Users' Manual
Version 1.9 — Rev. 3

# Introduction

OpenLiteSpeed (OLS) is a high-performance, open-source web server. It serves as a free alternative to LiteSpeed Web Server Enterprise and provides compatibility with Apache rewrite rules.

OLS uses an event-driven architecture and includes a built-in caching engine (LSCache).

## Overview

OpenLiteSpeed supports modern protocols including HTTP/2 and HTTP/3 (QUIC). It is suitable for standalone servers, development environments, and production use, particularly for individual sites or environments that prefer an open-source solution under the GPLv3 license.

## Features

### Protocols and compatibility

- HTTP/1.0, HTTP/1.1, HTTP/2, and HTTP/3 (QUIC)
- GZIP and Brotli compression
- WebSocket proxying
- IPv4 and IPv6 support
- Unlimited IP-based and name-based virtual hosting
- HTTPS with OCSP stapling
- Support for PHP, Perl, Ruby, Python, and other scripting languages via LSAPI, CGI, FastCGI, and other interfaces

### Performance and scalability

- Event-driven architecture
- Low memory usage
- High concurrent connection capacity
- `sendfile()` and asynchronous I/O
- LiteSpeed Server Application Programming Interface (LSAPI) for dynamic content
- Built-in LSCache for dynamic page caching
- `.htaccess` rewrite rule support (requires restart to apply changes)

### Apache compatibility

- Support for Apache mod_rewrite rules
- Compatible with many common Apache rewrite configurations

### Security

- Connection and bandwidth throttling
- mod_security v3 compatibility
- Protection against common SSL attacks
- Strict HTTP request validation and buffer overrun prevention
- suEXEC support
- Chroot support

### Management

- WebAdmin Console for configuration and real-time monitoring
- Virtual host templates
- Support for multiple PHP versions
- Real-time statistics
- LiteSpeed Prometheus Exporter

### Additional features

- MP4/FLV streaming
- Geo-IP lookup
- Custom logging