能否在单个CNAME下对两个目标进行A/B测试并实现动态路由？

Absolutely, you can pull off both A/B testing and dynamic routing for your two Heroku apps under the fixed app.domain.com CNAME using Cloudflare Workers. This is actually a common, well-suited use case for Workers—they let you intercept and redirect requests on the fly while keeping the user-facing URL completely unchanged.

How to Make This Work #

1. Pre-Setup in Cloudflare #

• First, configure app.domain.com as a CNAME record in Cloudflare’s DNS panel. You can point it to either of your Heroku apps (e.g., a-test.herokuapp.com)—the Worker will override this target anyway.
• Make sure the orange cloud proxy status is enabled for this record so requests pass through Cloudflare’s network.

2. Create a Cloudflare Worker with Routing Logic #

Build a new Worker and use this code to handle traffic splitting and user stickiness (so users stay in the same test group on repeat visits):

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

async function handleRequest(request) {
  // Check if the user already has a test group cookie
  const cookieHeader = request.headers.get('Cookie')
  let targetHost = 'a-test.herokuapp.com' // Default to control group

  // Assign or retain the user's test group
  if (cookieHeader && cookieHeader.includes('ab_test_group=b')) {
    targetHost = 'b-test.herokuapp.com'
  } else if (!cookieHeader || Math.random() < 0.5) {
    // 50% chance to assign to B group (adjust 0.5 to tweak split ratio)
    targetHost = 'b-test.herokuapp.com'
  }

  // Modify the request to point to the target Heroku app
  const modifiedRequest = new Request(request.url, {
    method: request.method,
    headers: new Headers(request.headers),
    body: request.body,
    redirect: 'follow'
  })
  modifiedRequest.headers.set('Host', targetHost)

  // Fetch the response from the target app
  const response = await fetch(modifiedRequest)

  // Create a new response to set/update the test group cookie (30-day expiry)
  const finalResponse = new Response(response.body, response)
  const groupValue = targetHost === 'b-test.herokuapp.com' ? 'b' : 'a'
  finalResponse.headers.set(
    'Set-Cookie',
    `ab_test_group=${groupValue}; Path=/; Max-Age=2592000; SameSite=Lax`
  )

  return finalResponse
}

3. Key Code Breakdown #

• User Stickiness: The ab_test_group cookie ensures users stay in their assigned group for 30 days (adjust Max-Age to change this duration).
• Traffic Split: The Math.random() < 0.5 line sets a 50/50 split—tweak the decimal value (e.g., 0.3 for 30% traffic to the B group) to match your test needs.
• Invisible Routing: By modifying the Host header, we send the request to the correct Heroku app while keeping app.domain.com visible to the user.

Official Cloudflare Resources #

You can dive deeper into relevant topics in Cloudflare’s official docs:

• Worker Fetch API: Learn how to intercept and modify requests/responses.
• Cookie Handling in Workers: Best practices for setting and managing user cookies.
• A/B Testing Recipes: Cloudflare provides pre-built examples for A/B testing scenarios in their Workers guide.

Quick Notes #

• Ensure your Heroku apps allow CORS requests from app.domain.com (update their CORS settings if you run into cross-origin errors).
• Bind the Worker to the app.domain.com/* route in Cloudflare’s Worker dashboard to activate it for all requests to your domain.

内容的提问来源于stack exchange，提问作者bteng22