# Puma: A Ruby Web Server Built For Concurrency [](https://gitter.im/puma/puma?utm\_source=badge&utm\_medium=badge&utm\_campaign=pr-badge) [](http://travis-ci.org/puma/puma) [](https://ci.appveyor.com/project/nateberkopec/puma) [](https://gemnasium.com/puma/puma) [](https://codeclimate.com/github/puma/puma) Puma is a **simple, fast, threaded, and highly concurrent HTTP 1.1 server for Ruby/Rack applications** in development and production. ## Built For Speed & Concurrency Under the hood, Puma processes requests using a C-optimized Ragel extension (inherited from Mongrel) that provides fast, accurate HTTP 1.1 protocol parsing in a portable way. Puma then serves the request in a thread from an internal thread pool. Since each request is served in a separate thread, truly concurrent Ruby implementations (JRuby, Rubinius) will use all available CPU cores. Puma was designed to be the go-to server for [Rubinius](http://rubini.us), but also works well with JRuby and MRI. On MRI, there is a Global VM Lock (GVL) that ensures only one thread can run Ruby code at a time. But if you're doing a lot of blocking IO (such as HTTP calls to external APIs like Twitter), Puma still improves MRI's throughput by allowing blocking IO to be run concurrently. ## Quick Start ``` $ gem install puma $ puma ``` ## Frameworks ### Rails Puma is the default server for Rails, and should already be included in your Gemfile. Then start your server with the `rails` command: ``` $ rails s ``` Many configuration options are not available when using `rails s`. It is recommended that you use Puma's executable instead: ``` $ bundle exec puma ``` ### Sinatra You can run your Sinatra application with Puma from the command line like this: ``` $ ruby app.rb -s Puma ``` Or you can configure your application to always use Puma: ```ruby require 'sinatra' configure { set :server, :puma } ``` ## Configuration Puma provides numerous options. Consult `puma -h` (or `puma --help`) for a full list of CLI options, or see [dsl.rb](https://github.com/puma/puma/blob/master/lib/puma/dsl.rb). ### Thread Pool Puma uses a thread pool. You can set the minimum and maximum number of threads that are available in the pool with the `-t` (or `--threads`) flag: ``` $ puma -t 8:32 ``` Puma will automatically scale the number of threads, from the minimum until it caps out at the maximum, based on how much traffic is present. The current default is `0:16`. Feel free to experiment, but be careful not to set the number of maximum threads to a large number, as you may exhaust resources on the system (or hit resource limits). ### Clustered mode Puma also offers "clustered mode". Clustered mode `fork`s workers from a master process. Each child process still has its own thread pool. You can tune the number of workers with the `-w` (or `--workers`) flag: ``` $ puma -t 8:32 -w 3 ``` Note that threads are still used in clustered mode, and the `-t` thread flag setting is per worker, so `-w 2 -t 16:16` will spawn 32 threads in total. In clustered mode, Puma may "preload" your application. This loads all the application code *prior* to forking. Preloading reduces total memory usage of your application via an operating system feature called [copy-on-write](https://en.wikipedia.org/wiki/Copy-on-write) (Ruby 2.0+ only). Use the `--preload` flag from the command line: ``` $ puma -w 3 --preload ``` If you're using a configuration file, use the `preload_app!` method: ```ruby # config/puma.rb workers 3 preload_app! ``` Additionally, you can specify a block in your configuration file that will be run on boot of each worker: ```ruby # config/puma.rb on_worker_boot do # configuration here end ``` This code can be used to setup the process before booting the application, allowing you to do some Puma-specific things that you don't want to embed in your application. For instance, you could fire a log notification that a worker booted or send something to statsd. This can be called multiple times. If you're preloading your application and using ActiveRecord, it's recommended that you setup your connection pool here: ```ruby # config/puma.rb on_worker_boot do ActiveSupport.on_load(:active_record) do ActiveRecord::Base.establish_connection end end ``` On top of that, you can specify a block in your configuration file that will be run before workers are forked: ```ruby # config/puma.rb before_fork do # configuration here end ``` Preloading can’t be