My Rails app is returning HTTP 500 for all its URLs, but nothing shows up in the log file. How can I diagnose the problem?

I have a Rails app that is running on a production server with Apache and Phusion Passenger. The app works fine locally when using Mongrel, but whenever I try to load a URL on the production server, it 开发者_Go百科returns HTTP 500. I know the server is working properly, because I can get the static elements of the application (e.g., JavaScript files, stylesheets, images) just fine. I've also checked the Passenger status and it is loading the app (it must be, since the app's 500 Internal Server Error page is returned, not just the default Apache one). Also, when I load the app via script/console production and do something like app.get("/"), 500 is also returned.

The problem is that there is nothing in the log files to indicate the problem. production.log is empty. The Apache error logs show no problems with Apache, either. I'm stumped as to what's going on and I'm not sure how to diagnose the problem.

I know I may have been a bit vague, but can anyone give a suggestion on what the problem may be? Or at least a way I can go about diagnosing it?

The answer for this specific situation was a problem with my app. One of the model classes used a different database connection than the rest of the app. This database connection was not configured properly. I think the reason why nothing was written to the log files is that Rails bailed out without having any idea what to do.

Since it may be helpful for others to see how I diagnosed this problem, here was my thought process:

1. The issue couldn't be with Apache: no errors were written into the Apache log files.
2. The issue probably wasn't with Passenger: Passenger wasn't writing any errors to the Apache log file, and it seemed to be loading my app properly, since passenger-status showed it as loaded and it was display my app's 500 Internal Server Error page (not the default Apache one).

From there I surmised that it must be something broken in my app that happened very early on in the initialization phase, but wasn't something that caused the app to completely bail and throw an exception. I poked around in the Phusion Passenger Google Group, and ultimately stumbled upon this helpful post, which suggested that the error may be a database connectivity issue. Sure enough, removing this misconfigured database and all references to it made the app work!

Have you tried running the app locally using Passenger?

Try running the application locally on Mongrel in Production mode, to make sure that there's no weird issues with that particular environment. If that works, then you know that it's not an issue with your codebase. Since your static components are being served properly, that tells me that Apache is working fine. The only gear in the system left is Passenger. At this point, I would say it's an improperly configured Passenger. You should post up your Passenger config file, and ask the question on ServerFault.

A couple of things to try :

Have you gone though the following from the docs:

6.3.7. My Rails application’s log file is not being written to

There are a couple things that you should be aware of:

  By default, Phusion Passenger runs Rails applications in production

mode, so please be sure to check production.log instead of development.log. See RailsEnv for configuration. *

  By default, Phusion Passenger runs Rails applications as the owner

of environment.rb. So the log file can only be written to if that user has write permission to the log file. Please chmod or chown your log file accordingly.

  See User switching (security) for details.

If you’re using a RedHat-derived Linux distribution (such as Fedora or CentOS) then it is possible that SELinux is interfering. RedHat’s SELinux policy only allows Apache to read/write directories that have the httpd_sys_content_t security context. Please run the following command to give your Rails application folder that context:

Have you checked your vhost or httpf.conf file ? Do you have any logging directives ?

Check the top level apache log file

Try setting PassengerLogLevel to 1 or 2 or 3, as shown here http://www.modrails.com/documentation/Users%20guide.html#_passengerloglevel_lt_integer_gt

Do you have any rack apps installed ?

My suggestion would be to go right back to "Hello World" land and create the smallest possible Ruby example application and upload it to see if there is a problem with Passenger or Ruby on the server.

May be a silly suggestion but I suggest you start by increasing the logging levels on production while you are testing. Do this in config/environments/production.rb and use:

config.log_level = :debug

This should at least get you some sort of backtrace so you can start to find the problem. If you still get nothing - you may find that you have an issue with something as simple as a missing gem/plugin on your production server. That sort of thing may well manifest as a "500" error and just not be very verbose for you.

Can you run the test suite on your production server?