Understanding AWS CloudWatch Alarms: Listen to Your Cloud Signals

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 / OR logic.
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.