Exploring Sticky Sessions in EC2 Load Balancer: Theory and Practical Demonstration

we’re going to delve into a crucial feature of EC2 Load Balancer called Sticky Sessions. This feature is a game-changer when it comes to enhancing user experience and ensuring seamless sessions. So, let’s jump right in and understand the theory behind sticky sessions, followed by a hands-on demonstration.

Understanding Sticky Sessions

Before we dive into the practical demonstration, let’s grasp the theory behind sticky sessions. Consider an architecture where a legacy application is deployed behind an EC2 Load Balancer with multiple instances. Without sticky sessions, a user’s session can be lost when they’re directed to a different instance during subsequent requests. This leads to a poor user experience and a lack of continuity in the application.

The Role of Sticky Sessions

With sticky sessions enabled, the same user’s requests are directed to the same instance across multiple requests. This is achieved through cookies set on the user’s device, ensuring that their session is maintained on the same instance. Sticky sessions are particularly useful for legacy applications that store sessions on EC2 instances.

Practical Demonstration

  1. Setup and Configuration:
    • Instances: Set up EC2 instances and assign them numbers (e.g., Instance 1, Instance 2, Instance 3).
    • Load Balancer: Create an EC2 Load Balancer and configure target groups for instances.
  2. Testing Default Behavior:
    • Open instances on browsers to observe the page content (e.g., “Instance Number 1”).
    • Access the Load Balancer DNS and notice that requests are distributed across instances on each refresh.
  3. Enabling Sticky Sessions:
    • Enable Sticky Sessions in the target group settings of the Load Balancer.
    • Sticky sessions can be load balancer-generated or application-based cookies.
  4. Practical Demonstration:
    • Open developer tools and check the cookies panel to see that no cookies are initially set.
    • Reload the page and observe that the Load Balancer generates a cookie and directs requests to an instance.
    • The cookie stores information about the instance, ensuring that future requests from the same user go to the same instance.
    • Deleting the cookie leads to requests being distributed across instances again.
  5. Disabling Sticky Sessions:
    • Disable Sticky Sessions in the target group settings of the Load Balancer.
    • Observe how requests are once again distributed across instances with each refresh.

Key Takeaways

  • Sticky sessions ensure that a user’s session is maintained on the same instance for consecutive requests.
  • This feature is particularly useful for legacy applications that store sessions on EC2 instances.
  • Sticky sessions are configured on target groups within the EC2 Load Balancer settings.
  • Modern applications often use external session stores like DynamoDB or Redis to avoid such issues.


Sticky sessions play a vital role in ensuring a seamless user experience in applications hosted behind EC2 Load Balancers. By understanding the theory and witnessing the practical demonstration, you’ve gained insights into how this feature can be used to preserve user sessions and maintain continuity in legacy applications.

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