used with phased restart, since phased restart kills and restarts workers one-by-one, and preload_app copies the code of master into the workers. ### Binding TCP / Sockets In contrast to many other server configs which require multiple flags, Puma simply uses one URI parameter with the `-b` (or `--bind`) flag: ``` $ puma -b tcp://127.0.0.1:9292 ``` Want to use UNIX Sockets instead of TCP (which can provide a 5-10% performance boost)? ``` $ puma -b unix:///var/run/puma.sock ``` If you need to change the permissions of the UNIX socket, just add a umask parameter: ``` $ puma -b 'unix:///var/run/puma.sock?umask=0111' ``` Need a bit of security? Use SSL sockets: ``` $ puma -b 'ssl://127.0.0.1:9292?key=path_to_key&cert=path_to_cert' ``` ### Control/Status Server Puma has a built-in status/control app that can be used to query and control Puma itself. ``` $ puma --control tcp://127.0.0.1:9293 --control-token foo ``` Puma will start the control server on localhost port 9293. All requests to the control server will need to include `token=foo` as a query parameter. This allows for simple authentication. Check out [status.rb](https://github.com/puma/puma/blob/master/lib/puma/app/status.rb) to see what the app has available. You can also interact with the control server via `pumactl`. This command will restart Puma: ``` $ pumactl restart --control-token foo ``` To see a list of `pumactl` options, use `pumactl --help`. ### Configuration File You can also provide a configuration file which Puma will use with the `-C` (or `--config`) flag: ``` $ puma -C /path/to/config ``` If no configuration file is specified, Puma will look for a configuration file at `config/puma.rb`. If an environment is specified, either via the `-e` and `--environment` flags, or through the `RACK_ENV` environment variable, the default file location will be `config/puma/environment_name.rb`. If you want to prevent Puma from looking for a configuration file in those locations, provide a dash as the argument to the `-C` (or `--config`) flag: ``` $ puma -C "-" ``` Take the following [sample configuration](https://github.com/puma/puma/blob/master/examples/config.rb) as inspiration or check out [dsl.rb](https://github.com/puma/puma/blob/master/lib/puma/dsl.rb) to see all available options. ## Restart Puma includes the ability to restart itself. When available (MRI, Rubinius, JRuby), Puma performs a "hot restart". This is the same functionality available in *Unicorn* and *NGINX* which keep the server sockets open between restarts. This makes sure that no pending requests are dropped while the restart is taking place. For more, see the [restart documentation](https://github.com/puma/puma/blob/master/docs/restart.md). ## Signals Puma responds to several signals. A detailed guide to using UNIX signals with Puma can be found in the [signals documentation](https://github.com/puma/puma/blob/master/docs/signals.md). ## Platform Constraints Some platforms do not support all Puma features. * **JRuby**, **Windows**: server sockets are not seamless on restart, they must be closed and reopened. These platforms have no way to pass descriptors into a new process that is exposed to Ruby. Also, cluster mode is not supported due to a lack of fork(2). * **Windows**: daemon mode is not supported due to a lack of fork(2). ## Known Bugs For MRI versions 2.2.7, 2.3.4 and 2.4.1, you may see ```stream closed in another thread (IOError)```. It may be caused by a [Ruby bug](https://bugs.ruby-lang.org/issues/13632). It can be fixed with the gem https://rubygems.org/gems/stopgap_13632: ```ruby if %w(2.2.7 2.3.4 2.4.1).include? RUBY_VERSION gem "stopgap_13632", "~> 1.0", :platforms => ["mri", "mingw", "x64_mingw"] end ``` ## Deployment Puma has support for Capistrano with an [external gem](https://github.com/seuros/capistrano-puma). It is common to use process monitors with Puma. Modern process monitors like systemd or upstart provide continuous monitoring and restarts for increased reliability in production environments: * [tools/jungle](https://github.com/puma/puma/tree/master/tools/jungle) for sysvinit (init.d) and upstart * [docs/systemd](https://github.com/puma/puma/blob/master/docs/systemd.md) ## Contributing To run the test suite: ```bash $ bundle install $ bundle exec rake ``` ## License Puma is copyright Evan Phoenix and contributors, licensed under the BSD 3-Clause license. See the included LICENSE file for details.