Summary: Sticky Sessions in AWS Elastic Load Balancing

Sticky sessions, also known as session affinity, allow client requests to be consistently routed to the same backend instance behind a load balancer. This ensures that a user's session data is preserved, which is particularly useful for maintaining user login states and other important information.

Key Points:

• Purpose of Sticky Sessions: To ensure a client's requests are handled by the same backend instance to maintain session data.
• Supported Load Balancers: Sticky sessions can be enabled on Classic Load Balancer (CLB), Application Load Balancer (ALB), and Network Load Balancer (NLB).
• Mechanism: Sticky sessions work by using a special cookie with an expiration date that is sent from the client to the load balancer.
• Cookie Types:
  • Application-based Cookie: Custom cookie generated by the target application with specific attributes.
  • Duration-based Cookie: Generated by the load balancer with a specified expiration time.
• Cookie Names:
  • Avoid using reserved names such as AWSALB, AWSALBAPP, and AWSALBTG.
  • The ALB uses AWSALBAPP for application-generated cookies and AWSALB for duration-based cookies.
  • The CLB uses AWSELB for duration-based cookies.
• Configuration:
  • Sticky sessions are configured at the target group level.
  • Two types of stickiness: load balancer generated (duration-based) or application-based.
  • Duration can be set between one second and seven days.

Enabling Sticky Sessions:

1. Go to the target group settings.
2. Choose "Edit Attributes".
3. Select "Stickiness" and configure the type and duration.
4. Specify a custom cookie name if using application-based stickiness.

Monitoring Sticky Sessions:

• Use web developer tools to inspect network requests and observe the sticky session cookies being passed back and forth between the client and the load balancer.

Considerations:

• Load Imbalance: Sticky sessions can cause an uneven distribution of load across backend instances.
• Disabling Stickiness: You can revert to normal load balancing behavior by disabling stickiness in the target group attributes.

Debugging: