Edge Computing with Cloudflare Workers & Deno · 课时

使用 Deno 构建数据库代理

使用 Deno 和 Workers 创建高效的数据库代理，连接传统数据库或无服务器数据库

使用 Deno 构建数据库代理 是 CoddyKit 上的免费 Edge Computing with Cloudflare Workers & Deno 课时。这是第 3 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Edge Computing with Cloudflare Workers & Deno 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Edge Computing with Cloudflare Workers & Deno 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

What are Database Proxies?

Welcome to our lesson on Deno database proxies! An edge database proxy acts as an intermediary layer between your application (like a Cloudflare Worker) and your database.

Instead of your edge function connecting directly to the database, it talks to the proxy. The proxy then handles the actual database connection.

Why use them? They centralize connection management, enhance security, and enable data transformation before reaching your database.

Why Deno for Proxies?

Deno is an excellent choice for building these database proxies at the edge. Here's why:

Native HTTP Server: Deno has a powerful, built-in web server, perfect for handling proxy requests.
Security Model: Its granular permission system means you explicitly grant network or file access, enhancing security.
Performance: Deno's fast startup times and efficient runtime make it suitable for responsive proxy services.
TypeScript First: Built-in TypeScript support helps you write more robust and maintainable code for your proxy logic.

Your First Deno Proxy Server

Let's start by creating a basic Deno HTTP server. This server will listen for incoming requests and respond with a simple message, acting as the foundation for our proxy.

Try running this example:

Deno.serve(async (req) => {
  const url = new URL(req.url);
  if (url.pathname === "/") {
    return new Response("Deno Proxy is running!", { status: 200 });
  }
  return new Response("Not Found", { status: 404 });
}, { port: 8000 });

console.log("Deno proxy listening on http://localhost:8000");

Forwarding Requests to DB

Now, let's modify our Deno proxy to forward incoming requests to a 'mock' database endpoint. In a real scenario, this would be your actual database API or a service that interacts with it.

Here, we use a public JSONPlaceholder API to simulate a database call.

Deno.serve(async (req) => {
  // Mock database endpoint (e.g., a public API)
  const mockDbApi = "https://jsonplaceholder.typicode.com/posts";
  const url = new URL(req.url);

  // Construct the target URL for the actual database call
  let targetUrl = mockDbApi;
  if (url.pathname !== "/") {
    targetUrl += url.pathname; // Append path for specific resources
  }

  const proxyReq = new Request(targetUrl, {
    method: req.method,
    headers: req.headers, // Pass original headers
    body: req.body,       // Pass original body
  });

  try {
    const dbResponse = await fetch(proxyReq);
    // Add a custom header to indicate proxy processing
    const newResponse = new Response(dbResponse.body, dbResponse);
    newResponse.headers.set("X-Proxy-By", "Deno");
    return newResponse;
  } catch (error) {
    return new Response(`Proxy Error: ${error.message}`, { status: 500 });
  }
}, { port: 8000 });

console.log("Deno proxy forwarding on http://localhost:8000");

The Need for Connection Pooling

Database connections are expensive to establish. Serverless functions, like Cloudflare Workers, are often short-lived and stateless. If each Worker instance opens a new connection, you can quickly exhaust database connection limits.

Connection pooling is a technique where a pool of open, reusable database connections is maintained. When a request comes in, a connection is borrowed from the pool instead of creating a new one.

Proxy's Role in Pooling

A Deno database proxy can effectively manage connection pooling. Unlike ephemeral Workers, a Deno proxy (e.g., deployed on Deno Deploy or a persistent server) can be a long-lived process.

This allows it to maintain and manage a pool of database connections, serving multiple requests from various Workers without constantly opening and closing connections. This significantly reduces overhead and improves database performance and stability.

Secure Your Database Proxy

Security is paramount. Your Deno proxy acts as a gateway to your database, so it must be secured:

Hide Credentials: Never expose raw database credentials in your Worker code. The proxy should store and use these securely.
Authentication for Proxy: Implement authentication (e.g., API keys, JWTs) for your Workers to access the proxy itself. This ensures only authorized edge functions can send requests.
Permissions: Deno's explicit permission model helps. Only grant the proxy network access to your database, not arbitrary internet access.

Transforming Data at the Edge

Beyond just forwarding, a Deno proxy can transform data. This means modifying request bodies before sending them to the database or altering responses before returning them to the Worker.

This is useful for adding metadata, filtering sensitive information, or normalizing data formats.

Deno.serve(async (req) => {
  const mockDbApi = "https://jsonplaceholder.typicode.com/posts";
  const url = new URL(req.url);
  let targetUrl = mockDbApi;

  // Only transform POST requests for simplicity
  if (req.method === "POST") {
    let requestBody = await req.json(); // Assuming JSON body
    requestBody.processedAt = new Date().toISOString(); // Add a timestamp
    requestBody.source = "edge-proxy"; // Add a source identifier

    const proxyReq = new Request(targetUrl, {
      method: req.method,
      headers: {
        ...req.headers,
        "Content-Type": "application/json" // Ensure correct type
      },
      body: JSON.stringify(requestBody), // Send modified body
    });
    const dbResponse = await fetch(proxyReq);
    return new Response(dbResponse.body, dbResponse);
  } else {
    // For other methods, just forward
    const dbResponse = await fetch(new Request(targetUrl, req));
    return new Response(dbResponse.body, dbResponse);
  }
}, { port: 8000 });

console.log("Deno proxy with data transformation on http://localhost:8000");

Worker to Deno Proxy Flow

How would a Cloudflare Worker interact with this Deno proxy?

The Worker would simply make a standard HTTP fetch request to the Deno proxy's endpoint. If your Deno proxy is deployed on a platform like Deno Deploy, it will have a public URL.

The Worker sends its request, the Deno proxy processes it (e.g., handles pooling, adds security, transforms data), and then forwards it to the actual database, returning the database's response to the Worker.

Deno Proxy Benefits?

Which of the following are benefits of using a Deno-based database proxy at the edge?

Lesson Summary

In this lesson, we explored how to create efficient database proxies using Deno. We learned that Deno's native HTTP server and security model make it ideal for this task.

We built a basic proxy that forwards requests.
Understood the importance of connection pooling and the proxy's role in it.
Discussed securing your proxy and transforming data at the edge.
Finally, we saw how Cloudflare Workers can interact with such a proxy.

This pattern provides a powerful way to manage database interactions from your edge applications.

常见问题解答

「使用 Deno 构建数据库代理」课时是免费的吗？

是的 — 「使用 Deno 构建数据库代理」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Edge Computing with Cloudflare Workers & Deno 课程的其余内容，请升级到 CoddyKit PRO。 Edge Computing with Cloudflare Workers & Deno 课程共包含 4 节课。

「使用 Deno 构建数据库代理」这节课中我会学到什么？

使用 Deno 和 Workers 创建高效的数据库代理，连接传统数据库或无服务器数据库你通过在浏览器中直接运行的动手代码来练习 Edge Computing with Cloudflare Workers & Deno，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Edge Computing with Cloudflare Workers & Deno 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Edge Computing with Cloudflare Workers & Deno 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 3 节课，共 4 节。

「使用 Deno 构建数据库代理」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Edge Computing with Cloudflare Workers & Deno 课中编写并运行代码吗？

能。每节 Edge Computing with Cloudflare Workers & Deno 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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