Pages Won't Load with Cloudflare Adapter on Start

[asdfjkalsdfla]

Astro Info

Astro                    v6.0.0-beta.11
Vite                     v7.3.1
Node                     v20.19.1
System                   Linux (x64)
Package Manager          npm
Output                   static
Adapter                  @astrojs/cloudflare (v13.0.0-beta.7)
Integrations             none

If this issue only occurs in one browser, which browser is a problem?

No response

Describe the Bug

When starting with cloudflare worker adapter, all pages return a 404.

What's the expected result?

Pages load.

Link to Minimal Reproducible Example

https://stackblitz.com/edit/github-auwgrqay-x23bdnfb

Participation

• I am willing to submit a pull request for this issue.

[astrobot-houston]

I was able to reproduce this issue. The root cause is an IPv4/IPv6 localhost mismatch in the Cloudflare adapter's prerenderer (packages/integrations/cloudflare/src/prerenderer.ts). The Vite preview server is configured with host: 'localhost', which on many systems binds to ::1 (IPv6), but Node.js fetch('http://localhost:PORT') resolves to 127.0.0.1 (IPv4), causing connect ECONNREFUSED. Since the prerendering phase fails, no HTML files are generated, and all routes return 404 when deployed.

Fix: I was able to fix this issue. The fix changes host: 'localhost' to host: '127.0.0.1' and updates the URL construction to use 127.0.0.1 explicitly, ensuring both the server binding and fetch target use the same IPv4 address. All existing tests pass and the reproduction build succeeds with the fix applied. View Suggested Fix

Priority: [P4: important]. This completely breaks astro build for any project using @astrojs/cloudflare with prerendered pages, which is the default configuration. All Cloudflare adapter users on systems where localhost resolves to IPv6 are affected — this is a common configuration on modern Linux systems and CI environments.

Full Triage Report

Issue #15525: Pages Won't Load with Cloudflare Adapter on Start

Original Issue

Title: Pages Won't Load with Cloudflare Adapter on Start
Author: asdfjkalsdfla
URL: #15525
Created: 2026-02-15

Description: When starting with the Cloudflare worker adapter, all pages return a 404.

Expected result: Pages load.

Reproduction: https://stackblitz.com/edit/github-auwgrqay-x23bdnfb

Environment Details

From the issue:

• Astro: v6.0.0-beta.11
• Vite: v7.3.1
• Node: v20.19.1
• System: Linux (x64)
• Package Manager: npm
• Output: static
• Adapter: @astrojs/cloudflare (v13.0.0-beta.7)
• Integrations: none

Reproduction Result

Reproduced: YES

The bug is consistently reproducible. Running astro build with the Cloudflare adapter fails during the prerendering phase with a fetch failed / connect ECONNREFUSED error.

Steps to Reproduce

1. Create an Astro project with @astrojs/cloudflare adapter
2. Have at least one prerendered page (the default, since output: 'static' is the default)
3. Run astro build
4. Build fails with fetch failed / connect ECONNREFUSED 127.0.0.1:<port>

Root Cause Analysis

The bug is in packages/integrations/cloudflare/src/prerenderer.ts. The Cloudflare adapter's prerenderer starts a Vite preview server with the Cloudflare Vite plugin (which uses miniflare/workerd) to prerender static pages during the build phase.

The issue is an IPv4/IPv6 mismatch:

1. The prerenderer creates a Vite preview server with host: 'localhost' (line 54 of prerenderer.ts)
2. When Vite resolves localhost, it may bind to ::1 (IPv6 localhost) depending on the system's DNS configuration
3. The prerenderer then constructs the URL as http://localhost:${address.port} (line 63)
4. When Node.js's fetch (undici) resolves localhost, it tries 127.0.0.1 (IPv4) first
5. The server is listening on ::1 (IPv6) but the fetch connects to 127.0.0.1 (IPv4), resulting in ECONNREFUSED

Verification:

• A plain Vite preview server with host: 'localhost' binds to {"address":"::1","family":"IPv6","port":XXXXX}
• Node.js fetch('http://localhost:PORT') results in connect ECONNREFUSED 127.0.0.1:PORT
• This confirms the IPv4/IPv6 address mismatch

Fix

Changed packages/integrations/cloudflare/src/prerenderer.ts to use 127.0.0.1 (explicit IPv4 loopback) instead of localhost in two places:

1. Line 54: Preview server host configuration: 'localhost' → '127.0.0.1'
2. Line 63: Server URL construction: http://localhost:${address.port} → http://127.0.0.1:${address.port}

--- a/packages/integrations/cloudflare/src/prerenderer.ts
+++ b/packages/integrations/cloudflare/src/prerenderer.ts
@@ -51,7 +51,7 @@
 				},
 				root: fileURLToPath(root),
 				preview: {
-					host: 'localhost',
+					host: '127.0.0.1',
 					port: 0,
 					open: false,
 				},
@@ -60,7 +60,7 @@
 
 			const address = previewServer.httpServer.address();
 			if (address && typeof address === 'object') {
-				serverUrl = `http://localhost:${address.port}`;
+				serverUrl = `http://127.0.0.1:${address.port}`;
 			} else {
 				throw new Error(

Fix verified: Build succeeds, all existing tests pass (static.test.js, prerender-styles.test.js, routes-json.test.js, routing-priority.test.js — 92/92 pass).

Diagnosis Confidence: high

• The prerenderer was introduced in PR Support prerendering inside of adapter runtimes #15077, merged 2026-02-06 (~9 days before this issue)
• The bug has existed since the initial creation of the file
• The code's own error message acknowledges this class of failure as a bug ("This is likely a bug in @astrojs/cloudflare")
• No prior issues or PRs discuss this IPv4/IPv6 behavior as intentional
• Verdict: bug (not intended behavior)

This report was made by an LLM. Mistakes happen, check important info.