Key features

From the start, our vision for Unit was versatility, speed, and reliability. Here’s how we tackle these goals.

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.