Elastic Load Balancing Algorithms

5 minutes 5 Questions

Elastic Load Balancing Algorithms determine how the load balancer distributes incoming traffic across the registered instances. AWS supports two types of load balancing algorithms: 1. Round Robin: This is a default method, where each instance gets an equal distribution of traffic, ensuring balanced…

Guide to Elastic Load Balancing Algorithms

Elastic Load Balancing Algorithms (ELB Algorithms) are crucial components in the AWS architecture.

Importance: ELB Algorithms play a fundamental role in distributing incoming application or network traffic across multiple targets, such as Amazon EC2 instances. This ensures the smooth functioning of applications by providing fault tolerance so that any single point of failure can be handled with minimal service disruption.
What it is: ELB Algorithms are part of the AWS Elastic Load Balancing service. They decide how to distribute incoming requests to targets based on factors such as the current load on individual targets. The choice of algorithm depends on your specific needs. AWS provides several types of load balancing algorithms such as round robin, least outstanding requests, and IP hash.
How it works: Based on the selected algorithm, the ELB evaluates the condition of targets and forwards incoming requests accordingly. For instance, the round robin method distributes requests evenly, while the least outstanding requests method prioritizes targets with fewest pending requests.
Exam Tips: When it comes to answering questions regarding ELB Algorithms on an exam, remember to:
- Understand how different types of algorithms work and when to use which type.
- Be aware of the comparison between various algorithms in terms of efficiency, speed, and demands.
- Have practical insights about real-world scenarios where certain algorithms are more suited.

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AWS Certified Solutions Architect - Elastic Load Balancing Algorithms Example Questions

Test your knowledge of Elastic Load Balancing Algorithms

Question 1

In AWS, an Application Load Balancer is distributing HTTP(S) traffic to a homogeneous fleet of targets. During peak traffic, users see higher response times due to request queuing at busy targets. Which load-balancing algorithm should be selected to minimize per-request latency by routing new requests to the least busy target?

Least Connections Weighted Round Robin Least Outstanding Requests Round Robin

Correct Answer: Least Outstanding Requests

For AWS Application Load Balancer handling HTTP/HTTPS traffic, the Least Outstanding Requests algorithm routes each new request to the target with the fewest in-flight requests, directly reducing queueing time and improving both average and tail latency under peak load. Round Robin spreads traffic evenly but ignores current load, Least Connections focuses on open connections rather than active request backlog (which can mislead with keep-alives and varying request times), and Weighted Round Robin is used for shifting traffic between target groups rather than minimizing per-target latency.

Question 2

A media streaming platform delivers HLS/DASH video over HTTPS and uses Amazon CloudFront for global edge delivery. In each AWS Region, it needs a load balancer that terminates HTTPS, performs path/host-based routing to separate microservices (such as video origin, authentication, and API), and supports canary or blue/green deployments by sending traffic to different sets of targets. Which Elastic Load Balancer configuration best fits these requirements?

Application Load Balancer with single target group Network Load Balancer with multiple target groups Application Load Balancer with multiple target groups Classic Load Balancer with single target group

Correct Answer: Application Load Balancer with multiple target groups

An Application Load Balancer (ALB) operates at Layer 7 and supports host/path-based routing, header-based rules, and forwarding to multiple target groups with weights. For HTTP-based HLS/DASH video over HTTPS behind a global CDN like CloudFront, an ALB can terminate TLS and route requests to distinct microservices (e.g., video origin, auth, API) and support canary or blue/green by directing traffic to multiple target groups per listener rule. A Network Load Balancer is Layer 4 and cannot perform content-based routing; Classic Load Balancer is legacy and lacks advanced L7 features; an ALB with a single target group would not meet the requirement to route to different services and canary targets.

Question 3

You host a game lobby over HTTPS where clients connect via HTTP(S)/WebSocket to a single load balancer endpoint. Each request includes a region code in the URL path (for example, /region/eu or /region/na). You maintain separate target groups for each region and need the load balancer to route requests to the correct target group based on the path. Which Elastic Load Balancer configuration should you use?

Application Load Balancer with rule-based routing Network Load Balancer with protocol-based routing Classic Load Balancer with IP-based routing Classic Load Balancer with regional routing

Correct Answer: Application Load Balancer with rule-based routing

An Application Load Balancer (ALB) operates at Layer 7 and supports rule-based routing using HTTP request attributes such as host, path, and headers. It also supports WebSocket over HTTP(S). In this scenario, ALB path-based rules can route requests like /region/eu or /region/na to the corresponding target groups. A Network Load Balancer is Layer 4 and cannot inspect URL paths, and Classic Load Balancer lacks modern rule-based routing features and does not provide geographic or IP-based content routing.

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