Facing net::ERR_HTTP2_PROTOCOL_ERROR, net::ERR_HTTP3_PROTOCOL_ERROR, and net::ERR_INCOMPLETE_CHUNKED_ENCODING on CloudFront

These protocol errors you're experiencing with CloudFront suggest there's likely a communication issue between CloudFront and your origin server. Here's what might be happening and how to troubleshoot:

The progression of errors (HTTP/3 → HTTP/2 → chunked encoding) indicates that the problem persists across protocols but manifests differently. This typically points to an origin server issue rather than a CloudFront configuration problem.

Possible causes:

1. Origin server configuration issues: Your origin might be terminating connections prematurely or sending malformed responses that don't comply with the HTTP protocol specifications.

2. Content size or timeout issues: If your dynamic content generation takes too long or produces very large responses, it might exceed CloudFront's timeout settings or buffer limits.

3. SSL/TLS negotiation problems: There could be a mismatch between the SSL/TLS settings on your origin and what CloudFront is configured to use.

4. Origin response headers: Incorrect or conflicting headers in your origin's response might be causing protocol errors.

Debugging steps:

1. Check your origin server logs for any errors or warnings that coincide with these CloudFront errors.

2. Temporarily bypass CloudFront and access your origin directly to see if the issue persists.

3. Review your origin's response headers, particularly those related to content length, transfer encoding, and connection management.

4. Examine the origin response timeout settings in your CloudFront distribution and consider increasing them if your dynamic content generation takes longer.

5. If using a custom origin, verify that the SSL/TLS certificate is valid and properly configured.

Best practices:

1. For dynamic content, ensure your origin server properly sets content length headers or uses chunked transfer encoding correctly.

2. Consider implementing compression at the origin to reduce response sizes.

3. Optimize your dynamic content generation to respond within CloudFront's timeout limits.

4. If using custom headers between CloudFront and your origin, verify they're correctly formatted.

5. For large dynamic responses, consider breaking them into smaller, more manageable chunks.

If the issue persists after these steps, you might need to capture and analyze the network traffic between CloudFront and your origin to identify exactly where the protocol errors are occurring.
Sources
Troubleshooting error response status codes in CloudFront - Amazon CloudFront
Troubleshoot CloudFront distribution access issues with CNAMEs and custom origins | AWS re:Post
HTTP 502 status code (Bad Gateway) - Amazon CloudFront