I just renew the certificate with the LE prod ACME server but SSLLabs still show the same result as subject mismatch.
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I personally believe this isn't Traefik fault but the testing method used by SSLLabs. In their website footnote:
4. Interoperability issues
In some rare cases trust cannot be established because of interoperability issues between our code and the code or configuration running on the server. We manually review such cases, but if you encounter such an issue please feel free to contact us. Such problems are very difficult to troubleshoot and you may be able to provide us with information that might help us determine the root cause.
I know it will be alright but still trigger me little bit.
I wounder if it is a bug. When ssl labs sents a sslv3 request, Traefik shouldn't be serving a certificate but terminate the connection (or whatever appropriate). I wasn't able to recreate in CURL but it actually what Traefik is doing.