How to use static IP address on Google Container Engine (GKE)

#1 Create an static ip address from console or gcloud.

gcloud compute addresses create ip-address --global

#2 Add an annotation of global static ip name to our Ingress object.

kind: Ingress
metadata:
name: nginx
annotations:
kubernetes.io/ingress.global-static-ip-name: "ip-address"
spec:
backend:
serviceName: nginx
servicePort: 80

Thats it! :)