How do you debug middleware ordering issues causing unexpected routing behavior?

Start with the Traefik dashboard's router detail view, which lists the exact middleware chain attached to a router in the order it will execute, since a misremembered order in a YAML file is a common source of the bug in the first place.

Raise the log level to DEBUG temporarily; Traefik logs which middlewares a request passes through and, for rejecting middlewares like BasicAuth or ForwardAuth, why the request was stopped, which quickly narrows down whether the issue is ordering versus a misconfigured middleware itself.

Isolate the problem by testing each middleware individually: attach only the suspected middleware to a throwaway router with the same rule and confirm its behavior in isolation before reintroducing the rest of the chain one at a time, which reveals exactly where in the sequence the unexpected behavior starts.

A frequent root cause worth checking explicitly is a shared middleware list reused across multiple routers, where a change intended for one router's chain unintentionally altered behavior for every other router referencing that same shared list, since Traefik doesn't warn about cross-router reuse.