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Real-Time Updates (SSE)

Overview

Flagent supports real-time flag updates via Server-Sent Events (SSE). Clients receive updates when flags change, without polling or restarting the application.

Current implementation: SSE is available in Kotlin Enhanced and Go Enhanced SDKs. WebSocket is planned.

Key features

1. WebSocket support

Bidirectional communication for real-time updates.

Benefits: Low latency, bidirectional, efficient, multiple connections.

Protocol: ws://flags.example.com/ws

Example:

val wsClient = FlagentWebSocketClient(
    url = "wss://flags.example.com/ws",
    apiKey = "your-api-key"
)
wsClient.subscribe("new_payment_flow") { flag ->
    println("Flag updated: ${flag.key} - enabled: ${flag.enabled}")
    localCache.update(flag)
}
wsClient.evaluate(
    flagKey = "new_payment_flow",
    entityID = "user123",
    entityContext = mapOf("country" to "US")
) { result -> println("Evaluation result: ${result.variantKey}") }

2. Server-Sent Events (SSE)

One-way event stream. Benefits: Simple, auto-reconnect, HTTP-based, low overhead.

Endpoint: GET /api/v1/events/stream

Example:

val sseClient = FlagentSSEClient(
    url = "https://flags.example.com/api/v1/events/stream",
    apiKey = "your-api-key"
)
sseClient.subscribe { event ->
    when (event.type) {
        EventType.FLAG_UPDATED -> { val flag = event.data as Flag; localCache.update(flag) }
        EventType.FLAG_DELETED -> { localCache.remove(event.data as String) }
    }
}

3. Subscription management

Subscribe by flag, by tags, to all flags, or to segment changes.

4. Automatic reconnection

Exponential backoff, max attempts, subscription preservation.

5. Event types

FLAG_UPDATED, FLAG_CREATED, FLAG_DELETED, FLAG_ENABLED, FLAG_DISABLED, SEGMENT_UPDATED, DISTRIBUTION_UPDATED.

API

WebSocket: wss://flags.example.com/ws. Message types: subscribe, flag_updated, evaluate, evaluation_result (see SDK docs).

SSE: GET /api/v1/events/stream. Headers: Accept: text/event-stream, Authorization: Bearer {token}. Events: flag_updated, flag_created, flag_deleted.

SDK integration

Kotlin and JavaScript clients: FlagentWebSocketClient, FlagentSSEClient with subscribe / subscribeAll.

Configuration

WebSocketConfig (enabled, port, path, pingInterval, maxConnections). SSEConfig (enabled, path, keepAliveInterval, maxClients). Env: FLAGENT_WS_*, FLAGENT_SSE_*.

Use cases

Real-time flag updates without restart; live configuration; debugging and monitoring.

Roadmap

Phase 1: WebSocket server and client. Phase 2: SSE endpoint and client. Phase 3: Event filtering, batch updates, compression, auth.

Related documentation