Load Balancer Listeners

5 minutes 5 Questions

Listeners are components of Elastic Load Balancers that take incoming requests and distribute them to one or more registered backend instances. They are configured with a protocol and port number for incoming connections, along with a default rule defining how to route requests to target instances.…

Guide to Load Balancer Listeners

What it is: A Listener in Load Balancing is a process that checks for connection requests. It is configured with a protocol and a port for front-end (client to load balancer) and backend (load balancer to back-end instances) connections. The common protocols include HTTP, HTTPS, TCP, and SSL.

Why it is Important: Load Balancer Listeners allow the Load Balancer to distribute the incoming traffic evenly across multiple target instances, which enhances the performance and fault tolerance of your applications.

How it Works: When a client sends a request, the listener checks the load balancer for connection requests from clients using the specified protocol and port. Once a request is received, it decides where to route the request based on the configured load balancing algorithm.

Exam Tips: Understanding how Load Balancer Listeners work is fundamental in Exam. You should be aware of the different types of listeners, their protocols, and how they operate. Note that you may encounter questions about the routing algorithm, ensuring that the listener is configured correctly for the type of connection and traffic you expect to manage, and the implications of these configurations on the performance and reliability of your applications.

Answering Questions on Load Balancer Listeners: 1. Understand the different types of Load Balancers and their corresponding listeners 2. Familiarize yourself with the effects of different configurations on application performance and reliability 3. Be able to explain how a listener routes traffic to target instances 4. Understand the function of health checks in conjunction with Load Balancer listeners.

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AWS Certified Solutions Architect - Load Balancer Listeners Example Questions

Test your knowledge of Load Balancer Listeners

Question 1

You need to configure SSL offloading on an AWS Classic Load Balancer for a web application whose EC2 instances listen on port 80. Which listener configuration implements SSL offloading so that the load balancer terminates TLS and forwards plaintext traffic to the instances?

Create a listener with Load Balancer protocol HTTPS on port 443 (with an SSL/TLS certificate) and Instance protocol HTTP on port 80. Create the listener with HTTPS as the protocol for the frontend and HTTPS for the backend on port 443. Create the listener with TCP as the protocol for the frontend and HTTP for the backend on port 443. Create the listener with HTTP as the protocol for the frontend and HTTP for the backend on port 80.

Correct Answer: Create a listener with Load Balancer protocol HTTPS on port 443 (with an SSL/TLS certificate) and Instance protocol HTTP on port 80.

SSL offloading (TLS termination) on a Classic Load Balancer means the ELB handles the TLS handshake and decryption. To accomplish this, you configure an HTTPS listener on the load balancer (port 443) and attach a certificate. The load balancer then forwards the decrypted traffic to the targets over HTTP, typically on port 80. Using HTTP on both sides provides no encryption. Using TCP on the front end does not terminate TLS and cannot map to HTTP on the back end for CLB. Using HTTPS on both front end and back end preserves end-to-end encryption and does not offload TLS from the instances.

Question 2

You have recently migrated your application to AWS, and it's now using an Application Load Balancer for distributing incoming client requests. Your application has dynamic content and requires a sticky session. What action should you take?

Enable the stickiness on your ALB target group. Add a latency metric to your ALB Listener. Enable cross-zone load balancing. Add a sticky session to your instances.

Correct Answer: Enable the stickiness on your ALB target group.

To have a sticky session using an Application Load Balancer, enabling stickiness on target groups is necessary. ALB supports sticky sessions by attaching a cookie to each request directed towards target group, ensuring that a specific target instance handles future requests initiated by the user.

Question 3

Your e-commerce application is fronted by an Application Load Balancer (ALB). The security team reports a surge in malicious HTTP requests, including SQL injection and cross-site scripting attempts, as well as occasional HTTP floods that are degrading performance. You need an inline control on the ALB to inspect and block these application-layer attacks. Which security feature should you enable to most effectively reduce the likelihood of these incidents?

Enable AWS WAF on the Application Load Balancer. Disable the existing Listener, and create a new Listener. Enable Amazon GuardDuty on the Application Load Balancer. Configure Direct Connect for the Application Load Balancer.

Correct Answer: Enable AWS WAF on the Application Load Balancer.

AWS WAF integrates directly with an Application Load Balancer to provide inline inspection and blocking of application-layer traffic. It offers managed rule groups for common web exploits like SQL injection and cross-site scripting, as well as rate-based rules to throttle HTTP floods, thereby reducing the likelihood and impact of such incidents before they reach your targets. Disabling and recreating a listener does not provide security filtering. AWS Direct Connect is a private network connectivity service and does not mitigate web attacks. Amazon GuardDuty is an account-level threat detection service that analyzes logs and network telemetry; it is not an inline control and cannot be enabled on an ALB to block malicious requests.

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