My deploy failed, saying "No Procfile found." What should I do?

When we deploy your app, we use a Procfile to determine what services should be run from your app code. The Procfile format is described in detail here, and Heroku has a very helpful article as well.

The Procfile should list process types and the commands associated with them. For example, if you’re running a Rails app with one Sidekiq worker process, you might have the following Procfile:

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web: bundle exec rails server -b 0.0.0.0 -p $PORT
worker: bundle exec sidekiq

This will deploy two sets of containers (“services”) for your app, one for the web process and another for the worker. These services may be scaled independently.