I have a production server with nginx -> unicorn -> rails. I precompile assets, which puts assets in public/assets with a fingerprint (hash) appended to the filename. However, when a web page is requested, references to application.css and application.js assets will have the wrong fingerprint. For example, the rails helper stylesheet_link_tag will generate a filename that does not exist in public/assets on the server, because the requested fingerprint does not match the precompiled one. Image assets work fine (fingerprints match).
Troubleshooting this, I precompiled assets on my local machine, and the fingerprint matches the precompiled fingerprint on my server. Moreover, when running locally with webrick in production mode, everything works. I then tried running webrick on my server, which worked, making me think unicorn is the source of the problem.
I have solved this problem by starting unicorn with the --no-default-middleware (or -N) option, and this makes unicorn behave as expected with respect to precompiled assets. My understanding is that this tells unicorn not to load a default set of Rack middleware that it would otherwise load. However, I don't really understand why this solves the problem, or what is going wrong in the first place. What is going on?
Some specifics: Ubuntu 12.04, Rails 4.0.1, Ruby 2.1.0, bootstrap 3.0 with a third party theme
The reason that I don't believe this is an nginx problem is that when I request the page from a browser, and then view source, the filename for the application.css file has a fingerprint, so it actually looks like application-3855b1928b94aa5bff5e1dac1aa56882.css. This does not match the real fingerprint of the file on my server. I am convinced that the fingerprint on the server is correct because I get the same fingerprint on my local development machine. So the client is loading the web page, then asking the server for the .css file...nginx receives that request, but can't find the .css file, because it actually isn't there, so nginx is behaving as expected.
The fingerprint is generated twice: Once when I precompile assets, which is working correctly (pretty sure), and is happening with no unicorn involvement. And a second time, when rails in the context of a unicorn worker sees the stylesheet_link_tag helper and on-the-fly calculates the fingerprint (I think this is what it's doing), which for some reason is generating an incorrect fingerprint. This same process happens if I replace unicorn with webrick on the exact same server, but in this case the fingerprints match. If I start unicorn with the -N flag, the fingerprints match, but I don't know why this makes a difference, and I don't know why nobody else seems to have to do this.