Auto Scaling with ELB integration in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of Auto Scaling in AWS?

Auto Scaling automatically adjusts the number of running instances to match the current demand, helping maintain performance and control costs.

beginner

How does Elastic Load Balancer (ELB) work with Auto Scaling?

ELB distributes incoming traffic evenly across all healthy instances in the Auto Scaling group, ensuring no single instance is overwhelmed.

intermediate

What happens when a new instance is launched by Auto Scaling in an ELB-integrated setup?

The new instance is automatically registered with the ELB, so it starts receiving traffic once it passes health checks.

intermediate

Why is health checking important in Auto Scaling with ELB?

Health checks help ELB and Auto Scaling detect unhealthy instances and replace them, maintaining application availability and reliability.

advanced

What is a best practice when configuring Auto Scaling with ELB?

Use ELB health checks combined with Auto Scaling group health checks to ensure instances are only serving traffic when fully ready.

What does Auto Scaling do when traffic increases?

A Disables the ELB

B Launches more instances to handle the load

C Sends traffic to a single instance

D Shuts down instances to save cost

Auto Scaling launches more instances to handle increased traffic and maintain performance.

How does ELB decide which instances to send traffic to?

A Only to the newest instance

B Only to instances with the lowest CPU usage

C Randomly to any instance

D Evenly across all healthy instances

ELB distributes traffic evenly across all instances that pass health checks.

What happens if an instance fails ELB health checks?

A It continues to receive traffic

B The ELB shuts down

C It is removed from the ELB and replaced by Auto Scaling

D Traffic is redirected to the failing instance

Failing instances are removed from ELB and Auto Scaling can replace them to keep the application healthy.

Which AWS service automatically registers new instances with ELB?

A Auto Scaling

B Amazon S3

C AWS Lambda

D Amazon RDS

Auto Scaling automatically registers new instances with the ELB when they launch.

What is a key benefit of integrating Auto Scaling with ELB?

A Automatic traffic distribution and scaling

B Static number of instances

C Manual traffic routing

D No health checks needed

Integration allows automatic scaling and balanced traffic distribution for better availability.

Explain how Auto Scaling and ELB work together to maintain application availability.

Think about how traffic and instance health are managed automatically.

Describe the role of health checks in Auto Scaling with ELB integration.

Consider why it is important to know if an instance is working well.

Practice

1. What is the main purpose of integrating an Auto Scaling group with an Elastic Load Balancer (ELB)?

easy

A. To distribute incoming traffic evenly across all running instances

B. To store data persistently across instances

C. To create backups of instances automatically

D. To monitor the health of the database

Solution

1. Step 1: Understand Auto Scaling and ELB roles

   Auto Scaling adjusts the number of servers based on demand. ELB distributes user traffic across these servers.

2. Step 2: Identify integration benefit

   Linking Auto Scaling with ELB ensures traffic is balanced only to healthy, running instances, improving availability.

3. Final Answer:

   To distribute incoming traffic evenly across all running instances -> Option A

4. Quick Check:

   Auto Scaling + ELB = balanced traffic [OK]

Hint: ELB balances traffic; Auto Scaling adjusts servers [OK]

Common Mistakes:

• Confusing ELB with storage or backup services
• Thinking Auto Scaling manages data persistence
• Assuming ELB monitors databases

2. Which of the following is the correct way to attach an Auto Scaling group to an ELB target group in AWS CLI?

easy

A. aws elb attach-instances --group-name my-asg --target-group-arn arn:aws:elasticloadbalancing:region:123456789012:targetgroup/my-target-group/abcdef123456

B. aws elb create-auto-scaling-group --name my-asg --target-group my-target-group

C. aws autoscaling create-target-group --name my-target-group --auto-scaling-group my-asg

D. aws autoscaling attach-load-balancer-target-groups --auto-scaling-group-name my-asg --target-group-arns arn:aws:elasticloadbalancing:region:123456789012:targetgroup/my-target-group/abcdef123456

Solution

1. Step 1: Identify correct AWS CLI command

   The command to attach an Auto Scaling group to an ELB target group is 'aws autoscaling attach-load-balancer-target-groups'.

2. Step 2: Verify command parameters

   It requires the Auto Scaling group name and the target group ARN, matching aws autoscaling attach-load-balancer-target-groups --auto-scaling-group-name my-asg --target-group-arns arn:aws:elasticloadbalancing:region:123456789012:targetgroup/my-target-group/abcdef123456.

