Auto Scaling groups in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

How does an Auto Scaling group handle instance health checks?

An Auto Scaling group monitors the health of its instances. What happens when an instance fails a health check?

A The instance is terminated and replaced with a new one automatically.

B The instance is rebooted but not replaced.

C The instance is left running but marked unhealthy in the console.

D The Auto Scaling group pauses scaling activities until manual intervention.

💡 Hint

Think about how Auto Scaling keeps your application healthy without manual work.

Auto Scaling groups automatically terminate unhealthy instances and launch new ones to maintain the desired capacity and health of your application.

❓ Architecture

intermediate

What is the effect of setting the minimum size to 3 and maximum size to 5 in an Auto Scaling group?

You configure an Auto Scaling group with a minimum size of 3 and a maximum size of 5. What does this configuration guarantee?

A The group will launch exactly 4 instances at all times.

B The group will always have at least 3 instances and never more than 5 instances running.

C The group can scale down to zero instances if demand is low.

D The group will launch 5 instances immediately and never scale down.

💡 Hint

Minimum and maximum sizes define the boundaries for scaling.

The minimum size ensures the group never has fewer than 3 instances, and the maximum size prevents it from exceeding 5 instances.

❓ security

advanced

Which IAM permission is required to allow an Auto Scaling group to launch EC2 instances?

To enable an Auto Scaling group to launch EC2 instances, which IAM permission must be granted to the Auto Scaling service role?

A autoscaling:UpdateAutoScalingGroup

B autoscaling:CreateLaunchConfiguration

C ec2:RunInstances

D ec2:TerminateInstances

💡 Hint

Launching instances requires permission to start EC2 instances.

The Auto Scaling service role needs the ec2:RunInstances permission to launch new EC2 instances as part of scaling activities.

❓ Configuration

advanced

What happens if you set the desired capacity higher than the maximum size in an Auto Scaling group?

You configure an Auto Scaling group with a desired capacity of 6 but set the maximum size to 5. What will be the actual number of instances running?

A The group will launch 1 instance and wait for manual scaling.

B The group will launch 6 instances, ignoring the maximum size.

C The group will launch 0 instances due to configuration conflict.

D The group will launch 5 instances, respecting the maximum size limit.

💡 Hint

Maximum size limits the upper bound of instances regardless of desired capacity.

The Auto Scaling group enforces the maximum size limit and will not launch more than 5 instances even if desired capacity is set higher.

✅ Best Practice

expert

Which strategy best ensures zero downtime during Auto Scaling group instance replacement?

You want to replace instances in an Auto Scaling group without causing downtime. Which approach achieves this?

A Use rolling updates with a health check grace period and minimum healthy percentage set above 50%.

B Terminate all instances at once and then launch new ones immediately.

C Manually stop instances one by one without updating the Auto Scaling group.

D Set desired capacity to zero before launching new instances.

💡 Hint

Think about how to keep enough healthy instances running during updates.

Rolling updates with a health check grace period and a minimum healthy percentage ensure new instances are healthy before old ones are terminated, preventing downtime.

Practice

1. What is the main purpose of an Auto Scaling group in AWS?

easy

A. To store data in a scalable database

B. To manage user access and permissions

C. To automatically adjust the number of servers based on demand

D. To monitor network traffic for security threats

Solution

1. Step 1: Understand Auto Scaling group function

   An Auto Scaling group automatically changes the number of servers to match demand.

2. Step 2: Compare options to this function

   Only To automatically adjust the number of servers based on demand describes automatic adjustment of servers based on demand.

3. Final Answer:

   To automatically adjust the number of servers based on demand -> Option C

4. Quick Check:

   Auto Scaling = Adjust servers automatically [OK]

Hint: Auto Scaling groups adjust servers automatically [OK]

Common Mistakes:

• Confusing Auto Scaling with database services
• Thinking Auto Scaling manages user permissions
• Assuming Auto Scaling monitors security

2. Which of the following is the correct way to set the minimum size of an Auto Scaling group using AWS CLI?

easy

A. aws autoscaling set-minimum --group my-asg --size 2

B. aws autoscaling update-auto-scaling-group --auto-scaling-group-name my-asg --min-size 2

C. aws autoscaling create-auto-scaling-group --min 2 --name my-asg

D. aws autoscaling configure-group --asg my-asg --minimum 2

Solution

1. Step 1: Recall AWS CLI command for updating Auto Scaling group

   The correct command to update settings is 'update-auto-scaling-group' with parameters for group name and min size.

