An online retailer runs its checkout API behind an Application Load Balancer. The team has a metric for successful checkout responses and a metric for failed responses, both published once per minute.
The on-call team wants a page when the checkout error rate exceeds 2 percent for five minutes, and a separate, quieter notification when latency is high but the error rate is normal. The page must not fire on a single bad minute, and the team does not want to maintain any Lambda functions for the alarms.
Which TWO actions meet these requirements? (Choose two.)
Choose two answers.
AA. Create one alarm on the p99 latency statistic of the load balancer's response time, and send it to the same paging topic as the error alarm so that each slow request pages on-call.
BB. Create one alarm for each target instance on its own failed-response count, and page on-call when any instance's alarm turns into ALARM state.
CC. Create an alarm that uses metric math to divide the failed-response count by the sum of both counts, times 100, and alarm when that expression stays above 2 for five consecutive one-minute periods.
DD. Create a Logs Insights query that computes the error rate every minute and a scheduled rule that starts an SNS notification whenever the query returns a result over 2 percent.
EE. Create a composite alarm with the rule ALARM(latency) AND NOT ALARM(error-rate), and route it to the quieter channel, while the error-rate alarm itself notifies the paging topic.
Show the answer and explanation
Answers: C, E
A. Wrong: A single slow request should not page on-call, and the latency alarm would page on every slow period. Sending it to the paging topic also removes the quieter notification the team asked for. Learn more: Using Amazon CloudWatch alarms (opens in a new tab)
C. Right: Correct. A metric math expression can compute the error percentage from the two metrics, and the datapoints-to-alarm setting requires five breaching minutes. The alarm therefore ignores a single bad minute. Learn more: Math expressions with metrics (opens in a new tab)
E. Right: Correct. The composite alarm goes into ALARM only when latency is high and the error-rate alarm is not firing, so it drives the quieter notification. The error-rate alarm pages on its own, so a real checkout failure always pages. Learn more: Composite alarms (opens in a new tab)
Explanation
A metric math alarm can compute the error percentage from the two metrics and require several consecutive breaching periods, so one bad minute does not page. A composite alarm with the rule ALARM(latency) AND NOT ALARM(error-rate) sends the quieter notification only when latency is the sole problem. Per-instance alarms, latency-only paging and scheduled Logs Insights queries each miss a requirement.
Want more on Custom metrics, metric filters and alarms? The 5 full-length practice sets have 14 more Custom metrics, metric filters and alarms questions, 375 in all, none of them in the free exam. One payment of $14.99, no subscription. See the practice sets →