Reasons NOT to use App Engine

Lately I've been reading a lot of information about App Engine; the Google service that looks very promising to me. However, it all seems too good to be t开发者_如何学编程rue. Call me a negative person, but I would like to know any reasons NOT to use App Engine.

This is programmers related, since I'm asking as in the programmer point of view.

I just want the general "downsides" of App Engine, if any.

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No relational database. (No normal ORM ...)

Limits on the number of files. (Can't just upload the 6,000 files in some standard packages...)

Specific VM required. (Depending on your language you may be a non-starter.)

Runtime limits. (Don't get bogged down.)

SSL only through https://your-app-id.appspot.com (Not directly to your domain.)

Root domains via URL redirection only

I am not criticizing GAE, I'm just listing limitations as the OP asked...

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You are designing your app to a Google-specified framework. Presently you can ONLY run an app-engine application on Google's infrastructure. That means you are completely dependent on Google (at least for the moment). Whether that's a problem or not is dependent on the project in question, but it's something you had best be aware of. Google has been known to cancel things in the past (though that seems unlikely with App Engine).