Frequently Asked Questions about Unicorn

Why is nginx getting ECONNRESET as a reverse proxy?

Request body data (commonly from POST and PUT requests) may not be drained entirely by the application. This may happen when request bodies are gzipped, as unicorn reads request body data lazily to avoid overhead from bad requests.

Ref: yhbt.net/unicorn-public/FC91211E-FD32-432C-92FC-0318714C2170@zendesk.com/

Why aren’t my Rails log files rotated when I use SIGUSR1?

The Rails autoflush_log option must remain disabled with multiprocess servers such as unicorn. Buffering in userspace may cause lines to be partially written and lead to corruption in the presence of multiple processes. With reasonable amounts of logging, the performance impact of autoflush_log should be negligible on Linux and other modern kernels.

Why are my redirects going to “http” URLs when my site uses https?

If your site is entirely behind https, then Rack applications that use “rack.url_scheme” can set the following in the Unicorn config file:

HttpRequest::DEFAULTS["rack.url_scheme"] = "https"

For frameworks that do not use “rack.url_scheme”, you can also try setting one or both of the following:

HttpRequest::DEFAULTS["HTTPS"] = "on"
HttpRequest::DEFAULTS["HTTP_X_FORWARDED_PROTO"] = "https"

Otherwise, you can configure your proxy (nginx) to send the “X-Forwarded-Proto: https” header only for parts of the site that use https. For nginx, you can do it with the following line in appropriate “location” blocks of your nginx config file:

proxy_set_header X-Forwarded-Proto https;

Why are log messages from Unicorn are unformatted when using Rails?

Current versions of Rails unfortunately overrides the default Logger formatter.

You can undo this behavior with the default logger in your Unicorn config file:

Configurator::DEFAULTS[:logger].formatter = Logger::Formatter.new

Of course you can specify an entirely different logger as well with the “logger” directive described by ::Unicorn::Configurator.

Why am I getting “connection refused”/502 errors under high load?

Short answer: your application cannot keep up.

You can increase the size of the :backlog parameter if your kernel supports a larger listen() queue, but keep in mind having a large listen queue makes failover to a different machine more difficult.

See the TUNING and ::Unicorn::Configurator documents for more information on :backlog-related topics.

I’ve installed Rack 1.1.x, why can’t Unicorn load Rails (2.3.5)?

Rails 2.3.5 is not compatible with Rack 1.1.x. Unicorn is compatible with both Rack 1.1.x and Rack 1.0.x, and RubyGems will load the latest version of Rack installed on the system. Uninstalling the Rack 1.1.x gem should solve gem loading issues with Rails 2.3.5. Rails 2.3.6 and later correctly support Rack 1.1.x.