Rails error

Updated 11 October 2026

Short answer

In production, Rails shows a generic "We're sorry, but something went wrong" page and writes the details to its log. By default that's in your app's log/ folder, named after the environment, so log/production.log. On platforms like Heroku, logs go to the platform's log stream instead. Find the exception for the failing request. The usual causes are migrations that didn't run, missing credentials or environment variables, or assets not compiled.

What's the problem

Your Rails app shows "We're sorry, but something went wrong" (500), "The page you were looking for doesn't exist" (404), or fails to boot after a deploy.

Why it happens

  • Pending migrations on production.
  • Missing credentials or environment variables, such as the master key.
  • Assets not precompiled.
  • An exception in a controller or view, often a database or API call.
  • Gem or Ruby version changes.
  • The app server (Puma) crashed behind Nginx (502).

How to fix it

  1. Read log/production.log (or your platform's logs) for the exception.
  2. Run migrations on production.
  3. Check credentials and environment variables.
  4. Precompile assets as part of the deploy.
  5. Check the app server is running and restart it.
  6. Roll back if a deploy caused it.

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Sources

  1. Ruby on Rails: Debugging Rails Applicationsofficial docsBy default, each log is created under Rails.root/log/ and the log file is named after the environment in which the application is running.

Related

500 Internal Server Error Your server hit an error it didn't handle. The cause is in the server's error log: usually a code bug, a bad config change, a failed plugin or a lost database. Heroku error Heroku logs an error code with every failure: H10 app crashed, H12 request timeout, H14 no web dynos, R14 memory exceeded. Run heroku logs to see which. Postgres error Read the message: connection refused, authentication failed, too many connections and statement timeout each point to a different fix. 502 Bad Gateway The server in front of your app got a bad answer, or none, from your app. Usually the app has crashed, isn't running, or is listening on the wrong port.

Preventionlabs is independent and not affiliated with Ruby on Rails. Product names are used only to describe the problem.

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