[enneff]

App Engine is not just a place to run your code. It has a nice deployment system with the ability to flip between versions instantly. It provides a few great pieces of core infrastructure: the datastore, task queues, and memcache (there are many others, but those are the essentials). The SDK gives you a stand-alone development server for testing locally. If you want to build web apps (or a backend for mobile apps), App Engine is a great way to go.

Compute Engine is for all the other stuff that you can't run on App Engine.

Incidentally, the datastore is now available as a stand-alone service, Google Cloud Datastore: https://developers.google.com/datastore/ This should benefit Compute Engine users.

[hrjet]

I like App-Engine and now that there are open-source, API compatible alternatives, there is no lock-in to worry about either.

The biggest drawback for App Engine is lack of async support. The only ways to scale are: multiple-threads (slow) or multiple instances (costly).

[enneff]

Or you can use Go and get high performance concurrency in a single-threaded instance. The best of both worlds. ;-)

[alooPotato]

Can you explain this a bit more? Specifically what async type tasks can you not perform?