Alarm actions (SNS, Auto Scaling) in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

What happens when a CloudWatch alarm triggers an SNS notification?

You have a CloudWatch alarm configured to send a notification to an SNS topic when CPU usage exceeds 80%. What is the expected behavior when the alarm state changes to ALARM?

A The SNS topic sends the notification message to all its subscribed endpoints immediately.

B The SNS topic queues the message but does not send it until manually triggered.

C The CloudWatch alarm automatically scales the EC2 instances without sending any notification.

D The alarm state change is logged but no notification is sent unless a Lambda function is attached.

💡 Hint

Think about how SNS works with subscriptions and notifications.

When a CloudWatch alarm triggers, it sends a message to the SNS topic, which immediately pushes the notification to all subscribed endpoints such as email, SMS, or Lambda.

❓ Architecture

intermediate

How does an Auto Scaling group respond to a CloudWatch alarm action?

An Auto Scaling group is configured with a CloudWatch alarm that triggers a scale-out policy when average CPU usage exceeds 70%. What is the expected result when the alarm triggers?

A The Auto Scaling group waits for manual approval before scaling out.

B The Auto Scaling group sends an SNS notification but does not change the number of instances.

C The Auto Scaling group launches additional instances according to the scaling policy immediately.

D The Auto Scaling group terminates instances to reduce CPU usage.

💡 Hint

Consider what a scale-out policy means for an Auto Scaling group.

When the alarm triggers a scale-out policy, the Auto Scaling group automatically launches more instances to handle increased load.

❓ security

advanced

Which IAM permission is required for CloudWatch to trigger Auto Scaling actions?

To allow CloudWatch alarms to trigger Auto Scaling policies, which IAM permission must be granted to the CloudWatch service or role?

A "cloudwatch:PutMetricAlarm" permission on the alarm resource.

B "ec2:TerminateInstances" permission on the EC2 instances.

C "sns:Publish" permission on the SNS topic resource.

D "autoscaling:ExecutePolicy" permission on the Auto Scaling group resource.

💡 Hint

Think about what action CloudWatch needs to perform to scale instances.

CloudWatch needs the "autoscaling:ExecutePolicy" permission to invoke scaling policies on the Auto Scaling group.

✅ Best Practice

advanced

What is a best practice when configuring SNS topics for CloudWatch alarm notifications?

When setting up SNS topics to receive CloudWatch alarm notifications, which practice improves security and reliability?

A Send notifications only to email endpoints without using encryption or access control.

B Use least privilege by restricting SNS topic access to only necessary subscribers and encrypt messages with AWS KMS.

C Allow open public access to the SNS topic so anyone can subscribe and receive notifications.

D Disable delivery retries to avoid duplicate notifications.

💡 Hint

Consider how to protect sensitive alarm notifications and control access.

Restricting access and encrypting messages ensures only authorized subscribers receive notifications securely.

🧠 Conceptual

expert

What is the sequence of events when a CloudWatch alarm triggers an Auto Scaling scale-in action and sends an SNS notification?

Order the following steps correctly when a CloudWatch alarm triggers a scale-in policy and sends a notification via SNS.

A 1,4,2,3

B 1,2,4,3

C 4,1,2,3

D 1,4,3,2

💡 Hint

Think about what happens first and how CloudWatch triggers multiple actions.

First, the alarm state changes. Then CloudWatch triggers both the scale-in policy and SNS notification. The SNS notification is sent while the Auto Scaling group terminates instances.

Practice

1. What is the primary purpose of connecting an AWS CloudWatch alarm to an SNS topic?

easy

A. To create backups of alarm configurations

B. To send notifications when the alarm state changes

C. To store alarm history logs

D. To automatically scale EC2 instances

Solution

1. Step 1: Understand SNS topic role

   SNS topics are used to send messages or notifications to subscribers.

2. Step 2: Connect alarm to SNS for notifications

   When an alarm changes state, it can trigger SNS to notify users or systems.

3. Final Answer:

   To send notifications when the alarm state changes -> Option B

4. Quick Check:

   Alarm + SNS = Notifications [OK]

Hint: SNS topics send messages on alarm changes [OK]

Common Mistakes:

• Confusing SNS with Auto Scaling actions
• Thinking SNS stores logs
• Assuming SNS creates backups

2. Which of the following is the correct way to specify an Auto Scaling action in a CloudWatch alarm configuration?

easy

A. {
"AlarmActions": ["arn:aws:autoscaling:region:account-id:scalingPolicy:policy-id:autoScalingGroupName/group-name:policyName/policy-name"]
}

B. AlarmActions: ["arn:aws:sns:region:account-id:topic-name"]

C. AlarmActions: ["arn:aws:lambda:region:account-id:function:function-name"]

D. AlarmActions: ["arn:aws:s3:::bucket-name"]

Solution

1. Step 1: Identify correct ARN format for Auto Scaling policy

   Auto Scaling policy ARNs include 'autoscaling' and specify scalingPolicy and group name.

