Cross-zone load balancing in AWS - Mini Project: Build & Apply

Enable Cross-Zone Load Balancing on an AWS Application Load Balancer

📖 Scenario: You are managing a web application hosted on AWS. To improve availability and distribute traffic evenly, you use an Application Load Balancer (ALB) across multiple Availability Zones.By default, the ALB routes traffic to targets in the same zone as the request. To optimize traffic distribution, you want to enable cross-zone load balancing.

🎯 Goal: Configure an AWS Application Load Balancer to enable cross-zone load balancing using AWS CLI commands.

📋 What You'll Learn

Create an Application Load Balancer named my-alb in two Availability Zones

Create a target group named my-target-group

Register two targets with the target group

Enable cross-zone load balancing on the Application Load Balancer

💡 Why This Matters

🌍 Real World

Cross-zone load balancing helps distribute incoming traffic evenly across multiple Availability Zones, improving application availability and fault tolerance.

💼 Career

Cloud architects and DevOps engineers often configure load balancers with cross-zone load balancing to optimize resource utilization and ensure high availability.

1

Create the Application Load Balancer

Use the AWS CLI command to create an Application Load Balancer named my-alb in the subnets subnet-123abc and subnet-456def. Include the security group sg-789xyz, specify the type as application, and specify the scheme as internet-facing.

AWS

# Use aws elbv2 create-load-balancer command with the specified name, subnets, security groups, type, and scheme
# Your code here

Hint

Use the aws elbv2 create-load-balancer command with the required parameters.

2

Create the Target Group

Create a target group named my-target-group for instances using the protocol HTTP and port 80. Use the VPC ID vpc-abc123.

AWS

aws elbv2 create-load-balancer --name my-alb --type application --subnets subnet-123abc subnet-456def --security-groups sg-789xyz --scheme internet-facing
# Use aws elbv2 create-target-group command with the specified name, protocol, port, and VPC ID
# Your code here

Hint

Use the aws elbv2 create-target-group command with the required parameters.

3

Register Targets with the Target Group

Register two instance targets with IDs i-0123456789abcdef0 and i-0fedcba9876543210 to the target group named my-target-group on port 80.

AWS

aws elbv2 create-load-balancer --name my-alb --type application --subnets subnet-123abc subnet-456def --security-groups sg-789xyz --scheme internet-facing
aws elbv2 create-target-group --name my-target-group --protocol HTTP --port 80 --vpc-id vpc-abc123
# Use aws elbv2 register-targets command to add the two instances to my-target-group
# Your code here

Hint

Use the aws elbv2 register-targets command with the target group ARN and target instance IDs.

4

Enable Cross-Zone Load Balancing

Enable cross-zone load balancing on the Application Load Balancer named my-alb by modifying its attributes using the AWS CLI.

AWS

aws elbv2 create-load-balancer --name my-alb --type application --subnets subnet-123abc subnet-456def --security-groups sg-789xyz --scheme internet-facing
aws elbv2 create-target-group --name my-target-group --protocol HTTP --port 80 --vpc-id vpc-abc123
aws elbv2 register-targets --target-group-arn arn:aws:elasticloadbalancing:region:account-id:targetgroup/my-target-group/1234567890abcdef --targets Id=i-0123456789abcdef0 Id=i-0fedcba9876543210
# Use aws elbv2 modify-load-balancer-attributes to enable cross-zone load balancing for my-alb
# Your code here

Hint

Use the aws elbv2 modify-load-balancer-attributes command with the correct attribute key and value.

Practice

1. What is the main benefit of enabling cross-zone load balancing in AWS Elastic Load Balancer?

easy

A. It increases the maximum number of connections per target.

B. It automatically scales the number of Availability Zones.

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

D. It encrypts all traffic between the load balancer and targets.

Solution

1. Step 1: Understand cross-zone load balancing purpose

   Cross-zone load balancing spreads traffic evenly across targets in all zones, preventing uneven load.

2. Step 2: Compare options to this purpose

   Only It evenly distributes incoming traffic across all registered targets in all enabled Availability Zones. describes this even distribution. Other options describe unrelated features.

3. Final Answer:

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

4. Quick Check:

   Cross-zone load balancing = even traffic spread [OK]

Hint: Cross-zone means traffic spreads evenly across zones [OK]

Common Mistakes:

• Confusing cross-zone with encryption or scaling
• Thinking it increases max connections per target
• Assuming it changes number of zones automatically

2. Which of the following is the correct way to enable cross-zone load balancing in an AWS Application Load Balancer using Terraform?

easy

A. enable_cross_zone_load_balancing = false

B. cross_zone_load_balancing = true

C. cross_zone_enabled = true

D. enable_cross_zone_load_balancing = true

Solution

1. Step 1: Recall Terraform attribute for cross-zone load balancing

   The correct attribute is enable_cross_zone_load_balancing and it must be set to true to enable.

