Most Asked Interview Questions and Answers on AWS ELB

What is AWS Elastic Load Balancing (ELB) and how does it work?

AWS ELB automatically distributes incoming application traffic across multiple targets, such as EC2 instances, containers, and IP addresses, in one or more Availability Zones. It helps ensure fault tolerance and high availability by routing traffic only to healthy targets.

What are the different types of load balancers available in AWS ELB?

There are three types of load balancers in AWS: Application Load Balancer (ALB): Best suited for HTTP/HTTPS traffic, operates at the application layer (Layer 7). Network Load Balancer (NLB): Handles TCP/UDP traffic at ultra-low latency, operates at the transport layer (Layer 4). Classic Load Balancer (CLB): Operates at both the application and transport layers, primarily used for simple load balancing.

How does an Application Load Balancer (ALB) differ from a Network Load Balancer (NLB)?

ALB is designed for HTTP/HTTPS traffic and supports advanced routing features like host-based and path-based routing, SSL termination, and WebSocket support. NLB, on the other hand, is optimized for TCP/UDP traffic, offering extremely low latencies and the ability to handle millions of requests per second.

What is the concept of Target Groups in AWS ELB?

Target Groups are used to route requests to one or more registered targets (EC2 instances, containers, IP addresses) when using an ALB or NLB. You can define health check settings for each target group to determine the health of its targets.

Explain how sticky sessions work with ELB.

Sticky sessions, also known as session affinity, enable the load balancer to bind a user’s session to a specific target within the target group. This ensures that all requests from the user during the session are sent to the same target, maintaining session persistence.

What are ELB health checks, and how do they function?

ELB health checks monitor the health of the targets in a target group by periodically sending requests to the targets. If a target fails the health checks, ELB stops routing traffic to it until it becomes healthy again. Health checks can be configured with specific settings like ping protocol, ping port, and threshold values.

How do you set up SSL/TLS termination on an ELB?

SSL/TLS termination can be configured on an ALB by uploading the SSL certificate to AWS Certificate Manager (ACM) or IAM, then associating it with the load balancer’s listener. This offloads the SSL decryption from the application servers, reducing their processing burden.

What is cross-zone load balancing, and how does it work in ELB?

Cross-zone load balancing allows a load balancer to evenly distribute traffic across all registered targets in all enabled Availability Zones, rather than just the targets in the zone where the request was received. This feature helps in better utilization of targets and improves overall fault tolerance.

How does Auto Scaling integrate with ELB?

Auto Scaling works with ELB by automatically adding or removing instances from the load balancer’s target group as the number of instances changes. This ensures that traffic is always distributed across the correct set of healthy instances, maintaining performance and availability.

Can you explain the concept of listener rules in an Application Load Balancer (ALB)?

Listener rules in ALB define how incoming requests are routed to targets. Each rule consists of a priority, a condition (like host-header or path pattern), and an action (like forward to a target group, redirect, or return a fixed response). ALB evaluates the rules in priority order to determine how to route the traffic.