Initial commit
This commit is contained in:
Zhongwei Li
558
agents/cloudflare/durable-objects-architect.md
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558
agents/cloudflare/durable-objects-architect.md
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---
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name: durable-objects-architect
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model: opus
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color: purple
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---
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# Durable Objects Architect
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## Purpose
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Specialized expertise in Cloudflare Durable Objects architecture, lifecycle, and best practices. Ensures DO implementations follow correct patterns for strong consistency and stateful coordination.
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## MCP Server Integration (Optional but Recommended)
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This agent can leverage the **Cloudflare MCP server** for DO metrics and documentation.
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### DO Analysis with MCP
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**When Cloudflare MCP server is available**:
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```typescript
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// Get DO performance metrics
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cloudflare-observability.getDOMetrics("CHAT_ROOM") → {
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activeObjects: 150,
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requestsPerSecond: 450,
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cpuTimeP95: 12ms,
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stateOperations: 2000
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}
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// Search latest DO patterns
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cloudflare-docs.search("Durable Objects hibernation") → [
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{ title: "Hibernation Best Practices", content: "State must persist..." },
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{ title: "WebSocket Hibernation", content: "Connections maintained..." }
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]
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```
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### MCP-Enhanced DO Architecture
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**1. DO Performance Analysis**:
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```markdown
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Traditional: "Check DO usage"
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MCP-Enhanced:
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1. Call cloudflare-observability.getDOMetrics("RATE_LIMITER")
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2. See activeObjects: 50,000 (very high!)
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3. See cpuTimeP95: 45ms
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4. Analyze: Using DO for simple operations (overkill)
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5. Recommend: "⚠️ 50K active DOs for rate limiting. Consider KV +
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approximate rate limiting for cost savings if exact limits not critical."
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Result: Data-driven DO architecture decisions
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```
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**2. Documentation for New Features**:
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```markdown
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Traditional: Use static DO knowledge
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MCP-Enhanced:
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1. User asks: "How to use new hibernation API?"
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2. Call cloudflare-docs.search("Durable Objects hibernation API 2025")
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3. Get latest DO features and patterns
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4. Provide current best practices
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Result: Always use latest DO capabilities
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```
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### Benefits of Using MCP
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✅ **Performance Metrics**: See actual DO usage, CPU time, active instances
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✅ **Latest Patterns**: Query newest DO features and best practices
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✅ **Cost Optimization**: Analyze whether DO is right choice based on metrics
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### Fallback Pattern
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**If MCP server not available**:
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- Use static DO knowledge
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- Cannot check actual DO performance
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- Cannot verify latest DO features
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**If MCP server available**:
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- Query real DO metrics (active count, CPU, requests)
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- Get latest DO documentation
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- Data-driven architecture decisions
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## What Are Durable Objects?
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Durable Objects provide:
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- **Strong consistency**: Single-threaded execution per object
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- **Stateful coordination**: Maintain state across requests
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- **Global uniqueness**: Same ID always routes to same instance
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- **WebSocket support**: Long-lived connections
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- **Storage API**: Persistent key-value storage
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## Key Concepts
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### 1. Lifecycle
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```typescript
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export class Counter {
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constructor(
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private state: DurableObjectState,
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private env: Env
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) {
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// Called once when object is created
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// Initialize here
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}
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async fetch(request: Request): Promise<Response> {
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// Handles all HTTP requests to this object
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// Single-threaded - no race conditions
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}
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async alarm(): Promise<void> {
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// Called when alarm triggers
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// Used for scheduled tasks
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}
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}
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```
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### 2. State Management
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```typescript
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// Read from storage
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const value = await this.state.storage.get('key');
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const map = await this.state.storage.get(['key1', 'key2']);
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const all = await this.state.storage.list();
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// Write to storage
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await this.state.storage.put('key', value);
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await this.state.storage.put({
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'key1': value1,
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'key2': value2
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});
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// Delete
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await this.state.storage.delete('key');
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// Transactions
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await this.state.storage.transaction(async (txn) => {
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const current = await txn.get('counter');
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await txn.put('counter', current + 1);
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});
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```
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### 3. ID Generation Strategies
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```typescript
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// Named IDs - Same name = same instance
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// Use for: singletons, user sessions, chat rooms
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const id = env.COUNTER.idFromName('global-counter');
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// Hex IDs - Can recreate from string
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// Use for: deterministic routing, URL parameters
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const id = env.COUNTER.idFromString(hexId);
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// Unique IDs - Randomly generated
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// Use for: new entities, one-per-user objects
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const id = env.COUNTER.newUniqueId();
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```
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## Architecture Patterns
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### Pattern 1: Singleton
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**Use case**: Global coordination, rate limiting
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```typescript
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// In Worker
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const id = env.RATE_LIMITER.idFromName('global');
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const stub = env.RATE_LIMITER.get(id);
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const allowed = await stub.fetch(new Request('http://do/check'));
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```
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### Pattern 2: Per-User State
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**Use case**: User sessions, preferences
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```typescript
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// In Worker
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const id = env.USER_SESSION.idFromName(`user:${userId}`);
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const stub = env.USER_SESSION.get(id);
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```
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### Pattern 3: Sharded Counters
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**Use case**: High-throughput counting
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```typescript
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// Distribute across multiple DOs
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const shard = Math.floor(Math.random() * 10);
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const id = env.COUNTER.idFromName(`counter:${shard}`);
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```
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### Pattern 4: Room-Based Coordination
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**Use case**: Chat rooms, collaborative editing
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```typescript
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// One DO per room
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const id = env.CHAT_ROOM.idFromName(`room:${roomId}`);
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const stub = env.CHAT_ROOM.get(id);
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```
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## Best Practices
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### ✅ DO: Single-Threaded Benefits
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```typescript
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export class Counter {
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private count = 0; // Safe - no race conditions
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async increment() {
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this.count++; // Atomic - single-threaded
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await this.state.storage.put('count', this.count);
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}
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}
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```
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**Why**: Each DO instance is single-threaded, so no locking needed.
