proxy

@astroscope/proxy

Note: This package is in active development. APIs may change between versions.

HTTP proxy for Astro — strangler fig migrations and API gateway. Gradually migrate from any backend or proxy to upstream APIs.

Examples

• demo/proxy - API proxy to JSONPlaceholder
• demo/proxy-migration - Strangler fig migration pattern

Why?

Astro has no built-in proxy support (roadmap discussion #665). This package fills that gap with two powerful patterns:

• Strangler fig migration - Gradually migrate any website to Astro - WordPress, Rails, Django, .NET, PHP, or anything else. New Astro pages take precedence while unhandled requests fall through to your existing site.
• Standalone gateway - Run Astro in standalone mode while proxying to your backend APIs. No need to embed Astro as middleware in Express/Fastify just because you need features like startup hooks or API proxying - use @astroscope/boot for lifecycle and this package for proxying.

Installation

npm install @astroscope/proxy

Usage

Migration (Strangler Fig)

When migrating from a legacy backend, create a catch-all route that forwards unhandled requests to the old system. As you build new pages in Astro, they take precedence over the catch-all, gradually "strangling" the legacy backend.

// src/pages/[...legacy].ts
import { createProxyHandler } from "@astroscope/proxy";

export const ALL = createProxyHandler({
  upstream: process.env.LEGACY_BACKEND!,
});

The ALL export handles all HTTP methods (GET, POST, PUT, DELETE, PATCH, HEAD).

With this setup:

• src/pages/index.astro → handled by Astro
• src/pages/about.astro → handled by Astro
• /old-page (no Astro file) → proxied to legacy backend

API Proxy

For proxying specific paths to an upstream API:

// src/pages/api/[...path].ts
import { createProxyHandler } from "@astroscope/proxy";

export const ALL = createProxyHandler({
  upstream: process.env.API_UPSTREAM!,
});

Options

upstream (required)

The base URL of the upstream server.

createProxyHandler({
  upstream: "https://legacy.example.com",
});

onRequest (optional)

Called before proxying. Can modify the request or short-circuit with a Response.

Useful for adding headers, authentication, logging, rewriting URLs or blocking requests.

createProxyHandler({
  upstream: "https://api.example.com",
  onRequest: (context, targetUrl) => {
    const headers = new Headers(context.request.headers);

    headers.set("Authorization", `Bearer ${getToken()}`);

    return new Request(context.request, { headers });
  },
});

To short-circuit (skip proxying):

onRequest: (context, targetUrl) => {
  if (targetUrl.pathname === "/blocked") {
    return new Response("Not allowed", { status: 403 });
  }
};

To override the pathname (e.g., use original path before any rewrites):

onRequest: (context, targetUrl) => {
  targetUrl.pathname = context.originPathname;
};

onResponse (optional)

Called after receiving a response from upstream. Can modify the response.

createProxyHandler({
  upstream: "https://api.example.com",
  onResponse: (context, response, targetUrl) => {
    const headers = new Headers(response.headers);

    headers.set("X-Proxied-By", "astro");

    return new Response(response.body, {
      status: response.status,
      headers,
    });
  },
});

onError (optional)

Called when an error occurs during proxying. Can return a custom error response.

createProxyHandler({
  upstream: "https://api.example.com",
  onError: (context, error, targetUrl) => {
    console.error(`Proxy failed: ${targetUrl}`, error);

    return new Response("Service temporarily unavailable", {
      status: 503,
      headers: { "Retry-After": "30" },
    });
  },
});

If not provided, returns a default 502 response.

client (optional)

HTTP client configuration for connection pooling and HTTP/2.

createProxyHandler({
  upstream: "https://api.example.com",
  client: {
    pipelining: 10,            // max concurrent requests per origin (default: 10)
    allowH2: true,             // enable HTTP/2 (default: true)
    maxConcurrentStreams: 128, // HTTP/2 max streams (default: 128)
    keepAliveTimeout: 60000,   // keep-alive timeout in ms (default: 60000)
  },
});

Features

• HTTP/2 support with connection pooling (via undici)
• Proper stream handling for large responses
• Request cancellation support
• Handles 204/304 responses correctly

Requirements

• Node.js runtime (required by undici)
• Astro 5.x with SSR output mode

License

MIT