Load Balancer Stickiness, also known as session persistence, is a feature of load balancers that ensures all requests from a single user or client are directed to the same backend server for the duration of a session. This behavior helps maintain session state and provides a consistent experience for users.
In a typical load balancing scenario, incoming requests are distributed across multiple backend servers to balance the load and improve performance. However, certain applications, especially those maintaining user sessions, require subsequent requests from the same client to be handled by the same server. Load balancer stickiness ensures this by binding a client’s session to a specific backend server.
Load balancer stickiness works by assigning a unique identifier to each client and storing this identifier in a cookie or other mechanism. When a request is received, the load balancer checks for this identifier and directs the request to the same backend server that handled the initial request.
Key components include:
Implementing load balancer stickiness offers several advantages:
Stickiness ensures that a user’s session is consistently handled by the same backend server, which is critical for applications that maintain session state, such as e-commerce sites, online banking, and user-specific dashboards.
By keeping user sessions on the same server, stickiness reduces the overhead of fetching session data from a shared store or synchronizing session state across multiple servers, leading to lower latency.
Stickiness simplifies session management by reducing the need for session state replication across servers. This can reduce complexity and overhead in maintaining session consistency.
For applications that rely heavily on session data, stickiness improves performance by avoiding the overhead associated with distributing session state across multiple servers.
Using stickiness with SSL/TLS termination ensures that all requests in a session are handled securely by the same backend server, reducing the risk of session hijacking and other security issues.
Here are some practical examples of how load balancer stickiness can be implemented and utilized:
AWS ELB allows you to enable stickiness for your load balancer using the AWS Management Console or AWS CLI.
aws elb create-load-balancer-policy \<br> --load-balancer-name my-load-balancer \<br> --policy-name my-cookie-policy \<br> --policy-type-name AppCookieStickinessPolicyType \<br> --policy-attributes AttributeName=CookieName,AttributeValue=my-app-cookie<br><br>aws elb set-load-balancer-policies-of-listener \<br> --load-balancer-name my-load-balancer \<br> --load-balancer-port 80 \<br> --policy-names my-cookie-policy<br>Nginx can be configured to use stickiness based on IP hashing or cookies.
http {<br> upstream backend {<br> ip_hash;<br> server backend1.example.com;<br> server backend2.example.com;<br> }<br><br> server {<br> location / {<br> proxy_pass http://backend;<br> }<br> }<br>}<br>http {<br> upstream backend {<br> server backend1.example.com;<br> server backend2.example.com;<br><br> sticky cookie srv_id expires=1h domain=.example.com path=/;<br> }<br><br> server {<br> location / {<br> proxy_pass http://backend;<br> }<br> }<br>}<br>HAProxy can use cookies to enable stickiness.
frontend http_front<br> bind *:80<br> default_backend http_back<br><br>backend http_back<br> balance roundrobin<br> cookie SERVERID insert indirect nocache<br> server backend1 192.168.1.1:80 cookie A<br> server backend2 192.168.1.2:80 cookie B<br>The purpose of load balancer stickiness is to ensure that all requests from a single client are directed to the same backend server for the duration of a session. This helps maintain session state and provides a consistent experience for users.
Load balancer stickiness works by assigning a unique identifier to each client and storing this identifier in a cookie or another mechanism. The load balancer uses this identifier to direct subsequent requests from the same client to the same backend server that handled the initial request.
The benefits of load balancer stickiness include a consistent user experience, reduced latency, simplified session management, improved performance for stateful applications, and enhanced security by ensuring that all requests in a session are handled by the same backend server.
You can enable stickiness in AWS ELB using the AWS Management Console or AWS CLI. In the console, navigate to the “Load Balancers” section, choose your load balancer, edit the stickiness settings, and enable “Stickiness”. In the CLI, use the create-load-balancer-policy and set-load-balancer-policies-of-listener commands.
Applications that benefit most from load balancer stickiness are those that maintain session state and require a consistent user experience. Examples include e-commerce sites, online banking, user-specific dashboards, and any application where session data is critical for functionality.
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