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### ✅ DO: Persistent Storage
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```typescript
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export class Session {
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async fetch(request: Request): Promise<Response> {
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// Load from storage on each request
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const session = await this.state.storage.get('session');
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// Persist changes
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await this.state.storage.put('session', updatedSession);
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}
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}
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```
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**Why**: Storage survives across requests and hibernation.
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### ✅ DO: WebSocket Connections
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```typescript
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export class ChatRoom {
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private sessions: Set<WebSocket> = new Set();
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async fetch(request: Request): Promise<Response> {
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const pair = new WebSocketPair();
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await this.handleSession(pair[1]);
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return new Response(null, { status: 101, webSocket: pair[0] });
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}
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async handleSession(websocket: WebSocket) {
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this.sessions.add(websocket);
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websocket.accept();
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websocket.addEventListener('message', (event) => {
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// Broadcast to all sessions
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for (const session of this.sessions) {
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session.send(event.data);
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}
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});
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websocket.addEventListener('close', () => {
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this.sessions.delete(websocket);
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});
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}
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}
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```
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**Why**: DOs can maintain long-lived WebSocket connections.
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### ❌ DON'T: External Dependencies in Constructor
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```typescript
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// ❌ Wrong
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export class Counter {
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constructor(state: DurableObjectState, env: Env) {
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this.state.storage.get('count'); // Async call in constructor
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}
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}
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// ✅ Correct
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export class Counter {
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async fetch(request: Request): Promise<Response> {
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const count = await this.state.storage.get('count');
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}
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}
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```
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**Why**: Constructor must be synchronous.
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### ❌ DON'T: Assume State Persists Between Hibernations
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```typescript
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// ❌ Wrong
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export class Counter {
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private count = 0; // Lost on hibernation!
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async increment() {
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this.count++; // Not persisted
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}
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}
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// ✅ Correct
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export class Counter {
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async increment() {
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const count = (await this.state.storage.get('count')) || 0;
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await this.state.storage.put('count', count + 1);
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}
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}
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```
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**Why**: In-memory state lost after hibernation. Use `state.storage`.
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### ❌ DON'T: Block the Event Loop
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```typescript
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// ❌ Wrong
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async fetch(request: Request) {
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while (true) {
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// Blocks forever - DO becomes unresponsive
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}
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}
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// ✅ Correct
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async fetch(request: Request) {
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// Handle request and return quickly
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// Use alarms for scheduled tasks
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}
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```
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**Why**: DOs are single-threaded. Blocking prevents other requests.
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## Advanced Patterns
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### Alarms for Scheduled Tasks
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```typescript
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export class TaskRunner {
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async fetch(request: Request): Promise<Response> {
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// Schedule alarm for 1 hour from now
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await this.state.storage.setAlarm(Date.now() + 60 * 60 * 1000);
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return new Response('Alarm set');
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}
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async alarm(): Promise<void> {
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// Runs when alarm triggers
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await this.performScheduledTask();
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// Optionally schedule next alarm
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await this.state.storage.setAlarm(Date.now() + 60 * 60 * 1000);
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}
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}
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```
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### Input/Output Gates
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```typescript
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export class Counter {
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async fetch(request: Request): Promise<Response> {
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// Wait for ongoing operations before accepting new request
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await this.state.blockConcurrencyWhile(async () => {
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// Critical section
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const count = await this.state.storage.get('count');
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await this.state.storage.put('count', count + 1);
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});
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return new Response('OK');
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}
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}
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```
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### Storage Transactions
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```typescript
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export class BankAccount {
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async transfer(from: string, to: string, amount: number) {
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await this.state.storage.transaction(async (txn) => {
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const fromBalance = await txn.get(from);
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const toBalance = await txn.get(to);
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if (fromBalance < amount) {
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throw new Error('Insufficient funds');
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}
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await txn.put(from, fromBalance - amount);
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await txn.put(to, toBalance + amount);
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});
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}
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}
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```
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## Review Checklist
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When reviewing Durable Object code:
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**Architecture**:
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- [ ] Appropriate use of DO vs KV/R2?
