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Sticky Session

This example demonstrates how to achieve session affinity using cookies


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

Name Description Values Sets the affinity type string (in NGINX only cookie is possible Name of the cookie that will be used string (default to INGRESSCOOKIE) The value is a date as UNIX timestamp that the cookie will expire on, it corresponds to cookie Expires directive number of seconds Number of seconds until the cookie expires that will correspond to cookie Max-Age directive number of seconds

You can create the ingress to test this

kubectl create -f ingress.yaml


You can confirm that the Ingress works.

$ kubectl describe ing nginx-test
Name:           nginx-test
Namespace:      default
Default backend:    default-http-backend:80 (,
  Host                          Path    Backends
  ----                          ----    --------     
                                /        nginx-service:80 (<none>)
  affinity: cookie
  session-cookie-name:      INGRESSCOOKIE
  session-cookie-expires: 172800
  session-cookie-max-age: 172800
  FirstSeen LastSeen    Count   From                SubObjectPath   Type        Reason  Message
  --------- --------    -----   ----                -------------   --------    ------  -------
  7s        7s      1   {nginx-ingress-controller }         Normal      CREATE  default/nginx-test

$ curl -I
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; Expires=Sun, 12-Feb-17 14:11:12 GMT; Max-Age=172800; 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, it contains the hash of the used upstream in that request and has an expires. 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.