Session State and Session Stickiness

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Sticky Sessions with Local Session Caching

Sticky sessions, also known as session affinity, allow you to route a site user to the particular web server that is managing that individual user’s session. The session’s validity can be determined by a number of methods, including a client-side cookies or via configurable duration parameters that can be set at the load balancer which routes requests to the web servers.

Some advantages with utilizing sticky sessions are that it’s cost effective due to the fact you are storing sessions on the same web servers running your applications and that retrieval of those sessions is generally fast because it eliminates network latency.

A drawback for using storing sessions on an individual node is that in the event of a failure, you are likely to lose the sessions that were resident on the failed node. In addition, in the event the number of your web servers change, for example a scale-up scenario, it’s possible that the traffic may be unequally spread across the web servers as active sessions may exist on particular servers. If not mitigated properly, this can hinder the scalability of your applications.

Requirements

An HTTP/HTTPS load balancer.

At least one healthy instance in each Availability Zone.

Duration-based stickiness

Duration-based stickiness routes requests to the same target in a target group using a load balancer generated cookie (AWSALB). The cookie is used to map the session to the target. If your application does not have its own session cookie, you can specify your own stickiness duration and manage how long your load balancer should consistently route the user's request to the same target.

Application-based stickiness

Application-based stickiness gives you the flexibility to set your own criteria for client-target stickiness. When you enable application-based stickiness, the load balancer routes the first request to a target within the target group based on the chosen algorithm. The target is expected to set a custom application cookie that matches the cookie configured on the load balancer to enable stickiness. This custom cookie can include any of the cookie attributes required by the application.

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Sticky Sessions with Local Session Caching

Requirements

Duration-based stickiness

Application-based stickiness

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