CloudWatch is AWS’s monitoring hub. It collects:

• Metrics — numeric time-series (EC2 CPU, Lambda invocations); custom metrics too
• Logs — application/system logs sent to log groups, queried with Logs Insights
• Alarms — fire when a metric breaches a threshold, triggering SNS, Auto Scaling, or automation
• Events / EventBridge — react to state changes (rules → targets)

Related: CloudTrail records API activity (who did what — auditing), while X-Ray traces requests across services. Don’t confuse CloudWatch (metrics/logs) with CloudTrail (audit log).

# Alarm: notify when EC2 CPU > 80% for 5 minutes
aws cloudwatch put-metric-alarm \
  --alarm-name high-cpu --namespace AWS/EC2 \
  --metric-name CPUUtilization --statistic Average \
  --period 300 --threshold 80 --comparison-operator GreaterThanThreshold \
  --evaluation-periods 1 --alarm-actions arn:aws:sns:...:ops-alerts

Logs Insights query:
  fields @timestamp, @message
  | filter @message like /ERROR/
  | sort @timestamp desc | limit 20

1. Define an alarm (in words) for a Lambda error-rate spike.
2. Explain the difference between CloudWatch and CloudTrail.
3. Write a Logs Insights query idea to count errors per hour.
4. Describe how an alarm can trigger Auto Scaling.

• ↗ AWS — CloudWatch