2. Step 2: Check each option's syntax

   aws autoscaling update-auto-scaling-group --auto-scaling-group-name my-asg --min-size 2 uses correct command and parameters. Others use invalid commands or parameters.

3. Final Answer:

   aws autoscaling update-auto-scaling-group --auto-scaling-group-name my-asg --min-size 2 -> Option B

4. Quick Check:

   Update Auto Scaling group with correct CLI syntax [OK]

Hint: Use 'update-auto-scaling-group' to change min size [OK]

Common Mistakes:

• Using create command instead of update
• Wrong parameter names like --min or --minimum
• Incorrect command verbs like set-minimum or configure-group

3. Given this Auto Scaling group configuration:
MinSize=1, MaxSize=3, DesiredCapacity=2
What happens if the load increases and the group scales out to 3 instances, then the load drops suddenly?

medium

A. The group will scale in to 1 instance, respecting MinSize

B. The group will keep 3 instances running regardless of load

C. The group will scale in to 0 instances

D. The group will scale in to 2 instances, the DesiredCapacity

Solution

1. Step 1: Understand scaling limits

   MinSize=1 means the group will never go below 1 instance, MaxSize=3 means it can scale up to 3.

2. Step 2: Analyze behavior on load drop

   When load drops, Auto Scaling reduces instances but not below MinSize, so it scales down to 1.

3. Final Answer:

   The group will scale in to 1 instance, respecting MinSize -> Option A

4. Quick Check:

   MinSize limits minimum instances [OK]

Hint: MinSize sets the lowest number of instances [OK]

Common Mistakes:

• Thinking DesiredCapacity is fixed after scaling
• Assuming scaling can go below MinSize
• Believing MaxSize limits minimum instances

4. You wrote this snippet to create an Auto Scaling group but it fails:

aws autoscaling create-auto-scaling-group --auto-scaling-group-name my-asg --min-size 2 --max-size 1 --desired-capacity 1 --launch-configuration-name my-launch-config --vpc-zone-identifier subnet-12345

What is the error?

medium

A. VPC subnet ID is invalid

B. DesiredCapacity cannot be less than MinSize

C. Launch configuration name is missing

D. MinSize cannot be greater than MaxSize

Solution

1. Step 1: Check size parameters

   MinSize is set to 2, MaxSize is set to 1, which is invalid because MinSize must be less than or equal to MaxSize.

2. Step 2: Validate other parameters

   DesiredCapacity is 1, which is allowed if between MinSize and MaxSize, but here MinSize > MaxSize causes failure.

3. Final Answer:

   MinSize cannot be greater than MaxSize -> Option D

4. Quick Check:

   MinSize ≤ MaxSize rule violated [OK]

Hint: MinSize must be ≤ MaxSize to create group [OK]

Common Mistakes:

• Setting MinSize higher than MaxSize
• Ignoring error messages about sizes
• Assuming DesiredCapacity fixes size conflicts

5. You want an Auto Scaling group that maintains at least 2 instances, scales up to 5 during high load, and automatically replaces unhealthy instances. Which configuration achieves this?

hard

A. Set MinSize=2, MaxSize=5, DesiredCapacity=2, enable health checks and instance replacement

B. Set MinSize=5, MaxSize=2, DesiredCapacity=3, disable health checks

C. Set MinSize=0, MaxSize=5, DesiredCapacity=5, no health checks

D. Set MinSize=2, MaxSize=5, DesiredCapacity=5, disable instance replacement

Solution

1. Step 1: Define scaling limits

   MinSize=2 ensures at least 2 instances, MaxSize=5 allows scaling up to 5.

2. Step 2: Set desired capacity and health checks

   DesiredCapacity=2 starts with 2 instances. Enabling health checks and instance replacement ensures unhealthy instances are replaced automatically.

3. Step 3: Evaluate other options

   The other options either have invalid MinSize/MaxSize, disable health checks, or disable instance replacement.

4. Final Answer:

   Set MinSize=2, MaxSize=5, DesiredCapacity=2, enable health checks and instance replacement -> Option A

5. Quick Check:

   Correct scaling limits and health checks enabled [OK]

Hint: MinSize ≤ DesiredCapacity ≤ MaxSize with health checks enabled [OK]

Common Mistakes:

• Setting MinSize greater than MaxSize
• Disabling health checks or instance replacement
• Setting DesiredCapacity outside Min/Max range