Sticky sessions

This example demonstrates how to achieve session affinity using cookies.

Deployment

Session affinity can be configured using the following annotations:

Name	Description	Value
nginx.ingress.kubernetes.io/affinity	Type of the affinity, set this to cookie to enable session affinity	string (nginx only supports cookie)
nginx.ingress.kubernetes.io/affinity-mode	The affinity mode defines how sticky a session is. Use balanced to redistribute some sessions when scaling pods or persistent for maximum stickyness.	balanced (default) or persistent
nginx.ingress.kubernetes.io/session-cookie-name	Name of the cookie that will be created	string (defaults to INGRESSCOOKIE)
nginx.ingress.kubernetes.io/session-cookie-path	Path that will be set on the cookie (required if your Ingress paths use regular expressions)	string (defaults to the currently matched path)
nginx.ingress.kubernetes.io/session-cookie-max-age	Time until the cookie expires, corresponds to the Max-Age cookie directive	number of seconds
nginx.ingress.kubernetes.io/session-cookie-expires	Legacy version of the previous annotation for compatibility with older browsers, generates an Expires cookie directive by adding the seconds to the current date	number of seconds
nginx.ingress.kubernetes.io/session-cookie-change-on-failure	When set to false nginx ingress will send request to upstream pointed by sticky cookie even if previous attempt failed. When set to true and previous attempt failed, sticky cookie will be changed to point to another upstream.	true or false (defaults to false)

You can create the example 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-name:        INGRESSCOOKIE
  session-cookie-expires: 172800
  session-cookie-max-age: 172800
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; 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 that the response contains a Set-Cookie header with the settings we have defined. This cookie is created by NGINX, it contains a randomly generated key corresponding to the upstream used for that request (selected using consistent hashing) and has an Expires directive. If the user changes this cookie, nginx creates a new one and redirects the user to another upstream.

If the backend pool grows 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 re-routed to another upstream server. This does not require the cookie to be updated because the key's consistent hash will change.

When you have a Service pointing to more than one Ingress, with only one containing affinity configuration, the first created Ingress will be used. This means that you can face the situation that you've configured session affinity on one Ingress and it doesn't work because the Service is pointing to another Ingress that doesn't configure this.