Client errors (4xx) and business logic failures should not be retried

Retry middleware is expected to retry client errors (4xx) or business logic failures, but Traefik only retries 5xx status codes and network errors by default. Client errors will not succeed on retry.

Understand Traefik's default retry behavior: only 5xx backend responses and network errors (connection refused, reset, timeout) trigger retries. Do not expect 4xx client errors or business logic rejections to be retried automatically.