unitd

Unitd is the core daemon of NGINX Unit, a dynamic application server designed to run web applications and services in multiple programming languages under a single process model. The unitd process manages worker processes, loads language runtimes as modules, and coordinates communication between listening sockets, application code, and the administrative API. It is designed to support on-the-fly reconfiguration, allowing changes to the deployed applications and routes without restarting the daemon.

Configuration is defined and modified via a RESTful API exposed by unitd or via the unitctl CLI tool. Configurations describe listening sockets, routing rules, and one or more applications, each with a type (language runtime), a path to the application code, and optional runtime settings. The system is designed to isolate applications for security and resource control.

Runtimes: Unit supports multiple languages through dedicated runtimes such as Node.js, Python, PHP, Ruby, Perl, and Go. Applications can be added, updated, or removed at runtime.

Deployment and usage: After installing, unitd runs as a background service. Admin actions are performed via unitctl or HTTP REST calls to the admin interface; unitd can be configured to run behind a web server or directly handle traffic depending on configuration. The design emphasizes easy hot reconfiguration and small memory footprint.

History and development: Created by NGINX, Unit was developed to provide a flexible, multi-language application server with dynamic reloading and centralized management, aiming to simplify deploying and updating modern web applications.