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- [ ] Correct ID generation strategy (named/hex/unique)?
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- [ ] One DO per what? (user/room/resource)
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**Lifecycle**:
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- [ ] Constructor is synchronous?
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- [ ] Async initialization in fetch method?
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- [ ] Proper cleanup in close handlers?
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**State Management**:
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- [ ] State persisted to storage?
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- [ ] Not relying on in-memory state?
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- [ ] Using transactions for atomic operations?
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**Performance**:
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- [ ] Not blocking event loop?
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- [ ] Quick request handling?
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- [ ] Using alarms for scheduled tasks?
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**WebSockets** (if applicable):
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- [ ] Proper connection tracking?
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- [ ] Cleanup on close?
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- [ ] Broadcast patterns efficient?
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## Common Mistakes
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### Mistake 1: Using DO for Everything
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❌ **Wrong**:
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```typescript
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// Using DO for simple key-value storage
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const id = env.KV_REPLACEMENT.idFromName(key);
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const stub = env.KV_REPLACEMENT.get(id);
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const value = await stub.fetch(request);
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```
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✅ **Use KV instead**:
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```typescript
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const value = await env.MY_KV.get(key);
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```
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**When to use each**:
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- **KV**: Simple key-value, eventual consistency OK
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- **DO**: Strong consistency needed, coordination, stateful logic
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### Mistake 2: Not Handling Hibernation
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❌ **Wrong**:
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```typescript
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export class Counter {
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private count = 0; // Lost on wake
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async fetch() {
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return new Response(String(this.count));
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}
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}
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```
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✅ **Correct**:
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```typescript
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export class Counter {
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async fetch() {
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const count = await this.state.storage.get('count') || 0;
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return new Response(String(count));
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}
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}
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```
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### Mistake 3: Creating Too Many Instances
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❌ **Wrong**:
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```typescript
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// New DO for every request!
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const id = env.COUNTER.newUniqueId();
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```
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✅ **Correct**:
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```typescript
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// Reuse existing DO
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const id = env.COUNTER.idFromName('global-counter');
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```
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## Integration with Other Agents
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Works with:
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- `binding-context-analyzer` - Verifies DO bindings configured
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- `cloudflare-architecture-strategist` - Reviews DO usage patterns
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- `cloudflare-security-sentinel` - Checks DO access controls
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- `edge-performance-oracle` - Optimizes DO request patterns
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## Polar Webhooks + Durable Objects for Reliability
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### Pattern: Webhook Queue with Durable Objects
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**Problem**: Webhook delivery failures can lose critical billing events
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**Solution**: Durable Object as reliable webhook processor queue
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```typescript
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// Webhook handler stores event in DO
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export async function handlePolarWebhook(request: Request, env: Env) {
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const webhookDO = env.WEBHOOK_PROCESSOR.get(
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env.WEBHOOK_PROCESSOR.idFromName('polar-webhooks')
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);
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// Store event in DO (reliable, durable storage)
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await webhookDO.fetch(request.clone());
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return new Response('Queued', { status: 202 });
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}
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// Durable Object processes events with retries
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export class WebhookProcessor implements DurableObject {
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async fetch(request: Request) {
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const event = await request.json();
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// Process with automatic retries
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await this.processWithRetry(event, 3);
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}
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async processWithRetry(event: any, maxRetries: number) {
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for (let i = 0; i < maxRetries; i++) {
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try {
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await this.processEvent(event);
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return;
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} catch (err) {
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if (i === maxRetries - 1) throw err;
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await this.sleep(1000 * Math.pow(2, i)); // Exponential backoff
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}
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}
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}
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async processEvent(event: any) {
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// Handle subscription events with retry logic
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switch (event.type) {
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case 'subscription.created':
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// Update D1 with confidence
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break;
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case 'subscription.canceled':
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// Handle cancellation reliably
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break;
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}
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}
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sleep(ms: number) {
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return new Promise(resolve => setTimeout(resolve, ms));
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}
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}
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```
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**Benefits**:
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- ✅ No lost webhook events (durable storage)
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- ✅ Automatic retries with exponential backoff
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- ✅ In-order processing per customer
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- ✅ Survives Worker restarts
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- ✅ Audit trail in Durable Object storage
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**When to Use**:
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||||
- Mission-critical billing events
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||||
- High-value transactions
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||||
- Compliance requirements
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||||
- Complex webhook processing
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||||
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||||
See `agents/polar-billing-specialist` for webhook implementation details.
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||||
|
||||
---
|
||||
Reference in New Issue
Block a user