Debug Heroku Deployment Errors: Slay Asset Compilation & Env Vars Dragons ?

[Sascha]

You just typed git push heroku main with confidence.

Then... BOOM.

ERROR: Asset compilation failed or ENV_VAR not set.

Sound familiar? Let’s fix these deployment gremlins once and for all.

1. Asset Compilation: The Silent Killer (in Rails)


Why it fails:

• Missing dependencies (e.g., yarn not installed)
• Outdated Node/Ruby versions
• Path issues in deployment environment

The Fix:


# Precompile assets locally before deploying:
RAILS_ENV=production bundle exec rails assets:precompile

# Ensure Node.js & Yarn in deployment:
heroku buildpacks:add --index 1 heroku/nodejs
heroku buildpacks:add --index 2 heroku/ruby




Pro Tip: Add to package.json:


{
"scripts": {
"postinstall": "rails assets:precompile"
}
}



2. Environment Variables: The "It Works on My Machine" Trap


Classic Errors:

• Forgetting to set RAILS_ENV=production
• Typo in variable name (SECRET_KEY_BASE vs SECRET_KEY_BAS)
• Not restarting dynos after setting vars

The Fix:


# Set and VERIFY:
heroku config:set RAILS_ENV=production SECRET_KEY_BASE=$(rake secret)
heroku config:get SECRET_KEY_BASE # Double-check!
heroku restart




Debugging Pro Move:


# config/initializers/env_check.rb
raise "SECRET_KEY_BASE missing!" if ENV["SECRET_KEY_BASE"].nil?



3. Other Deployment Demons ?

Database Setup Fail


Symptom: PG::ConnectionBad

Fix:


heroku run rails db:migrate # ← Often forgotten!



File Permission Nightmares


Symptom: EACCES: permission denied

Fix:


# In Dockerfile:
RUN chown -R app:app /app



Memory Limits (Asset Compilation)


Fix:


# Heroku
heroku config:set NODE_OPTIONS="--max_old_space_size=2048"



4. Your Deployment Survival Kit

1. Logs Are Oxygen:

heroku logs --tail # Live view

1. Reproduce Locally:

RAILS_ENV=production bundle exec rails assets:precompile

1. Staging Environment:

heroku create my-app-staging --remote staging



Real War Story


Last week, I spent 3 hours debugging why CSS wasn’t loading.

Cause: Precompilation failed silently.

Solution:


heroku run rails assets:clean # Cleared cached garbage



Your Turn


Next time deployment fails:

1. Don’t panic
2. Check logs
3. Verify assets + env vars
4. Slay the dragon ?

Got a deployment horror story? Share below! ?

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