Cross-zone load balancing in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Cross-Zone Load Balancing Behavior

What is the main effect of enabling cross-zone load balancing on an AWS Application Load Balancer?

A It disables health checks for targets in other Availability Zones.

B It restricts traffic to targets only within the same Availability Zone as the load balancer node.

C It evenly distributes incoming traffic across all registered targets in all enabled Availability Zones.

D It routes all traffic to the target group with the lowest latency regardless of zone.

💡 Hint

Think about how traffic is balanced when targets are unevenly distributed across zones.

Enabling cross-zone load balancing allows the load balancer to distribute traffic evenly across all registered targets in all zones, preventing uneven load when targets are not evenly spread.

❓ Architecture

intermediate

Designing for High Availability with Cross-Zone Load Balancing

You have an AWS Network Load Balancer with targets unevenly distributed: 3 targets in Zone A and 1 target in Zone B. Cross-zone load balancing is disabled. What is the expected traffic distribution?

A Traffic is split evenly between Zone A and Zone B, but Zone B targets get more traffic per instance.

B Traffic is split evenly between all targets regardless of zone.

C Traffic is routed only to Zone B targets.

D All traffic is routed only to Zone A targets.

💡 Hint

Consider how load balancers distribute traffic when cross-zone load balancing is off and targets are uneven.

With cross-zone load balancing off, the load balancer distributes traffic evenly across Availability Zones, not targets. Zone B has fewer targets, so each target there receives more traffic.

❓ Configuration

advanced

Enabling Cross-Zone Load Balancing via AWS CLI

Which AWS CLI command correctly enables cross-zone load balancing for a Network Load Balancer named my-nlb?

AWS

aws elbv2 modify-load-balancer-attributes --load-balancer-arn <load-balancer-arn> --attributes Key=load_balancing.cross_zone.enabled,Value=true

A aws elbv2 modify-load-balancer-attributes --load-balancer-arn <load-balancer-arn> --attributes Key=load_balancing.cross_zone.enabled,Value=true

B aws elbv2 set-load-balancer-attributes --name my-nlb --cross-zone-load-balancing enabled

C aws elbv2 update-load-balancer --name my-nlb --cross-zone true

D aws elbv2 enable-cross-zone --load-balancer-name my-nlb

💡 Hint

Look for the correct AWS CLI command and attribute syntax for modifying load balancer attributes.

The correct command uses modify-load-balancer-attributes with the attribute key load_balancing.cross_zone.enabled set to true.

❓ security

advanced

Security Implications of Cross-Zone Load Balancing

What is a potential security consideration when enabling cross-zone load balancing on an AWS load balancer?

A It disables encryption between the load balancer and targets.

B It may increase inter-AZ data transfer costs and expose traffic to more network paths, increasing attack surface.

C It automatically opens all inbound ports on targets for cross-zone traffic.

D It disables AWS WAF protections on the load balancer.

💡 Hint

Think about how traffic flows between zones and what that means for security and costs.

Cross-zone load balancing causes traffic to flow between Availability Zones, which can increase data transfer costs and expose traffic to more network paths, potentially increasing the attack surface.

❓ service_behavior

expert

Impact of Cross-Zone Load Balancing on Auto Scaling Behavior

You have an Auto Scaling group behind an Application Load Balancer with cross-zone load balancing enabled. If one Availability Zone loses all its instances, what happens to the traffic distribution?

A Traffic to the affected zone is dropped until instances are replaced manually.

B The load balancer disables cross-zone load balancing automatically.

C The load balancer continues to send traffic evenly to all zones, causing errors in the empty zone.

D The load balancer automatically routes all traffic to instances in the remaining zones without manual intervention.

💡 Hint

Consider how the load balancer handles target health and zone availability.

With cross-zone load balancing enabled, the load balancer detects unhealthy or missing targets in a zone and routes traffic to healthy targets in other zones automatically.