Ruby on Rails生产环境Rack gem常量重复初始化警告及访问异常

Hey there, let's work through this issue together. That Rack constant warning in your Unicorn log is a clue, but the real root cause of the 500 error might be hiding elsewhere. Here's how to debug and fix this step by step:

1. First, Find the Actual 500 Error Cause #

The "something went wrong" message is Rails' generic production error. The Rack warning is probably a side effect, not the main issue. Check your Rails production log for specific details about what's failing:

tail -f /home/nrt/shared/log/production.log

Common culprits here include:

• Missing SECRET_KEY_BASE environment variable (critical for Rails production security)
• Failed database connections (double-check config/database.yml for production credentials)
• Uncompiled assets (ensure bundle exec rake assets:precompile runs during deployment)
• Missing or mismatched gems (verify bundle install --deployment completed successfully)

2. Fix the Rack Constant Conflict #

That "already initialized constant" warning happens when two versions of Rack are being loaded—one from your system's global RVM/gems, and another from your app's bundled gems. To resolve this:

Update Your Unicorn Configuration #

Make sure your config/unicorn.rb forces the use of your app's bundled environment. Add these lines at the top:

# Ensure we use the app's bundled gems exclusively
ENV['BUNDLE_GEMFILE'] = File.expand_path('../Gemfile', __FILE__)
require 'bundler/setup'

Adjust Your Mina Deploy Script #

In config/deploy.rb, ensure you're starting Unicorn with bundle exec to use the app's gem set, not the global one. Your start task should look like this:

task :start do
  queue "cd #{deploy_to}/current && bundle exec unicorn_rails -c config/unicorn.rb -D -E production"
end

Also, make sure Mina loads the correct RVM environment at the top of your deploy script:

set :rvm_path, '/usr/local/rvm/scripts/rvm'
invoke :'rvm:use[ruby-2.1.0@your-app-gemset]' # Replace with your actual Ruby version and gemset name

Clean Up Duplicate Gems #

Navigate to your app's current directory and clean up any conflicting global gems that might be interfering:

cd /home/nrt/current
bundle clean --force
bundle install --deployment

3. Verify Critical Environment Variables #

If your production log mentions missing secrets, generate a SECRET_KEY_BASE and set it on your server:

• Generate the key locally: rake secret
• Add it to your server's environment (e.g., in /etc/profile or your Unicorn startup script):

export SECRET_KEY_BASE="your-generated-secret-key-here"

4. Restart Services #

After making these changes, restart Unicorn (using a smooth restart to avoid downtime) and Nginx (if you're using it as a reverse proxy):

# Smooth restart Unicorn to preserve connections
kill -USR2 $(cat /var/run/unicorn.pid)

# Restart Nginx to apply any config changes
service nginx restart

Go ahead and test your app again after these steps—chances are the 500 error will be resolved, and that Rack warning will disappear too.

内容的提问来源于stack exchange，提问作者Felipe Marcon