Understanding AWS CloudWatch Alarms: Listen to Your Cloud Signals
CloudWatch Alarms monitor metrics and take action when thresholds are crossed.
Hello! I'm Jay Tillu, an Information Security Engineer at Simple2Call. I have expertise in security frameworks and compliance, including NIST, ISO 27001, and ISO 27701. My specialities include Vulnerability Management, Threat Analysis, and Incident Response. I have also earned certifications in Google Cybersecurity and Microsoft Azure. I’m always eager to connect and discuss cybersecurity—let's get in touch!
Arjun once asked himself a question that every AWS beginner stumbles upon:
“Okay, CloudWatch collects metrics… but how do I do something when something goes wrong?”
That’s where CloudWatch Alarms enter the chat — the silent watchdogs of your AWS infrastructure.
🎯 What Are CloudWatch Alarms?
CloudWatch Alarms monitor metrics and take action when thresholds are crossed.
Think of it like this:
“If CPU usage is over 80% for 5 minutes, alert me!”
“If disk space drops below 10%, reboot the instance!”
Simple rules, powerful outcomes.
🚦 Alarms Have 3 States
| State | Meaning |
✅ OK | All is well. |
⏳ INSUFFICIENT_DATA | Not enough data to decide. |
🔴 ALARM | Threshold crossed. Take action! |
⏱️ The Heartbeat: Period
Period = how often you check the metric.
Can be as short as 10 seconds (high-resolution metric)
Or as long as 5 minutes, depending on what you need
Arjun set his alarm to check CPU every 60 seconds. That was enough for his use case.
🛠️ What Can an Alarm Do?
An alarm isn’t just about shouting.
It can actually do things:
Take action on EC2 instances
- Stop, terminate, reboot, recover
Trigger Auto Scaling
- Add/remove EC2s based on load
Send notifications
🔔 Push to SNS topic
📩 Notify email/SMS
🤖 Call Lambda for custom logic
When Arjun’s app went down once due to a full disk, he set up an alarm that automatically notified him AND triggered a Lambda to clean up logs. Crisis avoided.
🤹♂️ Composite Alarms — The Smart Combo
Arjun noticed a problem: too many alarms were firing. He needed to get smart.
So he used Composite Alarms.
Here’s how they work:
Combine multiple alarms using
AND/ORlogic.Get notified only when multiple conditions are true.
Example:
✅ CPU > 80% AND Disk I/O high → Trigger alert
❌ CPU > 80% but Disk I/O normal → Ignore it
This helped Arjun reduce alarm noise and focus only on real issues.
🛡️ EC2 Instance Recovery with Alarms
Arjun wanted peace of mind in case EC2 failed. So he used CloudWatch Alarms to trigger EC2 recovery based on status checks:
| Check Type | What It Monitors |
| Instance Status | EC2 OS health (like kernel panic) |
| System Status | Host hardware issues |
| EBS Status | Attached disk health |
If the host failed, the alarm automatically moved his instance to a healthy host.
Same IP. Same data. No stress.
🧠 Bonus: Log-Based Alarms
Arjun was monitoring an app log file for the word ERROR. He created a CloudWatch Log Metric Filter, and tied that to an alarm.
Now if ERROR appears more than 10 times in 5 minutes, he gets an alert.
Simple setup. High confidence.
🧪 Test Before You Trust
Before going live, Arjun tested everything using this CLI command:
aws cloudwatch set-alarm-state \
--alarm-name "CPUHigh" \
--state-value ALARM \
--state-reason "Testing alarm action"
This simulated a breach and confirmed SNS and Lambda triggers were working.
📌 SAA-Certified Knowledge
If you're prepping for the AWS SAA exam, remember:
✅ CloudWatch Alarms monitor metrics
✅ Can trigger EC2 actions, SNS, Auto Scaling
✅ Composite Alarms = Combine logic across alarms
✅ Can be tied to Log Metric Filters
✅ Support EC2 recovery actions
✅ Use IAM roles properly when needed
✅ CLI command: set-alarm-state for testing
🧘 Arjun’s Takeaway
“CloudWatch collects data.
Alarms give it a voice.”
He now sleeps peacefully, knowing CloudWatch is watching over his infrastructure — and will shout (or act) if anything goes wrong.
Read More on AWS Monitoring
Understanding AWS EventBridge: The Automation Service Explained
Understanding AWS CloudWatch Alarms: Listen to Your Cloud Signals
How CloudWatch Agent Completes EC2 Monitoring: A Comprehensive Guide
