FAQ

= 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: https://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.