Flexibility§

• The entire configuration is managed dynamically over HTTP via a friendly RESTful JSON API.

• Updates to the configuration are performed granularly at runtime with zero interruption.

• Requests are routed between static content, upstream servers, and local apps.

• Request filtering and dispatching uses elaborate matching rules that enable regular expressions, response header awareness, and njs scripting.

• Apps in multiple languages and language versions run side by side.

• Server-side WebAssembly is natively supported.

• Common language-specific APIs for all supported languages run seamlessly.

• Upstream server groups provide dynamic load balancing using a weighted round-robin method.

• Originating IP identification supports X-Forwarded-For and similar header fields.

Performance§

• Requests are asynchronously processed in threads with efficient event loops (epoll, kqueue).

• Syscalls and data copy operations are kept to a necessary minimum.

• 10,000 inactive HTTP keep-alive connections take up only a few MBs of memory.

• Router and app processes rely on low-latency IPC built with lock-free queues over shared memory.

• Built-in statistics provide insights into Unit’s performance.

• The number of per-app processes is defined statically or scales preemptively within given limits.

• App and instance usage statistics are collected and exposed via the API.

• Multithreaded request processing is supported for Java, Perl, Python, and Ruby apps.

Security & Robustness§

• Client connections are handled by a separate non-privileged router process.

• Low-resource conditions (out of memory or descriptors) and app crashes are handled gracefully.

• SSL/TLS with SNI, session cache and tickets is integrated (OpenSSL 1.0.1 and later).

• Different apps are isolated in separate processes.

• Apps can be additionally containerized with namespace and file system isolation.

• Static file serving benefits from chrooting, symlink and mount point traversal restrictions.

Supported App Languages§

Unit interoperates with:

• Binary-compiled languages in general: using the embedded libunit library.

• Go: by overriding the http module.

• JavaScript (Node.js): by automatically overloading the http and websocket modules.

• Java: by using the Servlet Specification 3.1 and WebSocket APIs.

• Perl: by using PSGI.

• PHP: by using a custom SAPI module.

• Python: by using WSGI or ASGI with WebSocket support.

• Ruby: by using the Rack API.

• WebAssembly: by using Wasmtime.