Prosody IM

Prosody is a lightweight yet fully‑featured XMPP (Jabber) server written in Lua. It implements the core XMPP RFCs while providing a modular architecture that lets developers plug in new features or prototype custom protocols with minimal effort. At its heart, Prosody exposes a simple XML‑stream based API that clients and other servers use for real‑time messaging, presence, and group chat. The server’s event loop is single‑threaded but highly efficient, making it suitable for both small home deployments and larger multi‑tenant setups.

Key Features & Core Capabilities

• Modular plugin system – Every feature (MUC, vCard, roster management, SASL authentication) is a Lua module that can be enabled or disabled in prosody.cfg.lua. Plugins can expose their own REST‑like APIs, WebSocket endpoints, or XMPP extensions (XEPs) for developers to build upon.
• Extensible authentication – Supports a variety of SASL mechanisms out of the box and allows custom auth back‑ends (SQL, LDAP, external services) through Lua scripts.
• Multi‑domain support – Prosody can host thousands of virtual hosts, each with its own configuration, enabling multi‑tenant SaaS deployments or isolated departmental servers.
• Built‑in federation – By default it can act as a gateway to any XMPP server, handling routing, offline messages, and stream management per RFC 6120/6121.

Technical Stack & Architecture

Prosody’s architecture is intentionally minimalistic: the core handles stream negotiation, routing, and authentication; everything else lives in plugins. This separation keeps memory usage low (≈10 MB on a typical server) and simplifies debugging because each plugin can be isolated.

Deployment & Infrastructure

Prosody is designed for self‑hosting, but it integrates seamlessly with modern DevOps tooling:

• Containerization – Official Docker images expose a single prosody.cfg.lua volume for configuration and a data volume for persistence. Kubernetes manifests are available in the community repo.
• Scalability – While single‑process, Prosody can be horizontally scaled by running multiple instances behind a load balancer and using shared storage (e.g., PostgreSQL) for session state. The event‑driven nature also makes it efficient on low‑cost VPS or even Raspberry Pi hardware.
• Resource footprint – On a typical 1 GHz CPU and 512 MB RAM, Prosody can handle several thousand concurrent connections with minimal latency.

Integration & Extensibility

Prosody exposes a rich set of APIs for developers:

• Lua API – Direct access to the server’s internals, allowing custom message routing, presence filtering, or even new XMPP extensions.
• HTTP endpoints – Via the prosody-http plugin, developers can create RESTful services that interact with XMPP (e.g., webhook triggers for incoming messages).
• Webhooks & Callbacks – Plugins can register callbacks on events such as message, presence, or iq to integrate with external systems (CRM, monitoring dashboards).

The plugin ecosystem is mature; popular modules include mod_mam for message archive management, mod_pubsub for XMPP pub/sub, and third‑party auth plugins that connect to OAuth2 or OpenID Connect providers.

Developer Experience

Prosody’s configuration language (prosody.cfg.lua) is Lua‑based, making it both expressive and familiar to developers who already use Lua. The documentation is comprehensive, with a dedicated developer section that explains the plugin API and core hooks. Community support is strong: mailing lists, IRC channels, and a GitHub issue tracker provide quick assistance. The permissive MIT/X11 license removes licensing concerns, allowing commercial use without copyleft obligations.

Use Cases

• Enterprise chat – Deploy a private XMPP server for internal communication, integrating with LDAP for user provisioning.
• IoT messaging – Use XMPP’s lightweight streams to send telemetry from devices, leveraging Prosody’s low memory footprint.
• SaaS communication layer – Host multiple virtual hosts for different customers, each isolated yet sharing a common codebase.
• Experimental protocol prototyping – Rapidly add new XMPP extensions via Lua plugins to test emerging standards.

Advantages Over Alternatives

Prosody’s combination of low overhead, Lua‑