cloudflare-durable-objects

secondsky/claude-skillsCloud PlatformsReview advisedSnapshot 9a95f6834e39

Installs: 0

Summary

Cloudflare Durable Objects for stateful coordination and real-time apps. Use for chat, multiplayer games, WebSocket hibernation, or encountering class export, migration, alarm errors.

SKILL.md

Cloudflare Durable Objects

Status: Production Ready ✅ Last Updated: 2025-11-25 Dependencies: cloudflare-worker-base (recommended) Latest Versions: [email protected]+, @cloudflare/[email protected]+ Official Docs: https://developers.cloudflare.com/durable-objects/

What are Durable Objects? • Quick Start • When to Load References • Class Structure • State API • WebSocket Hibernation • Alarms • RPC vs HTTP • Stubs & Routing • Migrations • Common Patterns • Critical Rules • Known Issues

What are Durable Objects?

Globally unique, stateful objects with single-point coordination, strong consistency (ACID), WebSocket Hibernation (thousands of connections), SQLite storage (1GB), and alarms API.

Use for: Chat rooms, multiplayer games, rate limiting, session management, leader election, stateful workflows

Quick Start (10 Minutes)

Option 1: Scaffold New DO Project

npm create cloudflare@latest my-durable-app -- \
  --template=cloudflare/durable-objects-template --ts --git --deploy false
cd my-durable-app && bun install && npm run dev

Option 2: Add to Existing Worker

1. Install types:

bun add -d @cloudflare/workers-types

import { DurableObject } from 'cloudflare:workers';

export class Counter extends DurableObject {
  async increment(): Promise<number> {
    let value: number = (await this.ctx.storage.get('value')) || 0;
    await this.ctx.storage.put('value', ++value);
    return value;
  }
}

export default Counter;  // CRITICAL

{
  "durable_objects": {
    "bindings": [{ "name": "COUNTER", "class_name": "Counter" }]
  },
  "migrations": [
    { "tag": "v1", "new_sqlite_classes": ["Counter"] }
  ]
}

import { Counter } from './counter';

interface Env {
  COUNTER: DurableObjectNamespace<Counter>;
}

export { Counter };

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const stub = env.COUNTER.getByName('global-counter');
    return new Response(`Count: ${await stub.increment()}`);
  },
};

bunx wrangler deploy

import { DurableObject } from 'cloudflare:workers';

export class MyDO extends DurableObject {
  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);  // Required first line
    // Keep minimal - heavy work blocks hibernation
    ctx.blockConcurrencyWhile(async () => {
      // Load from storage before handling requests
    });
  }

  async myMethod(): Promise<string> {  // RPC method (recommended)
    return 'Hello!';
  }
}

export default MyDO;  // CRITICAL: Must export

export class Counter extends DurableObject {
  sql: SqlStorage;

  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);
    this.sql = ctx.storage.sql;
    this.sql.exec('CREATE TABLE IF NOT EXISTS counts (key TEXT PRIMARY KEY, value INTEGER)');
  }

  async increment(): Promise<number> {
    this.sql.exec('INSERT OR REPLACE INTO counts (key, value) VALUES (?, ?)', 'count', 1);
    return this.sql.exec('SELECT value FROM counts WHERE key = ?', 'count').one<{value: number}>().value;
  }
}

export class ChatRoom extends DurableObject {
  sessions: Map<WebSocket, any>;

  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);
    this.sessions = new Map();
    // Restore connections after hibernation
    ctx.getWebSockets().forEach(ws => {
      this.sessions.set(ws, ws.deserializeAttachment());
    });
  }

  async fetch(request: Request): Promise<Response> {
    const pair = new WebSocketPair();
    const [client, server] = Object.values(pair);

    this.ctx.acceptWebSocket(server);  // ← Enables hibernation
    server.serializeAttachment({ userId: 'alice' });  // ← Persists across hibernation
    this.sessions.set(server, { userId: 'alice' });

    return new Response(null, { status: 101, webSocket: client });
  }

  async webSocketMessage(ws: WebSocket, message: string): Promise<void> {
    const session = this.sessions.get(ws);
    // Broadcast to all
    this.sessions.forEach((_, w) => w.send(message));
  }
}

export class Batcher extends DurableObject {
  async addItem(item: string): Promise<void> {
    await this.ctx.storage.put('items', [...existingItems, item]);

    // Schedule batch processing if not already scheduled
    if (await this.ctx.storage.getAlarm() === null) {
      await this.ctx.storage.setAlarm(Date.now() + 10000);  // 10 seconds
    }
  }

  async alarm(info: { retryCount: number; isRetry: boolean }): Promise<void> {
    const items = await this.ctx.storage.get('items');
    await this.processBatch(items);  // Send to API, write to DB, etc.
    await this.ctx.storage.put('items', []);  // Clear buffer
  }
}

// RPC Pattern (simpler)
export class Counter extends DurableObject {
  async increment(): Promise<number> {  // ← Direct method
    let value = await this.ctx.storage.get<number>('count') || 0;
    return ++value;
  }
}
const count = await stub.increment();  // ← Direct call

// HTTP Fetch Pattern
export class Counter extends DurableObject {
  async fetch(request: Request): Promise<Response> {  // ← HTTP handler
    const url = new URL(request.url);
    if (url.pathname === '/increment') { /* ... */ }
  }
}
const response = await stub.fetch('/increment', { method: 'POST' });

// Method 1: From ID
const id = env.CHAT_ROOM.idFromName('room-123');
const stub = env.CHAT_ROOM.get(id);

// Method 2: Shortcut for named DOs (recommended)
const stub = env.CHAT_ROOM.getByName('room-123');

await stub.myMethod();

{
  "durable_objects": {
    "bindings": [{ "name": "COUNTER", "class_name": "Counter" }]
  },
  "migrations": [
    {
      "tag": "v1",                    // Unique identifier (append-only)
      "new_sqlite_classes": ["Counter"]
    }
  ]
}

export class RateLimiter extends DurableObject {
  async checkLimit(userId: string, limit: number, window: number): Promise<boolean> {
    const requests = await this.ctx.storage.get<number[]>(`rate:${userId}`) || [];
    const validRequests = requests.filter(t => Date.now() - t < window);

    if (validRequests.length >= limit) return false;

    validRequests.push(Date.now());
    await this.ctx.storage.put(`rate:${userId}`, validRequests);
    return true;
  }
}

cloudflare-durable-objects

Summary

SKILL.md

Cloudflare Durable Objects

Table of Contents

What are Durable Objects?

Use for: Chat rooms, multiplayer games, rate limiting, session management, leader election, stateful workflows

Quick Start (10 Minutes)

Option 1: Scaffold New DO Project

Option 2: Add to Existing Worker

Available Commands

Autonomous Agents

When to Load References

Durable Object Class Structure

State API - Persistent Storage

WebSocket Hibernation API

Alarms API - Scheduled Tasks

RPC vs HTTP Fetch

Creating Durable Object Stubs and Routing

Migrations - Managing DO Classes

Common Patterns

Critical Rules

Known Issues Prevention

Issue #1: Class Not Exported

Issue #2: Missing Migration

Issue #3: setTimeout Breaks Hibernation

Configuration & TypeScript

Related skills