Heroku deployment in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Heroku in the context of Rails applications?

Heroku is a cloud platform that lets you deploy, run, and manage Rails apps easily without managing servers.

beginner

Which command initializes a new Git repository if you don't have one before deploying to Heroku?

git init initializes a new Git repository in your project folder.

intermediate

Why do you need a Procfile in a Rails app for Heroku deployment?

A Procfile tells Heroku how to start your app, usually by running the web server.

intermediate

What is the purpose of running heroku run rails db:migrate after deployment?

It runs database migrations on the Heroku server to update the database schema to match your app.

intermediate

How do you set environment variables like secret keys on Heroku?

Use heroku config:set KEY=VALUE to securely set environment variables for your app.

What is the first step to deploy a Rails app to Heroku?

A Create a Git repository

B Run <code>rails server</code>

C Install Node.js

D Write a Dockerfile

Heroku uses Git to deploy apps, so you must have a Git repository first.

Which file tells Heroku how to start your Rails app?

A Procfile

B database.yml

C Gemfile

D config.ru

The Procfile specifies the command Heroku runs to start your app.

How do you push your code to Heroku for deployment?

A rails deploy

B git push heroku main

C heroku deploy

D git push origin main

You push your code to the Heroku remote repository using git push heroku main.

What command runs database migrations on Heroku?

A heroku migrate

B rails db:migrate

C heroku run rails db:migrate

D git migrate

You run migrations on Heroku with heroku run rails db:migrate.

How do you set a secret key environment variable on Heroku?

A git config secret_key abc123

B heroku set secret_key=abc123

C rails secret set abc123

D heroku config:set SECRET_KEY=abc123

Use heroku config:set to set environment variables securely.

Explain the steps to deploy a Rails app to Heroku from a local project.

Think about preparing your app, connecting to Heroku, and updating the database.

Describe how environment variables are managed in Heroku for a Rails app.

Consider how to keep secrets safe and accessible in production.

Practice

1. What is the main purpose of deploying a Rails app to Heroku?

easy

A. To put the app online without managing servers

B. To write Ruby code faster

C. To create a local database

D. To debug Rails code automatically

Solution

1. Step 1: Understand Heroku's role

   Heroku is a platform that hosts apps so they can be accessed online without you managing the servers.

2. Step 2: Compare options

   Options B, C, and D describe development or debugging tasks, not deployment.

3. Final Answer:

   To put the app online without managing servers -> Option A

4. Quick Check:

   Heroku deployment = online app hosting [OK]

Hint: Heroku hosts apps online, no server setup needed [OK]

Common Mistakes:

• Confusing deployment with coding or debugging
• Thinking Heroku manages local databases
• Assuming Heroku speeds up writing code

2. Which command is used to push your Rails app code to Heroku?

easy

A. heroku push

B. heroku deploy app

C. rails deploy

D. git push heroku main

Solution

1. Step 1: Identify the correct git command

   Heroku uses git to receive code. The correct command is 'git push heroku main' to push the main branch.

2. Step 2: Check other options

   Options A, C, and D are not valid commands for pushing code to Heroku.

3. Final Answer:

   git push heroku main -> Option D

4. Quick Check:

   Push code with git push heroku main [OK]

Hint: Use git push heroku main to deploy code [OK]

Common Mistakes:

• Using 'heroku push' which is invalid
• Trying 'rails deploy' which doesn't exist
• Confusing Heroku CLI commands

3. After pushing your Rails app to Heroku, which command runs database migrations on Heroku?

medium

A. heroku run rails db:migrate

B. rails db:migrate

C. git migrate heroku

D. heroku migrate db

Solution

1. Step 1: Understand migration on Heroku

   To run migrations on Heroku's remote server, you use 'heroku run rails db:migrate'.

2. Step 2: Check other commands

   'rails db:migrate' runs locally, 'git migrate heroku' and 'heroku migrate db' are invalid commands.

3. Final Answer:

   heroku run rails db:migrate -> Option A

4. Quick Check:

   Run migrations remotely with heroku run rails db:migrate [OK]

Hint: Run migrations remotely with heroku run rails db:migrate [OK]

Common Mistakes:

• Running migrations locally instead of on Heroku
• Using invalid git commands for migration
• Confusing command order

4. You pushed your Rails app to Heroku but see an error when opening the app URL. What is a common cause?

medium

A. You did not install Ruby locally

B. You used 'git push origin main' instead of 'git push heroku main'

C. You forgot to run database migrations on Heroku

D. You opened the wrong browser

Solution

1. Step 1: Identify common deployment errors

   Forgetting to run migrations on Heroku often causes errors because the database schema is not updated.

2. Step 2: Evaluate other options

   You used 'git push origin main' instead of 'git push heroku main' means code wasn't pushed to Heroku, but question says code was pushed. Options A and D are unrelated to deployment errors.

3. Final Answer:

   You forgot to run database migrations on Heroku -> Option C

4. Quick Check:

   Missing migrations cause app errors on Heroku [OK]

Hint: Run migrations after push to avoid errors [OK]

Common Mistakes:

• Ignoring migrations after deployment
• Confusing git push origin with heroku
• Blaming local environment for Heroku errors

5. You want to deploy a Rails app with environment variables for API keys on Heroku. Which is the correct way to set them before deployment?

hard

A. Add keys to config/application.rb file

B. Use 'heroku config:set KEY=value' command

C. Store keys in a local .env file only

D. Push keys directly in your code files

Solution

1. Step 1: Understand environment variables on Heroku

   Heroku uses 'heroku config:set' to securely store environment variables like API keys.

2. Step 2: Evaluate other options

   Adding keys to config/application.rb or pushing keys in code risks exposure. Local .env files are not sent to Heroku.

3. Final Answer:

   Use 'heroku config:set KEY=value' command -> Option B

4. Quick Check:

   Set env vars securely with heroku config:set [OK]

Hint: Use heroku config:set to add env variables securely [OK]

Common Mistakes:

• Hardcoding keys in code risking leaks
• Relying on local .env files for Heroku
• Editing config/application.rb for secrets