2. Step 2: Match with given options

   { "AlarmActions": ["arn:aws:autoscaling:region:account-id:scalingPolicy:policy-id:autoScalingGroupName/group-name:policyName/policy-name"] } matches the correct ARN format for Auto Scaling alarm action.

3. Final Answer:

   Correct Auto Scaling policy ARN format -> Option A

4. Quick Check:

   Auto Scaling action uses autoscaling ARN [OK]

Hint: Auto Scaling ARNs contain 'autoscaling' keyword [OK]

Common Mistakes:

• Using SNS ARN instead of Auto Scaling ARN
• Confusing Lambda or S3 ARNs as alarm actions
• Incorrect ARN structure

3. Given this CloudWatch alarm configuration snippet:

{
  "AlarmName": "HighCPU",
  "MetricName": "CPUUtilization",
  "Namespace": "AWS/EC2",
  "Threshold": 80,
  "ComparisonOperator": "GreaterThanThreshold",
  "EvaluationPeriods": 2,
  "AlarmActions": ["arn:aws:sns:us-east-1:123456789012:NotifyMe"]
}

What happens when the CPU utilization exceeds 80% for 2 evaluation periods?

medium

A. An SNS notification is sent to subscribers of the NotifyMe topic

B. The EC2 instance automatically scales up

C. The alarm resets without any action

D. A Lambda function is triggered

Solution

1. Step 1: Analyze AlarmActions ARN

   The AlarmActions list contains an SNS topic ARN, meaning notifications are sent on alarm.

2. Step 2: Understand alarm trigger

   When CPUUtilization > 80% for 2 periods, alarm state changes and triggers SNS notification.

3. Final Answer:

   An SNS notification is sent to subscribers of the NotifyMe topic -> Option A

4. Quick Check:

   Alarm with SNS ARN sends notifications [OK]

Hint: SNS ARN in AlarmActions means notification sent [OK]

Common Mistakes:

• Assuming Auto Scaling happens without scaling policy
• Thinking alarm resets silently
• Confusing SNS with Lambda triggers

4. You configured a CloudWatch alarm to trigger an Auto Scaling policy, but the instances are not scaling when the alarm state changes. What is the most likely cause?

medium

A. The EC2 instances are stopped

B. The SNS topic subscription is missing

C. The alarm threshold is set too low

D. The alarm's AlarmActions does not include the correct Auto Scaling policy ARN

Solution

1. Step 1: Check AlarmActions configuration

   If the Auto Scaling policy ARN is missing or incorrect, the alarm cannot trigger scaling.

2. Step 2: Rule out other options

   SNS subscription missing affects notifications, not scaling. Threshold too low triggers alarm but no scaling if policy missing. Stopped instances do not scale but alarm triggers still need correct action.

3. Final Answer:

   The alarm's AlarmActions does not include the correct Auto Scaling policy ARN -> Option D

4. Quick Check:

   Correct Auto Scaling ARN needed in AlarmActions [OK]

Hint: Auto Scaling needs correct policy ARN in AlarmActions [OK]

Common Mistakes:

• Confusing SNS subscription with scaling trigger
• Ignoring ARN correctness
• Assuming stopped instances auto scale

5. You want to automatically increase the number of EC2 instances when CPU usage is high and send a notification to your team. Which combination of alarm actions should you configure?

hard

A. Add only the Auto Scaling policy ARN to AlarmActions

B. Add only the SNS topic ARN to AlarmActions

C. Add both the Auto Scaling policy ARN and the SNS topic ARN to the alarm's AlarmActions

D. Create two separate alarms, one for scaling and one for notifications

Solution

1. Step 1: Understand alarm actions for scaling and notifications

   To scale automatically, the alarm must trigger the Auto Scaling policy. To notify, it must trigger the SNS topic.

2. Step 2: Combine both actions in one alarm

   Adding both ARNs in AlarmActions ensures the alarm triggers scaling and sends notifications simultaneously.

3. Final Answer:

   Add both the Auto Scaling policy ARN and the SNS topic ARN to the alarm's AlarmActions -> Option C

4. Quick Check:

   Multiple AlarmActions allow scaling + notifications [OK]

Hint: Use both Auto Scaling and SNS ARNs in AlarmActions [OK]

Common Mistakes:

• Thinking one ARN can do both scaling and notifications
• Creating multiple alarms unnecessarily
• Missing one of the required ARNs