unicorn is an HTTP server for Rack applications designed to only serve fast clients on low-latency, high-bandwidth connections and take advantage of features in Unix/Unix-like kernels.
Slow clients should only be served by placing a reverse proxy capable of fully buffering both the the request and response in between unicorn and slow clients.
This is free and open source software.
- Designed for Rack, Unix, fast clients, and ease-of-debugging.
- Compatible with Ruby 2.0.0 and later.
- Process management: unicorn will reap and restart workers that die from broken apps. There is no need to manage multiple processes or ports yourself. unicorn can spawn and manage any number of worker processes you choose to scale to your backend.
- Load balancing is done entirely by the operating system kernel.
- Requests never pile up behind a busy worker process.
- Does not care if your application is thread-safe or not, workers all run within their own isolated address space and only serve one client at a time for maximum robustness.
- Builtin reopening of all log files in your application via USR1 signal. This allows logrotate to rotate files atomically and quickly via rename instead of the racy and slow copytruncate method. unicorn also takes steps to ensure multi-line log entries from one request all stay within the same file.
- nginx-style binary upgrades without losing connections. You can upgrade unicorn, your entire application, libraries and even your Ruby interpreter without dropping clients.
- transparent upgrades using systemd socket activation is supported.
- before_fork and after_fork hooks in case your application has special needs when dealing with forked processes. These should not be needed when the “preload_app” directive is false (the default).
- Can be used with copy-on-write-friendly GC in Ruby 2.0+ to save memory (by setting “preload_app” to true).
- Supports listening on multiple interfaces including UNIX sockets, each worker process can also bind to a private port via the after_fork hook for easy debugging.
- Simple and easy Ruby DSL for configuration.
- Decodes chunked requests on-the-fly.
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