unsure what your python deps are - and what are the production deployment? you could include them in the elixir project..
either way for the dev thing maybe look at how GitHub - joshuafleck/ex_ngrok: A wrapper around Ngrok providing a secure tunnel to localhost for demoing your Elixir/Phoenix web application or testing webhook integrations. · GitHub starts up in the dev env - believe it should be applicable in starting up an external app in dev.. (btw - an abstraction of this could be interesting - lots of us are migrating 
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