使用AWS CloudFront、Namecheap DNS与S3 Bucket托管网站时通过域名访问出现403错误的求助

Let’s walk through the most common fixes for this exact scenario—when your CloudFront and S3 endpoints work fine, but your custom Namecheap domain throws a 403. I’ve debugged this dozens of times, so here’s what to check step by step:

1. Verify CloudFront Custom Domain & SSL Certificate Setup #

First, make sure CloudFront recognizes your custom domain properly:

• Head to your CloudFront distribution → Alternate Domain Names (CNAMEs). Confirm your custom domain (e.g., yourdomain.com, www.yourdomain.com) is listed here. If it’s missing, CloudFront won’t accept requests to that domain, leading to a 403.
• Check the Custom SSL Certificate linked to the distribution. It must be an ACM certificate issued in the us-east-1 (N. Virginia) region, and it needs to cover your exact custom domain (either a specific match or a wildcard like *.yourdomain.com). If the certificate is pending validation or doesn’t include your domain, CloudFront will block requests.

2. Fix Namecheap DNS Record Misconfiguration #

DNS issues are the #1 cause of this problem:

• For subdomains (e.g., www.yourdomain.com): Use a CNAME record pointing directly to your CloudFront distribution domain (e.g., d123456abcdef.cloudfront.net). No http://, https://, or trailing slashes allowed—just the raw CloudFront domain.
• For root domains (e.g., yourdomain.com): Standard CNAME records aren’t allowed for root domains per DNS rules. Instead, use Namecheap’s ALIAS/ANAME record (look for this option in your DNS settings) pointing to your CloudFront domain. If you tried to use a CNAME for the root domain, this will break resolution and trigger 403s.
• Validate DNS resolution: Run nslookup yourdomain.com or dig yourdomain.com in your terminal. The output should show your CloudFront distribution domain as the canonical name. If not, flush your local DNS cache (ipconfig /flushdns on Windows, sudo dscacheutil -flushcache on Mac) and wait for the TTL to expire (set TTL to 5 minutes temporarily for faster testing).

3. Double-Check CloudFront Origin Configuration #

Since you’re using the S3 Static Website Endpoint as your origin:

• Confirm your CloudFront origin domain is the S3 Website Endpoint (e.g., yourbucket.s3-website-us-east-1.amazonaws.com), not the S3 REST API endpoint (e.g., yourbucket.s3.amazonaws.com). Using the REST endpoint will make CloudFront pass the bucket name in requests, leading to S3 403s when accessed via custom domains.
• Ensure the Origin Protocol Policy matches your S3 endpoint’s capabilities. S3 Website Endpoints support HTTP only in some regions, so set this to HTTP and HTTPS if needed (CloudFront will still handle HTTPS for your viewers regardless).

4. Inspect CloudFront Cache Behavior #

A misconfigured cache behavior can block valid requests:

• Go to your distribution’s Cache Behaviors tab. Confirm the behavior for your custom domain allows GET and HEAD methods—these are required for static site content.
• Check the Viewer Protocol Policy: If you set it to Redirect HTTP to HTTPS, make sure you’re testing the HTTPS version of your custom domain. A misconfigured SSL certificate can turn that redirect into a 403.
• If you’re using Lambda@Edge or CloudFront Functions, temporarily disable them to rule out custom code causing the 403.

5. Use Debugging Tools to Narrow Down the Issue #

These commands will help you pinpoint exactly where the 403 is coming from:

• Run curl -v https://yourdomain.com to see the full request/response flow. Look for:
  • If the Server header is CloudFront, the 403 is coming from CloudFront (likely a domain or certificate issue).
  • If the Server header is AmazonS3, the 403 is coming from S3 (double-check your bucket policy or origin path).
• Enable CloudFront access logs (under the Logs tab) and review the entries. Look for fields like cs-host (your custom domain), sc-status (403), and x-edge-detailed-result-type—this will tell you exactly why the request was rejected.

Quick Sanity Check #

Even though you said S3 is public, double-verify:

• Your S3 bucket’s Block Public Access settings are all disabled.
• The bucket policy you shared (PublicReadGetObject) is applied correctly, and the resource ARN matches your bucket name (arn:aws:s3:::cryptocopytradeprod/*).

内容的提问来源于stack exchange，提问作者Guy Hagemans