As of today nginx configuration for web socket protocol upgrade is written in uppercase (proxy_set_header Connection "Upgrade";).

• HTTP/2 spec require headers to be in lowercase https://datatracker.ietf.org/doc/html/rfc7540#autoid-55
• It appears that when Traefik is used as ingress in k8s, realtime features (like Kanban) shows "You are disconnected from real time". When the header is written in lower case the message disappear.

Hence, to maximize compatibility, header should be written in lowercase.