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# Sticky Session

This example demonstrates how to achieve session affinity using cookies

## Deployment

Session stickiness is achieved through 3 annotations on the Ingress, as shown in the example.

Name | Description | Values
--- | --- | ---
nginx.ingress.kubernetes.io/affinity | Sets the affinity type | string (in NGINX only `cookie` is possible
nginx.ingress.kubernetes.io/session-cookie-name | Name of the cookie that will be used | string (default to INGRESSCOOKIE)
nginx.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

    kubectl create -f ingress.yaml

## Validation

You can confirm that the Ingress works.

    $ 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:      INGRESSCOOKIE
    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: INGRESSCOOKIE=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: INGRESSCOOKIE' setting the right defined stickiness 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.

When you have more than one Ingress Object pointing to the same Service, but one containing affinity configuration and other don't, the first created Ingress will be used. This means that you can face the situation that you've configured Session Affinity in one Ingress and it doesn't reflects in NGINX configuration, because there is another Ingress Object pointing to the same service that doesn't configure this.