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Elastic Load Balancer - Sticky Sessions

  • It is possible to implement stickiness so that the same client is always redirected to the same instance behind a load balancer
  • This works for Classic Load Balancers & Application Load Balancers
  • The "cookie" used for stickiness has an expiration date you control
  • Use case: make sure the user doesn't lose his session data
  • Enabling stickiness may bring imbalance to the load over the backend EC2 instances
  • Application-based cookies
    • Custom cookie
      • Generated by the target
      • Can include any custom attributes required by the application
      • Cookie name must be specified individually for each target group
      • Don't use AWSALB, AWSALBAPP or AWSALBTG (reserved for use by the ELB)
    • Application cookie
      • Generated by the load balancer
      • Cookie name is AWSALBAPP
  • Duration-based cookies
    • Cookie generated by the load balancer
    • Cookie name is AWSALB for ALB, AWSELB for CLB