3. Final Answer:

   aws autoscaling attach-load-balancer-target-groups --auto-scaling-group-name my-asg --target-group-arns arn:aws:elasticloadbalancing:region:123456789012:targetgroup/my-target-group/abcdef123456 -> Option D

4. Quick Check:

   Attach ASG to ELB target group uses attach-load-balancer-target-groups [OK]

Hint: Use 'attach-load-balancer-target-groups' with ASG name and target group ARN [OK]

Common Mistakes:

• Using ELB commands instead of Auto Scaling commands
• Confusing target group ARN with target group name
• Trying to create target groups via Auto Scaling CLI

3. Given this AWS Auto Scaling group configuration snippet:

{
  "AutoScalingGroupName": "web-asg",
  "TargetGroupARNs": ["arn:aws:elasticloadbalancing:region:123456789012:targetgroup/web-tg/abc123"],
  "MinSize": 2,
  "MaxSize": 4,
  "DesiredCapacity": 3
}

What happens when one instance fails health checks in the ELB target group?

medium

A. Auto Scaling terminates the unhealthy instance and launches a new one to maintain desired capacity

B. ELB stops sending traffic but Auto Scaling does not replace the instance

C. Auto Scaling increases MaxSize to 5 automatically

D. Nothing happens until manual intervention

Solution

1. Step 1: Understand health check integration

   When an instance fails ELB health checks, Auto Scaling detects it as unhealthy.

2. Step 2: Auto Scaling response

   Auto Scaling terminates the unhealthy instance and launches a new one to keep the desired capacity at 3.

3. Final Answer:

   Auto Scaling terminates the unhealthy instance and launches a new one to maintain desired capacity -> Option A

4. Quick Check:

   Unhealthy instance triggers replacement by Auto Scaling [OK]

Hint: Auto Scaling replaces unhealthy instances to keep desired capacity [OK]

Common Mistakes:

• Thinking ELB alone replaces instances
• Assuming MaxSize changes automatically
• Believing manual steps are needed

4. You configured an Auto Scaling group with an ELB target group, but new instances are not receiving traffic. What is the most likely cause?

medium

A. The ELB is in a different AWS region than the Auto Scaling group

B. The Auto Scaling group has MinSize set to zero

C. The instances are not registered with the ELB target group

D. The instances do not have public IP addresses

Solution

1. Step 1: Check ELB and Auto Scaling integration

   If instances are not registered with the ELB target group, ELB cannot send traffic to them.

2. Step 2: Evaluate other options

   MinSize zero means no instances; region mismatch prevents communication; public IP not required for ELB internal routing.

3. Final Answer:

   The instances are not registered with the ELB target group -> Option C

4. Quick Check:

   Instances must be registered with ELB target group to get traffic [OK]

Hint: Check instance registration in ELB target group first [OK]

Common Mistakes:

• Assuming public IP is required for ELB traffic
• Ignoring instance registration status
• Confusing region mismatch with availability zone issues

5. You want to ensure your Auto Scaling group scales out only when the average CPU usage across all instances exceeds 70%, and also that new instances are healthy in the ELB before receiving traffic. Which combination of settings achieves this?

hard

A. Configure scaling policy on network traffic, and skip ELB health checks

B. Create a scaling policy based on CPU > 70%, enable ELB health checks with grace period

C. Use ELB health checks only, no CPU-based scaling policy

D. Set MinSize to 0, MaxSize to 10, and disable ELB health checks

Solution

1. Step 1: Define scaling trigger

   Scaling based on average CPU > 70% ensures scale out matches demand.

2. Step 2: Ensure instance health before traffic

   Enabling ELB health checks with a grace period lets new instances become healthy before receiving traffic.

3. Step 3: Combine both for smooth scaling

   This combination prevents traffic to unhealthy instances and scales only when needed.

4. Final Answer:

   Create a scaling policy based on CPU > 70%, enable ELB health checks with grace period -> Option B

5. Quick Check:

   CPU scaling + ELB health checks = safe, demand-based scaling [OK]

Hint: Combine CPU scaling policy with ELB health checks and grace period [OK]

Common Mistakes:

• Disabling ELB health checks causing traffic to unhealthy instances
• Using wrong metric like network traffic for CPU-based scaling
• Not setting grace period causing premature traffic routing