App engine "modules" are a new (and experimental, and confusingly-named) feature in App Engine: https://developers.google.com/appengine/docs/python/modules. Developers are being urged to convert use of the "backends" feature to use of this new feature.
There seem to be two ways to start an instance of a module: to send a HTTP request to it (i.e. at http://modulename.appname.appspot.com for the appname application and modulename module), or to call google.appengine.api.modules.start_module().
The Simple Way
The simple way to start an instance of a module would seem to be to create an HTTP request. However, in my case this results in only two outcomes, neither of which is what I want:
If I use the name of the backend that my application defines, i.e. http://backend.appname.appspot.com, the request is properly routed to the backend and properly denied (because backend access is defined by default to be private).
Anything else results in the request being routed to the sole frontend instance of the default module, even using random character strings as module names, such as http://sdlsdjfsldfsdf.appname.appspot.com. This even holds for made-up instance IDs such as in the case of http://99.sdlsdjfsldfsdf.appname.appspot.com, etc. And of course (this is the problem) for the actual name of my module as well.
Starting via the API
The documentation says that calling start_module() with the name of a module and version should cause the specified version of the specified module to start up. However, I'm getting an UnexpectedStateError whenever I call this function with valid arguments.
The Unfortunate State of Affairs
Because I can't get this to work, I'm wondering if there is some subtlety that the documentation might not have mentioned. My setup is pretty straightforward, so I'm wondering if this is a widespread problem to which someone has found a solution.
It turns out that versions cannot be numeric. This problem seems to have been happening because our module's version was "1" and not (for example) "v1".