No backend match. Environment variables missing for: aws.js, mega.js

After I deploy the current master at Heroku free Dyno, App page shows this:
Application Error An error occurred in the application and your page could not be served. Please try again in a few moments. If you are the application owner, check your logs for details.

And this is the output of heroku logs:
2016-05-05T01:18:00.616224+00:00 heroku[api]: Release v2 created by mandal.sushovan92@gmail.com 2016-05-05T01:18:00.616224+00:00 heroku[api]: Enable Logplex by mandal.sushovan92@gmail.com 2016-05-05T01:19:24.496990+00:00 heroku[api]: Deploy 35c516f by mandal.sushovan92@gmail.com 2016-05-05T01:19:24.496990+00:00 heroku[api]: Release v3 created by mandal.sushovan92@gmail.com 2016-05-05T01:19:24.496245+00:00 heroku[api]: Scale to web=1 by mandal.sushovan92@gmail.com 2016-05-05T01:19:24.962341+00:00 heroku[slug-compiler]: Slug compilation started 2016-05-05T01:19:24.962346+00:00 heroku[slug-compiler]: Slug compilation finished 2016-05-05T01:19:26.916202+00:00 heroku[web.1]: Starting process with commandnode server.js 2016-05-05T01:19:30.554267+00:00 app[web.1]: No backend match. Environment variables missing for: aws.js, mega.js 2016-05-05T01:19:31.638131+00:00 heroku[web.1]: State changed from starting to crashed 2016-05-05T01:19:31.639385+00:00 heroku[web.1]: State changed from crashed to starting 2016-05-05T01:19:31.630398+00:00 heroku[web.1]: Process exited with status 1 2016-05-05T01:19:33.047734+00:00 heroku[web.1]: Starting process with commandnode server.js2016-05-05T01:19:35.259335+00:00 app[web.1]: No backend match. Environment variables missing for: aws.js, mega.js 2016-05-05T01:19:35.968360+00:00 heroku[web.1]: Process exited with status 1 2016-05-05T01:19:35.948261+00:00 heroku[web.1]: State changed from starting to crashed 2016-05-05T01:20:02.174098+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=powerful-woodland-25592.herokuapp.com request_id=d74de48d-8a97-4fc1-b056-c3f806ed09f3 fwd="203.110.242.20" dyno= connect= service= status=503 bytes= 2016-05-05T01:20:03.829016+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/favicon.ico" host=powerful-woodland-25592.herokuapp.com request_id=1a1d3e25-3b7e-45ff-aed5-58a050ebaa06 fwd="203.110.242.20" dyno= connect= service= status=503 bytes= 2016-05-05T01:20:04.873119+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/favicon.ico" host=powerful-woodland-25592.herokuapp.com request_id=2c04d26b-95c0-43fa-9f3f-61fe97f0f478 fwd="203.110.242.20" dyno= connect= service= status=503 bytes=
How to solve this?

Start with server.js and the backend modules named in the log, aws.js and mega.js, to identify which environment variables are required. Reproduce the deployment on Heroku and inspect the logs; done means the process starts without the missing-environment-variable error and the app no longer crashes.