Heroku deployment in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when you run heroku run rails db:migrate?

After deploying a Rails app to Heroku, you run heroku run rails db:migrate. What does this command do?

A It runs the database migrations on the Heroku production database.

B It runs migrations locally on your computer's database.

C It restarts the Heroku app without running migrations.

D It deletes the Heroku database and creates a new one.

💡 Hint

Think about where the app is running and where the database lives on Heroku.

The command heroku run rails db:migrate runs migrations on the Heroku app's production database, updating its schema.

📝 Syntax

intermediate

Which Procfile entry correctly starts a Rails web server on Heroku?

You want to tell Heroku how to start your Rails app web server. Which Procfile line is correct?

A web: rails server -p 3000

B web: bundle exec rails server -p $PORT

C web: rails start

D web: bundle exec puma

💡 Hint

Heroku assigns a port dynamically. The command must use that port.

The correct Procfile entry uses $PORT so Heroku can assign the port dynamically. It also uses bundle exec rails server to start the server.

🔧 Debug

advanced

Why does this Heroku deployment fail with a PG::ConnectionBad error?

You deployed your Rails app to Heroku but get this error in logs: PG::ConnectionBad: could not connect to server. What is the most likely cause?

A The <code>DATABASE_URL</code> environment variable is missing or incorrect.

B The Rails app is missing the <code>sqlite3</code> gem in production.

C The <code>Procfile</code> is missing the web server command.

D The <code>Gemfile.lock</code> is not committed to git.

💡 Hint

Heroku uses DATABASE_URL to connect to the database.

The error means the app cannot connect to the Postgres database. Usually, this happens if DATABASE_URL is missing or wrong.

❓ state_output

advanced

What is the effect of running heroku config:set RAILS_ENV=production?

You run heroku config:set RAILS_ENV=production on your app. What does this change do?

A It restarts the app without changing any environment variables.

B It disables asset precompilation during deployment.

C It sets the environment variable only for your local machine.

D It sets the Rails environment to production on Heroku, affecting config and logging.

💡 Hint

Environment variables on Heroku control app behavior in the cloud.

Setting RAILS_ENV=production on Heroku tells Rails to run in production mode, which changes logging, caching, and other settings.

🧠 Conceptual

expert

Why must you precompile assets before deploying a Rails app to Heroku?

Rails uses asset precompilation before deployment. Why is this step necessary on Heroku?

A To create database indexes for faster queries on Heroku Postgres.

B To convert Ruby code into JavaScript for Heroku's server environment.

C To generate optimized CSS and JavaScript files so the app loads faster in browsers.

D To install all gems needed by the app before deployment.

💡 Hint

Think about what assets are and how browsers use them.

Precompiling assets creates optimized CSS and JS files that browsers can load quickly, improving app performance on Heroku.