ingress-server-snippet.yaml

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    nginx.ingress.kubernetes.io/server-snippet: |
        set $agentflag 0;

        if ($http_user_agent ~* "(Mobile)" ){
          set $agentflag 1;
        }

        if ( $agentflag = 1 ) {
          return 301 https://m.example.com;
        }