Building Microservices with Deno, Reno, and PostgreSQL

This tutorial demonstrates building microservices with Deno and Reno, a lightweight Deno routing library. We'll create a microservice interacting with a database.

Deno, a secure JavaScript/TypeScript runtime, improves upon Node.js by simplifying module management and aligning APIs with browser standards. While fundamentally different, their application potential largely overlaps. Node.js excels at HTTP services, a strength Deno shares.

Key Concepts:

• Deno's secure environment and browser-aligned APIs are ideal for HTTP services.
• Deno's std/http module enables simple HTTP server creation and basic routing.
• Reno streamlines route declaration and HTTP method management, improving code organization.
• PostgreSQL integration via deno-postgres facilitates robust database operations.
• Custom error classes enhance error handling clarity in client-server communication.
• Deno, Reno, and PostgreSQL combine for scalable, efficient microservice development.

Simple HTTP Servers with std/http:

Before introducing Reno, let's build a basic HTTP server using Deno's standard library. Install Deno (e.g., curl -fsSL https://deno.land/x/install/install.sh | sh -s v1.3.0 on Unix-like systems). Update to version 1.3.0 or later if necessary (deno upgrade --version 1.3.0). Verify the installation with deno --version.

Create server.ts:

<code class="language-typescript">import { listenAndServe } from "https://deno.land/std@0.65.0/http/mod.ts";

const BINDING = ":8000";

console.log(`Listening on ${BINDING}...`);

await listenAndServe(BINDING, (req) => {
  req.respond({ body: "Hello world!" });
});</code>

Run with deno run --allow-net server.ts. The --allow-net flag grants network access.

Improving std/http for Complex Services:

The basic std/http server is limited. Let's enhance it to handle a /messages endpoint (GET for retrieving, POST for adding messages). We'll add conditional checks for URL and HTTP methods.

Reno for Route Management:

For multiple endpoints, manually managing routes becomes cumbersome. Reno simplifies this. Let's rebuild our message service using Reno:

<code class="language-typescript">// ... (imports, including Reno) ...

const routes = createRouteMap([
  [
    "/messages",
    forMethod([
      ["GET", getMessages],
      ["POST", withJsonBody<messagepayload>(addMessage)],
    ]),
  ],
]);

const router = createRouter(routes);

// ... (server setup using the router) ...</messagepayload></code>

Reno handles path parsing and HTTP method management, allowing focus on application logic. It's a router-as-a-function, easily integrated into existing Deno services.

Building a Blog Microservice:

We'll build a blog post microservice with PostgreSQL using the deno-postgres module. The /posts endpoint will support GET (all posts, single post by ID), POST (create post), and PATCH (update post). (Detailed code for this section is omitted for brevity but is available in the original text.)

Error Handling:

Custom error classes improve error handling. For example, a PostNotFoundError class can be created to handle missing posts, returning a 404 instead of a generic error.

Summary:

While std/http suffices for simple services, Reno significantly improves microservice development by simplifying route management and error handling. For larger projects, a framework like Oak might be preferred, but Reno's lightweight nature is ideal for many microservices.

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