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Cross-Zone Load Balancing

5 minutes 5 Questions

Cross-Zone Load Balancing is an essential concept to ensure high availability and fault tolerance of your application deployed across multiple Availability Zones. By enabling Cross-Zone Load Balancing, the traffic is distributed evenly not just among instances in a single Availability Zone but across all registered instances in multiple Availability Zones. This helps you achieve better resource utilization, high availability, and consistent performance for your applications. In addition, it prevents service disruptions and uneven distribution of traffic due to issues in a single Availability Zone, ensuring that your application continues to run smoothly even during an outage in one of the zones.

Guide: Cross-Zone Load Balancing in AWS

Cross-Zone Load Balancing(ELB) is a vital feature of AWS. It is of major importance in maintaining high availability and fault tolerance of applications. By distributing traffic evenly across all registered instances in its enabled Availability Zones, it provides better fault tolerance. This ensures that your application is not affected even if a few instances are unhealthy.

What is Cross-Zone Load Balancing?
It is a method that allows the load balancer to distribute traffic equally across all registered instances in all enabled Availability Zones, not just the one where the request was initially directed.

How does it work?
Whenever your load balancer receives a request, it routes the request to the backend instance with the smallest load in any Availability Zone. This is determined by Connection Draining, a process from the Elastic Load Balancing feature.

Exam Tips: Answering Questions on Cross-Zone Load Balancing
1. Understanding: Understand the basic working of Cross-Zone Load balancing. Know that it does not restrict traffic to the same zone. Traffic is distributed evenly across instances in all zones.
2. Comparisons: Be able to compare Cross-Zone with single-zone load balancing. Know the differences clearly and when to use each.
3. Enable/Disable: Know how to enable and disable the feature, and the situations where you would want to do so.
4. Costs: Understand the costs that apply when Cross-Zone load balancing is enabled.
5. Key Features: Be aware of key features - such as Connection Draining and Sticky Sessions that are associated with ELB and can be related to questions on Cross-Zone load balancing.

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AWS Certified Solutions Architect - Elastic Load Balancing (ELB) Example Questions

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Question 1

You have an Application Load Balancer configured for cross-zone load balancing. One of the target groups is misconfigured, causing a disruption in performance. How would you resolve this?

Correct Answer: Fix the misconfiguration in the target group and verify that the load balancer can access targets in multiple Availability Zones

The correct way to resolve this issue is by fixing the misconfiguration in the target group and then verifying that the load balancer is able to access targets in multiple Availability Zones. Changing to Network Load Balancer, enabling Route 53 routing, enabling instance stickiness or Direct Connect will not address the issue of a misconfigured target group.

Question 2

You are seeing uneven workload distribution between instances within the same Availability Zone due to a Network Load Balancer. What should you do?

Correct Answer: Enable cross-zone load balancing on the Network Load Balancer

Enabling cross-zone load balancing on the Network Load Balancer allows for the load to be distributed evenly across all instances within different Availability Zones. Application Load Balancer or Classic Load Balancer will not solve the issue since they handle different types of traffic. Route 53 latency-based routing is not related to cross-zone load balancing. Auto Scaling and Placement Groups are not relevant here, as they don't address the uneven workload distribution issue.

Question 3

Your application has an evenly distributed traffic across multiple instances within an Availability Zone, but users of one Availability Zone experience slow response times. What would you recommend?

Correct Answer: Enable cross-zone load balancing on your load balancer

Enabling cross-zone load balancing will distribute the traffic evenly across instances in different Availability Zones. Direct Connect is for connecting on-premise environments to AWS, while VPNs help in connecting separate VPCs. The problem is within the same VPC, so these are not applicable. Route 53 latency-based routing will not distribute the traffic between Availability Zones under the same region, and changing the Load Balancer type will not address the uneven traffic distribution.

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