Adds procedure proxying https traffic between clusters.

kubernetes/ingress/proxy_traffic.md

+Procedure to proxy from one cluster to another to avoind down time when moving workload between clusters and updating dns.
+
+Deploy the app on the new cluster.
+
+Create an svc on the first cluster:
+
+```
+apiVersion: v1
+kind: Service
+metadata:
+  name: acme-libre-sh
+  namespace: libre-sh
+spec:
+  type: ExternalName
+  externalName: cluster.beta.liiib.re
+```
+
+Update your ingress to add the proxy for port 80, to get the cert made on the new cluster:
+
+```
+apiVersion: extensions/v1beta1
+kind: Ingress
+metadata:
+  name: libre-sh
+  namespace: libre-sh
+spec:
+  rules:
+  - host: k8s.libre.sh
+    http:
+      paths:
+      - backend:
+          serviceName: acme-libre-sh
+          servicePort: 80
+        path: /.well-known/acme-challenge
+      - backend:
+          serviceName: libresh-web
+          servicePort: http
+        path: /
+  tls:
+  - hosts:
+    - k8s.libre.sh
+    secretName: k8s-libresh-tls
+```
+
+Once the cert is created on the second cluster, proxy all the traffic with an https backend:
+
+```
+apiVersion: extensions/v1beta1
+kind: Ingress
+metadata:
+  name: libre-sh
+  namespace: libre-sh
+  annotations:
+    nginx.ingress.kubernetes.io/backend-protocol: HTTPS
+spec:
+  rules:
+  - host: k8s.libre.sh
+    http:
+      paths:
+      - backend:
+          serviceName: acme-libre-sh
+          servicePort: 443
+        path: /
+  tls:
+  - hosts:
+    - k8s.libre.sh
+    secretName: k8s-libresh-tls
+```