Improve the session affinity feature

examples/affinity/cookie/nginx/README.md

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+# Sticky Session
+
+This example demonstrates how to achieve session affinity using cookies 
+
+## Prerequisites
+
+You will need to make sure you Ingress targets exactly one Ingress
+controller by specifying the [ingress.class annotation](/examples/PREREQUISITES.md#ingress-class),
+and that you have an ingress controller [running](/examples/deployment) in your cluster.
+
+You will also need to deploy multiple replicas of your application that show up as endpoints for the Service referenced in the Ingress object, to test session stickyness.
+Using a deployment with only one replica doesn't set the 'sticky' cookie.
+
+## Deployment
+
+Session stickyness is achieved through 3 annotations on the Ingress, as shown in the [example](sticky-ingress.yaml).
+
+|Name|Description|Values|
+|ingress.kubernetes.io/affinity|Sets the affinity type|string (in NGINX only ``cookie`` is possible|
+|ingress.kubernetes.io/session-cookie-name|Name of the cookie that will be used|string (default to route)|
+|ingress.kubernetes.io/session-cookie-hash|Type of hash that will be used in cookie value|sha1/md5/index|
+
+You can create the ingress to test this
+
+```console
+$ kubectl create -f sticky-ingress.yaml
+```
+
+## Validation
+
+You can confirm that the Ingress works.
+
+```console
+$ kubectl describe ing nginx-test
+Name:			nginx-test
+Namespace:		default
+Address:		
+Default backend:	default-http-backend:80 (10.180.0.4:8080,10.240.0.2:8080)
+Rules:
+  Host	                        Path	Backends
+  ----	                        ----	--------
+  stickyingress.example.com     
+                                /   	 nginx-service:80 (<none>)
+Annotations:
+  affinity:	cookie
+  session-cookie-hash:		sha1
+  session-cookie-name:		route
+Events:
+  FirstSeen	LastSeen	Count	From				SubObjectPath	Type		Reason	Message
+  ---------	--------	-----	----				-------------	--------	------	-------
+  7s		7s		1	{nginx-ingress-controller }			Normal		CREATE	default/nginx-test
+  
+
+$ curl -I http://stickyingress.example.com
+HTTP/1.1 200 OK
+Server: nginx/1.11.9
+Date: Fri, 10 Feb 2017 14:11:12 GMT
+Content-Type: text/html
+Content-Length: 612
+Connection: keep-alive
+Set-Cookie: route=a9907b79b248140b56bb13723f72b67697baac3d; Path=/; HttpOnly
+Last-Modified: Tue, 24 Jan 2017 14:02:19 GMT
+ETag: "58875e6b-264"
+Accept-Ranges: bytes
+```
+In the example above, you can see a line containing the 'Set-Cookie: route' setting the right defined stickness cookie.
+This cookie is created by NGINX containing the hash of the used upstream in that request. 
+If the user changes this cookie, NGINX creates a new one and redirect the user to another upstream.
+
+If the backend pool grows up NGINX will keep sending the requests through the same server of the first request, even if it's overloaded.
+
+When the backend server is removed, the requests are then re-routed to another upstream server and NGINX creates a new cookie, as the previous hash became invalid.
+

examples/affinity/cookie/nginx/sticky-ingress.yaml

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+apiVersion: extensions/v1beta1
+kind: Ingress
+metadata:
+  name: nginx-test
+  annotations:
+    kubernetes.io/ingress.class: "nginx"
+    ingress.kubernetes.io/affinity: "cookie"
+    ingress.kubernetes.io/session-cookie-name: "route"
+    ingress.kubernetes.io/session-cookie-hash: "sha1"
+
+spec:
+  rules:
+  - host: stickyingress.example.com
+    http:
+      paths:
+      - backend:
+          serviceName: nginx-service
+          servicePort: 80
+        path: /