Puma review
A free, open-source Ruby server with concurrency, clustering, SSL, and restart controls.
Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
Puma is an open-source web server for Ruby and Rack applications, aimed at teams deploying Ruby services with their applications. It supports MRI Ruby, JRuby, Rubinius, and other Ruby implementations, and runs on Windows, Linux, and self-hosted environments. Its core request handling is multithreaded, with configurable thread pools, while cluster mode adds multiple worker processes. Puma is installed as a Ruby gem rather than operated as a hosted service.
Its strongest fit is the Ruby ecosystem. Integrations include Ruby on Rails, Sinatra, Rack, Bundler, Capistrano, and systemd, giving application teams familiar deployment and service-management connections. The server also supports SSL sockets, TCP and UNIX socket binding, request buffering, WebSockets through partial hijack, and systemd notification and monitoring. Hot and phased restarts help manage application changes, while the built-in control and status server provides operational visibility. Configurable plugins and server-wide hooks extend how the server can be managed around a Ruby application.
Puma is a practical choice for Ruby teams that want free, open-source infrastructure with concurrency, clustering, SSL, monitoring, and restart controls in one server. Its narrow focus is also its clearest boundary: it is designed for Ruby and Rack applications and is deployed with the application rather than consumed as a hosted platform. The published specifications show support for HTTP/1.1, WebSockets, and multiple Ruby implementations, but not HTTP/2 or HTTP/3. Teams building Ruby applications around Rails, Sinatra, or Rack should consider Puma; teams requiring HTTP/2 or HTTP/3 support should choose a server that provides those protocols.
Puma pros and cons
- Where it wins
- Multithreaded handling with configurable thread pools
- Cluster mode supports multiple worker processes
- Rails, Sinatra, Rack, and systemd integrations
- Where it doesn't
- HTTP/2 support is not included
- HTTP/3 support is not included
- Requires deployment with the application as self-hosted software
Puma fact sheet, pricing and score →
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