§2024-06-04

HAProxy, a high-performance TCP/HTTP load balancer, typically does not emit 404 errors directly because it acts as an intermediary between clients and backend servers. A 404 (Not Found) error indicates that the requested resource could not be found on the server, which is usually the responsibility of the backend server, not HAProxy.

However, there are scenarios where HAProxy might indirectly be involved in a 404 error:

Backend Server Response: If HAProxy forwards a request to a backend server and that server responds with a 404 error because the requested resource is not found, HAProxy will relay this 404 error back to the client.

Misconfiguration: If HAProxy is misconfigured or the backend servers are not properly set up (e.g., incorrect routing rules or non-existent endpoints), it might cause a 404 error on the backend server, which HAProxy will then forward to the client.

Custom Error Pages: Although HAProxy itself doesn't generate 404 errors, it can be configured to serve custom error pages for different HTTP status codes, including 404. This means if a backend server returns a 404 error, HAProxy can intercept that response and return a custom 404 page instead of the default one from the backend server.

To summarize, HAProxy does not inherently generate 404 errors but can relay them from backend servers to clients. Proper configuration and ensuring backend servers are correctly set up can help avoid unintentional 404 errors.