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 stickiness.	`balanced` (default) or `persistent`
nginx.ingress.kubernetes.io/affinity-canary-behavior	Defines session affinity behavior of canaries. By default the behavior is `sticky`, and canaries respect session affinity configuration. Set this to `legacy` to restore original canary behavior, when session affinity parameters were not respected.	`sticky` (default) or `legacy`
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-secure	Set the cookie as secure regardless the protocol of the incoming request	`"true"` or `"false"`
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-domain	Domain that will be set on the cookie	string
nginx.ingress.kubernetes.io/session-cookie-samesite	`SameSite` attribute to apply to the cookie	Browser accepted values are `None`, `Lax`, and `Strict`
nginx.ingress.kubernetes.io/session-cookie-conditional-samesite-none	Will omit `SameSite=None` attribute for older browsers which reject the more-recently defined `SameSite=None` value	`"true"` or `"false"`
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 session affinity 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   {ingress-nginx-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 the Ingress-Nginx Controller, it contains a randomly generated key corresponding to the upstream used for that request (selected using consistent hashing) and has an Expires directive. If a client sends a cookie that doesn't correspond to an upstream, NGINX selects an upstream and creates a corresponding cookie.

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.

Caveats ¶

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.