ADR 4: Event Model — REST Watch and SSE

Status: Accepted

Context

RezusCloud needs real-time event delivery for boot progress, state changes, and dashboard updates. The original design used NATS as an event bus, but the REST API already provides a watch endpoint for state changes. NATS became redundant.

Decision

Remove NATS entirely. Events use REST-based mechanisms:

Boot Progress (CLI → stdout)

Boot progress is printed to stdout during rezusctl boot. No event bus needed — the CLI is attached to the terminal for the duration of boot.

API Events (Watch + SSE)

The REST API provides watch endpoints for real-time state updates:

• GET /api/v1/tenants?watch=true — chunked JSON streaming for CLI
• GET /api/v1/tenants?watch=true&sse=true — Server-Sent Events for WebUI
• GET /api/v1/tenants/{c}/machines/{id}/logs — SSE machine log streaming

The event bus (internal/watch/) publishes resource change events. Subscribers receive them via the watch API.

Real-Time WebUI Updates

The WebUI subscribes to SSE streams from the REST API. HTMX + Alpine.js process events and update the UI.

Consequences

• One fewer infrastructure dependency. No NATS server, no NATS client library.
• Events are accessible to all API clients (CLI, WebUI, programmatic).
• The internal/watch/ package provides the event bus with WatchableStore wrapper.
• Boot progress remains stdout-only.