AWS ELB Interview Questions For Beginners & Answers (2025)

Elastic Load Balancing (ELB) in Amazon Web Services (AWS) helps you in increasing the availability of applications with regular health checks and the distribution of traffic. It simply distributes the workload to numerous resources and increases the fault tolerance capacity of the applications. There are three types of elastic load balances which are classic load balancer (Clb), application load balancer (alb) and network load balancer (Nlb). Elb is very effective for companies as it increases the overall growth and traffic on your website. There are different interfaces like AWS management console, AWS command-line interface, Query API, etc which you can use for accessing, creating and managing your elastic load balancers.

AWS Elastic Load Balancing (ELB) is a service that automatically distributes incoming web traffic across multiple Amazon Elastic Compute Cloud (EC2) instances. ELB uses a variety of algorithms to route incoming traffic to the appropriate instances, such as round-robin and least connections.

List of few Pros/Cons of using AWS Elastic Load Balancer.

Pros

• Can handle the SSL termination, thus offloading the SSL processing from the instances.
• Provides health checks to ensure that only healthy instances receive traffic.
• Can be integrated with other AWS services such as Amazon CloudWatch for monitoring and Auto Scaling for automatic scaling of instances.

Cons

• Additional cost for using the service.
• May add latency to the requests as they pass through the load balancer.
• Limited control over the routing algorithm used by the load balancer.
• Can become a single point of failure if not configured with multiple availability zones.

ELB is responsible for directing traffic to the instances, while Auto Scaling is responsible for adjusting the number of instances to handle that traffic. Together, they provide a highly available and scalable infrastructure that can handle changes in traffic and adjust accordingly.

Load balancing techniques typically include:

• Round-robin: Requests are distributed evenly across servers
• IP hash: A hash function is used to determine which server a request should be sent to based on the client's IP address.
• URI-based: Requests are sent to different servers based on the URI of the request.
• Adaptive load balancing: The load balancer dynamically adjusts the algorithm it uses based on the current state of the servers.

Other techniques like weight round robin, least response time, etc.

In AWS, a target group is a group of resources that can receive traffic from an Application Load Balancer or a Network Load Balancer. Target groups are used to route traffic to specific resources based on the rules and settings defined in the load balancer. They can be used to perform health checks on the resources in the group, and only route traffic to healthy resources. They are associated with a load balancer and can be configured to route traffic to different resources based on the incoming request's protocol and host/path.

Amazon Route 53 and AWS Load Balancing serve different purposes, but both are used to manage and route incoming traffic to various resources.

Amazon's Route 53 is a DNS service that directs internet traffic to resources based on the domain name, while Load Balancing is a service that distributes incoming traffic across multiple resources within a single region.

An EC2 instance can only be associated with a single Elastic Load Balancer (ELB) at a time, whether it's an Application Load Balancer (ALB) or a Network Load Balancer (NLB). This means that you cannot use multiple ELBs to load balance traffic to a single EC2 instance.

AWS Elastic Load Balancers (ELBs) have more than one IP address for several reasons:

• High availability: Having multiple IP addresses allows the ELB to automatically failover to another IP address if one of them becomes unavailable. This ensures that traffic can still be routed to the load balancer even if one of the IP addresses goes down.
• Scaling: ELBs automatically scale to handle large amounts of traffic, and having multiple IP addresses allows them to handle more traffic by distributing it across multiple IP addresses.
• DDoS protection: Having multiple IP addresses can help protect against Distributed Denial of Service (DDoS) attacks. By distributing traffic across multiple IP addresses, an attacker would have to target multiple IP addresses to take down the load balancer.
• Performance: Having multiple IP addresses allows the load balancer to distribute traffic to different resources based on the incoming request's protocol and host/path. This can improve performance by directing traffic to the most appropriate resources.

It's worth noting that AWS Elastic Load Balancer IP addresses are not static and can change, so you should never hardcode the IP address of your ELB into your application. Instead, you should always use the DNS name of the ELB in your application, which will resolve to the correct IP addresses

AWS NLB is a type of load balancer that routes incoming traffic at the network level (OSI Layer 4) based on IP protocol data. It is designed for the handle millions of requests per second while maintaining ultra-low latencies.

NLBs are best suited for use cases that require high performance and scalability, such as handling requests for large-scale, distributed systems, and containerized microservices. The NLB uses a flow-hash algorithm to distribute incoming traffic across multiple resources and supports both TCP and UDP protocols.

There are multiple ways to create an alert for an out-of-service status for an AWS Load Balancer, but one possible method is to use Amazon CloudWatch Alarms.

• Here are the steps of the process:
• Open the Amazon CloudWatch console.
• In the navigation pane, choose Alarms, and then choose to Create alarm.
• In the Alarm details section, enter a name and description for the alarm.
• In the Alarm settings section, choose the LoadBalancer metric, and then choose the appropriate load balancer from the drop-down list.
• In the Conditions section, choose the OutOfService metric, and set the threshold for the alarm. This is the value that when crossed will trigger the alarm.
• In the Actions section, choose the SNS topic or any other action that you want to trigger when the alarm goes into the alarm state.

Once you have set up the alarm, it will monitor the status of your load balancer, and if the number of out-of-service instances exceeds the threshold you set, the alarm will trigger and take the specified actions.

The ELB (Elastic Load Balancer) has a non-configurable request timeout of 60 seconds because it is a default setting that is built into the ELB protocol. The ELB uses this timeout to ensure that it is able to quickly identify and close connections that are not being used.

This helps to prevent connection buildup and to ensure that resources are not being wasted on inactive connections. Additionally, the 60-second timeout allows the load balancer to quickly respond to changes in traffic patterns and to route traffic to the appropriate resource

Here is an overview of the process to create a VPC (Virtual Private Cloud) load balancer in AWS:

• Open the AWS Management Console and navigate to the Elastic Load Balancing service.
• Select "Create Load Balancer" and choose "Application Load Balancer" or "Network Load Balancer" according to your needs.
• In the "Configure Load Balancer" screen, provide a name for your load balancer and select the VPC in which you want to create it.
• In the "Configure Security Settings" screen, you can choose to create a new security group or use an existing one.
• In the "Configure Security Groups" screen, you can configure the security groups that you want to associate with your load balancer.
• In the "Configure Routing" screen, you can configure the routing settings for your load balancer.
• In the "Register Targets" screen, you can register the instances or IP addresses that you want to associate with your load balancer.
• In the "Review" screen, review your settings and then choose "Create" to create your VPC load balancer.

Once your VPC load balancer is created, you can configure the listener, health check, and target group accordingly.

VPC load balancer or Virtual Private Cloud load balancer is used to assign security groups to your VPC and offers the ability to load balance across the network and the platforms.