Скачать или смотреть Resolving the 502 Bad Gateway Error with Puma and Nginx in Rails Applications

Struggling with a `502 Bad Gateway` error in your Rails application using Puma and Nginx? Learn how to troubleshoot the connection issues and switch Ruby version managers for a smoother deployment process.
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This video is based on the question https://stackoverflow.com/q/76318243/ asked by the user 'titan' ( https://stackoverflow.com/u/1571115/ ) and on the answer https://stackoverflow.com/a/76343232/ provided by the user 'titan' ( https://stackoverflow.com/u/1571115/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the 502 Bad Gateway Error with Puma and Nginx in Rails Applications

If you’re deploying a Ruby on Rails application on an AWS Lightsail instance and encounter a 502 Bad Gateway error with a message indicating that connection to puma.sock was refused, you’re not alone. This is a common issue for many developers using Nginx as a reverse proxy to handle incoming requests and serve them via Puma, the application server. In this guide, we’ll explore how to resolve this issue and ensure your Rails application is running smoothly.

Understanding the Issue

When you deploy your Rails application, Nginx acts as the intermediary between the internet and your application server (in this case, Puma). A 502 Bad Gateway error typically means that the server was unable to get a valid response from the upstream server (Puma). This can occur for various reasons, but in many cases, it’s due to Puma not running correctly or not being configured properly.

Consider the following symptoms that might indicate why you are experiencing this error:

The error message indicates that it's unable to connect to puma.sock.

A check with the command ps ax | grep puma returns no active Puma processes.

Running cap production puma:status results in a warning that Puma is not running.

No puma.pid file is being created in the /tmp/pids/ directory on your server.

Troubleshooting Steps

To address the connection problem, let’s break down the troubleshooting process.

1. Check Puma’s Status

First and foremost, ensure that Puma is indeed running. You can check its status using Capistrano with the following command:

[[See Video to Reveal this Text or Code Snippet]]

If it returns a warning indicating that Puma is not running, continue to the next step.

2. Restart Puma

If Puma is not running, try restarting it with:

[[See Video to Reveal this Text or Code Snippet]]

Observe the output carefully to ensure that it indicates Puma has started correctly. If you see messages confirming that Puma is listening on the socket, you would usually expect it to be operational.

3. Check for Errors in Logs

After attempting a restart, go through the puma_error.log for any messages that could help diagnose the issue. Look for connection errors or misconfigurations that prevent Puma from starting.

4. Investigate the Ruby Environment

One common reason for these issues is the environment set up for running your application. In this case, the original setup was using rbenv as the Ruby version manager. After some investigation, it was discovered that rbenv was not properly identifying the application's current directory as a Rails application.

Switching from rbenv to rvm

A resolution to the problem was switching from rbenv to rvm (Ruby Version Manager). Here’s why this worked:

Environment Configuration: rvm was able to correctly recognize the Rails environment and managed to run the Puma application without any issues.

Command Execution: Upon trying to run rails s -e production in the current directory, it provided only the template command response, indicating a deeper issue with the Rails command invocation under rbenv.

By switching to rvm, the problem was resolved, and Puma started up as expected without further connection issues.

Conclusion

Encountering the 502 Bad Gateway error when deploying a Rails application might be frustrating, but with the right approach, you can troubleshoot and resolve the underlying issues. This case highlighted the importance of the Ruby version manager in correctly setting up the environment for running your application.

If you find yourself in