nginx ("engine x") is an HTTP web server, reverse proxy, content cache, load balancer, TCP/UDP proxy server, and mail proxy server. Originally written by Igor Sysoev and distributed under the 2-clause BSD License. Enterprise distributions, commercial support and training are available from F5, Inc. Nginx may be configured to serve static web content or to act as a proxy server. Nginx can be deployed to also serve dynamic content on the network using FastCGI, SCGI handlers for scripts, WSGI application servers or Phusion Passenger modules, and can serve as a software load balancer. Nginx uses an asynchronous event-driven approach, rather than threads, to handle requests. Nginx's modular event-driven architecture can provide predictable performance under high loads. HTTP proxy and Web server features Ability to handle more than 10,000 simultaneous connections with a low memory footprint (~2.5 MB per 10k inactive HTTP keep-alive connections) Handling of static files, index files and auto-indexing Reverse proxy with caching Load balancing[26] with in-band health checks TLS/SSL with SNI and OCSP stapling support, via OpenSSL FastCGI, SCGI, uWSGI support with caching gRPC support since March 2018, version 1.13.10. Name- and IP address-based virtual servers IPv6-compatible WebSockets since 1.3.13,[29] including acting as a reverse proxy and do load balancing of WebSocket applications. HTTP/1.1 Upgrade (101 Switching Protocols) HTTP/2 protocol support HTTP/3 protocol support (experimental since 1.25.0) URL rewriting and redirection Mail proxy features TLS/SSL support STARTTLS support SMTP,[35] POP3, and IMAP proxy Requires authentication using an external HTTP server or by an authentication script Other features include upgrading executable and configuration without client connections loss, and a module-based architecture with both core[38] and third-party module support. The paid Plus product includes additional features such as advanced load balancing and access to an expanded suite of metrics for performance monitoring.