2. Step 2: Match options to correct syntax

   Only enable_cross_zone_load_balancing = true uses the exact attribute name and sets it to true.

3. Final Answer:

   enable_cross_zone_load_balancing = true -> Option D

4. Quick Check:

   Terraform attribute = enable_cross_zone_load_balancing true [OK]

Hint: Look for exact attribute name with true value [OK]

Common Mistakes:

• Using incorrect attribute names like cross_zone_load_balancing
• Setting the value to false instead of true
• Confusing with other unrelated settings

3. Given the following AWS CLI command to enable cross-zone load balancing on a Classic Load Balancer:

aws elb modify-load-balancer-attributes --load-balancer-name my-load-balancer --load-balancer-attributes '{"CrossZoneLoadBalancing":{"Enabled":true}}'

What will be the effect of running this command?

medium

A. Cross-zone load balancing will be disabled for the load balancer.

B. Cross-zone load balancing will be enabled, distributing traffic evenly across zones.

C. The load balancer will be deleted.

D. The command will fail due to syntax error.

Solution

1. Step 1: Analyze the AWS CLI command structure

   The command modifies load balancer attributes, specifically enabling CrossZoneLoadBalancing by setting Enabled to true.

2. Step 2: Understand the effect of enabling CrossZoneLoadBalancing

   Enabling it causes traffic to be evenly distributed across all registered targets in all zones.

3. Final Answer:

   Cross-zone load balancing will be enabled, distributing traffic evenly across zones. -> Option B

4. Quick Check:

   Enable CrossZoneLoadBalancing true = even traffic spread [OK]

Hint: Enabled true means cross-zone load balancing is active [OK]

Common Mistakes:

• Thinking the command disables the feature
• Assuming the load balancer is deleted
• Believing the command syntax is incorrect

4. You configured cross-zone load balancing on your Network Load Balancer but notice traffic is still uneven across zones. What is the most likely cause?

medium

A. You forgot to register targets in all Availability Zones.

B. Cross-zone load balancing is not supported on Network Load Balancers.

C. Cross-zone load balancing requires manual DNS updates.

D. You must enable cross-zone load balancing on each target instance.

Solution

1. Step 1: Recall cross-zone load balancing support on Network Load Balancers

   Network Load Balancers support cross-zone load balancing, but it must be enabled and targets must be registered in all zones.

2. Step 2: Identify why traffic is uneven

   If targets are missing in some zones, traffic cannot be balanced evenly despite cross-zone load balancing being enabled.

3. Final Answer:

   You forgot to register targets in all Availability Zones. -> Option A

4. Quick Check:

   Targets missing in zones = uneven traffic [OK]

Hint: Ensure targets exist in all zones for balancing [OK]

Common Mistakes:

• Thinking cross-zone load balancing is unsupported on NLB
• Believing DNS updates are needed
• Assuming enabling on targets is required

5. You have an Application Load Balancer spanning three Availability Zones with cross-zone load balancing enabled. One zone has only one healthy target, while the others have three each. How does cross-zone load balancing affect traffic distribution?

hard

A. Traffic is evenly distributed across all targets regardless of zone count.

B. Traffic is evenly distributed across zones, so the zone with one target gets one-third of traffic.

C. Traffic is sent only to zones with the most targets.

D. Traffic is distributed randomly without considering zones or targets.

Solution

1. Step 1: Understand cross-zone load balancing behavior

   With cross-zone load balancing enabled, each load balancer node distributes traffic evenly across all healthy registered targets, regardless of their Availability Zone.

2. Step 2: Apply to given scenario

   Total healthy targets: 1 + 3 + 3 = 7. Each target receives approximately equal traffic (1/7), so the zone with one target gets about 1/7 of total traffic.

3. Final Answer:

   Traffic is evenly distributed across all targets regardless of zone count. -> Option A

4. Quick Check:

   Cross-zone load balancing = even across all targets [OK]

Hint: Cross-zone balances evenly across all targets, ignoring zone boundaries [OK]

Common Mistakes:

• Confusing with default zone-isolated balancing (even per zone)
• Thinking traffic prefers zones with more targets
• Believing distribution ignores target count