CloudWatch, Alarms & X-Ray

CloudWatch, Alarms & X-Ray

Step 1 of 11

Every incident asks three things in order: is it broken, where, and why. Each has its own tool.

The Idea

CloudWatch metrics are numbers per period, named by namespace and dimensions. An alarm compares a metric with a threshold over several periods and moves between OK, ALARM and INSUFFICIENT_DATA; its actions can notify SNS or scale a group. CloudWatch Logs holds log groups you query with Logs Insights. X-Ray follows one request across services as a trace of segments.

Real-World Example

After a bad deploy, the load balancer's 5XX count breaches for three periods and the alarm pages on-call through SNS. A trace shows the time disappearing into a database call; a Logs Insights query finds "pool exhausted".

The Tradeoff

Alarm on symptoms users feel — errors, latency — or pages become noise. X-Ray's SDKs and daemon entered maintenance mode in February 2026; AWS recommends OpenTelemetry for new instrumentation. CloudTrail, not CloudWatch, records who called which API.

Hands-On

# illustrative — load balancer name and topic ARN are placeholders
aws cloudwatch put-metric-alarm --alarm-name api-5xx \
  --namespace AWS/ApplicationELB --metric-name HTTPCode_Target_5XX_Count \
  --dimensions Name=LoadBalancer,Value=app/web/1234567890abcdef \
  --statistic Sum --period 60 --evaluation-periods 3 --threshold 10 \
  --comparison-operator GreaterThanOrEqualToThreshold \
  --alarm-actions arn:aws:sns:us-east-1:123456789012:oncall

Your turn

Put the steps in the right order.

1. 1A trace shows which service the time went to↑↓
2. 2The alarm moves to ALARM and notifies SNS↑↓
3. 3The 5XX metric breaches its threshold for several periods↑↓
4. 4A log query finds the error behind it↑↓

Check order

Mini quiz

1 / 3

An alarm with 3 evaluation periods moves to ALARM when:

• AThe metric breaches once
• BEnough of the recent periods breach — for example 3 out of 3
• CAny log line contains ERROR
• DA trace is slower than average

Sources

• Alarm evaluation — Amazon CloudWatch User Guide
• Amazon CloudWatch Logs concepts — CloudWatch Logs User Guide
• AWS X-Ray concepts — AWS X-Ray Developer Guide
• X-Ray SDK and daemon support timeline — AWS X-Ray Developer Guide