Edge Computing with Cloudflare Workers & Deno · レッスン

Durable Objectsの概要

ステートフルなサーバーレスアプリケーション向けのDurable Objectsを理解し、グローバルに一貫した状態を維持します

「Durable Objectsの概要」はCoddyKit上の無料Edge Computing with Cloudflare Workers & Denoレッスンです。これはレッスン2/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはEdge Computing with Cloudflare Workers & Deno学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Edge Computing with Cloudflare Workers & Denoコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

The State Problem at the Edge

Serverless functions, like Cloudflare Workers, are typically stateless. This means each request is processed independently, without remembering past interactions.

While great for scalability and cost-efficiency, what if you need to maintain a consistent piece of information across multiple requests or users globally? Think about a live chat room, a game lobby, or a shared counter.

Introducing Durable Objects

Cloudflare Durable Objects solve this fundamental challenge. They are a powerful primitive for building stateful serverless applications directly at the edge.

They provide a single-instance, globally consistent object.
Each Durable Object instance has a unique ID and its own private storage.
They act like tiny, persistent servers that live at the edge.

Unique IDs & Global Consistency

The core concept behind Durable Objects is their unique identity. When you create or retrieve a Durable Object using a specific ID, Cloudflare ensures that only one instance of that object exists and runs globally.

No matter where a request originates from (e.g., Tokyo, New York, London), if it targets the same Durable Object ID, it will be routed to that single, consistent instance. This eliminates the need for complex distributed synchronization.

Anatomy of a Durable Object

A Durable Object is defined as a standard JavaScript class. It must have:

A constructor(state, env) method, where state provides access to its storage and env holds environment variables.
An async fetch(request) method, which processes incoming HTTP requests, similar to a regular Worker.

It's essentially a self-contained, stateful mini-Worker.

Persistent Storage with state.storage

Each Durable Object instance has its own private, durable key-value storage, accessible via this.state.storage. This allows the object to persist data across invocations and even across restarts.

await this.state.storage.put('key', value): Stores data.
await this.state.storage.get('key'): Retrieves data.
await this.state.storage.delete('key'): Removes data.

Values can be any JSON-serializable type, making it versatile for various data needs.

Code: Counter Worker & DO

This example shows a Cloudflare Worker interacting with a simple Counter Durable Object. The DO maintains a count that persists across requests and is globally consistent.

To run this, you'd define the Counter Durable Object binding in your wrangler.toml file.

export class Counter {
  constructor(state, env) {
    this.state = state;
    this.env = env;
  }

  async fetch(request) {
    let url = new URL(request.url);
    // Retrieve current count from storage, default to 0
    let currentCount = (await this.state.storage.get("value")) || 0;

    if (url.pathname === "/increment") {
      currentCount++;
      await this.state.storage.put("value", currentCount);
      return new Response(`Count: ${currentCount}`);
    } else if (url.pathname === "/decrement") {
      currentCount--;
      await this.state.storage.put("value", currentCount);
      return new Response(`Count: ${currentCount}`);
    } else if (url.pathname === "/get") {
      return new Response(`Count: ${currentCount}`);
    }

    return new Response("Not found", { status: 404 });
  }
}

export default {
  async fetch(request, env) {
    // Get a unique Durable Object ID based on a name
    // 'COUNTER' is the binding name configured in wrangler.toml
    let id = env.COUNTER.idFromName("global-counter");
    // Get a 'stub' (a proxy) to interact with the Durable Object
    let stub = env.COUNTER.get(id);

    // Forward the incoming request to the Durable Object's fetch method
    return stub.fetch(request);
  }
};

How the Counter Code Works

1. The Counter class defines the Durable Object's behavior, handling /increment, /decrement, and /get routes and persisting its value.

2. The main Worker's fetch handler:

It uses env.COUNTER.idFromName("global-counter") to obtain a deterministic ID for our counter.
env.COUNTER.get(id) returns a stub, which is a network proxy to the Durable Object.
stub.fetch(request) forwards the original request to the Durable Object instance, allowing it to process the request and update its state.

Global Consistency in Action

Imagine users from different locations (e.g., Europe, Asia, Americas) all interacting with the /increment endpoint of your Worker. Because they all target the "global-counter" ID, Cloudflare guarantees they will all interact with the exact same instance of the Counter Durable Object.

This ensures that the count is always consistent, regardless of the user's location, simplifying complex distributed state management that would otherwise be very challenging.

Common Use Cases for DOs

Durable Objects are ideal for scenarios requiring strong consistency and shared, mutable state at the edge:

Real-time Collaboration: Shared whiteboards, document editing.
Gaming: Game lobbies, player state, matchmaking.
Live Chat: Chat rooms, message queues for real-time communication.
Stateful APIs: Managing user sessions, shopping carts, or unique resource locks.

They bring traditional stateful patterns to the serverless edge, making complex applications simpler to build.

Quick Check: Durable Objects

Which of the following best describes the primary benefit of Cloudflare Durable Objects?

Recap: Durable Objects Explained

In this lesson, we explored Cloudflare Durable Objects, a powerful tool for stateful serverless applications.

They provide globally consistent, single-instance state at the edge.
Each DO has a unique ID and private, durable storage (state.storage).
Workers interact with DOs by obtaining stubs and forwarding requests.
They are ideal for real-time, collaborative, and stateful applications that demand strong consistency.

Durable Objects bridge the gap between stateless serverless and traditional stateful services, simplifying complex distributed systems.

よくある質問

「Durable Objectsの概要」レッスンは無料ですか？

はい。「Durable Objectsの概要」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Edge Computing with Cloudflare Workers & Denoコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Edge Computing with Cloudflare Workers & Denoコースには全4レッスンが含まれています。

「Durable Objectsの概要」で何を学びますか？

ステートフルなサーバーレスアプリケーション向けのDurable Objectsを理解し、グローバルに一貫した状態を維持しますブラウザで直接実行するハンズオンコードでEdge Computing with Cloudflare Workers & Denoを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Edge Computing with Cloudflare Workers & Denoを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのEdge Computing with Cloudflare Workers & Denoは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン2/4です。

「Durable Objectsの概要」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このEdge Computing with Cloudflare Workers & Denoレッスンでコードを書いて実行できますか？

はい。すべてのEdge Computing with Cloudflare Workers & Denoレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

このコースのすべてのレッスン

← Edge Computing with Cloudflare Workers & Denoに戻る