H2O

Original author(s)	Kazuho Oku [ja] DeNA
Initial release	February 18, 2015; 9 years ago (2015-02-18)[1]
Stable release	2.2.6 / August 13, 2019; 4 years ago (2019-08-13)[2]
Repository	github.com/h2o/h2o
Written in	C
Operating system	Unix-like
Type	Web server
License	MIT License
Website	h2o.examp1e.net

H2O is a free and open-source web server. It is written in C, and is distributed under the terms of the MIT License.

It was designed with a focus on supporting HTTP/2 and TLS, maximizing the use of new web technologies such as prioritization and server push. As a result it achieves significantly better performance than conventional web servers such as nginx.^[3]

Features

H2O has the following key features:^[4]

• HTTP/1.0 and HTTP/1.1 support
• HTTP/2 support
  • Full support for dependency and weight-based prioritization with server-side tweaks
  • Cache-aware server push
• HTTP/3 support (experimental)
• TCP Fast Open
• TLS support
  • Session resumption (standalone and memcached)
  • Session tickets with automatic key rollover
  • Automatic OCSP stapling
  • Forward secrecy and fast AEAD cipher suite
  • Private key protection using privilege separation
  • Encrypted Client Hello (experimental)^[5]
• Static file serving
• FastCGI support
• Reverse proxy
• Scripting using mruby (Rack-based)
• Graceful restart and self-upgrade

History

In July 2014, Kazuho Oku [ja] started development of H2O for usage as a server for mobile games while working at DeNA.^[6] The initial version was released in December 2014, and the first stable version was released in February 2015 when the HTTP/2 specification was finalized.^[7]