istio ingress gateway needs secrets in istio-system issue code example
Example: istio setup ssl
$ kubectl create -n istio-system secret tls httpbin-credential --key=httpbin.example.com.key --cert=httpbin.example.com.crt
$ kubectl create -n istio-system secret tls httpbin-credential --key=httpbin.example.com.key --cert=httpbin.example.com.crt