When you join a new application is a brand new world, and nothing seems to work as expected. You would like a useful README, some scripts to get you running fast and good documentation. These never happens, but I thing that this new dev will add useful information from that experience as this is not only needed for him to start.

They have to be able to setup the app and find documentation with the source, if they don’t then you have an issue. The application have to be easy to start on development, because if it is not easy it will not be easy to deploy or to scale.

So make sure you can clone the repo and get a working environment with a single command. If there is no single command you should be adding a script. Make a development version of the environment variables available on the repo, to make this even possible.

Move all the configuration to environment variables to make deploys easier to manage. Having a development version of them help documenting them. You can use dotenv to get that with rails.

MYSQLUSER=useful_for_development
MYSQLPASSWORD=password_is_the_same_in_dev_machines

If you need some backend applications then use foreman to start them using a single Procfile (that will then document that):

web:      bundle exec rails server
redis:    redis-server
sidekick: sidekiq -C config/sidekiq.yml

And foreman reads your .env file by default!

Doing this should prevent some headaches later.