Question 512 of 247
How to Count Errors in CloudWatch Logs and Alert with Metric Filters
A SysOps team needs to monitor application logs in Amazon CloudWatch Logs for specific error codes and automatically invoke an AWS Lambda function for remediation within 5 minutes of an error occurring. Which solution involves the least operational overhead?
Quick Answer
The correct answer is to create a CloudWatch metric filter on the log group, a CloudWatch alarm on that metric, and configure the alarm to post to an SNS topic that triggers the Lambda function. This solution works because the metric filter continuously scans incoming log events for the specified error pattern, incrementing a custom metric each time it matches, and the alarm evaluates that metric against a threshold—all within a fully managed, serverless pipeline that requires no custom polling code or infrastructure to maintain. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of how to count error occurrences in CloudWatch Logs with metric filter and alarm, and the common trap is overcomplicating the solution by suggesting a custom script or a separate EC2 instance to parse logs, which adds unnecessary operational overhead. Remember that CloudWatch is designed to be the single pane of glass for monitoring—if you need to react to log patterns, always start with a metric filter. Memory tip: “Filter, Alarm, Trigger”—think of the metric filter as the lookout, the alarm as the decision-maker, and SNS as the messenger to Lambda.
⚠ Common exam trap
It's easy for candidates to assume a subscription filter (Option A) is the simplest because it directly streams logs to Lambda, but they overlook that it lacks native filtering for specific error codes and requires the Lambda to process all log events, increasing complexity and cost compared to a metric filter and alarm.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a CloudWatch metric filter on the log group, create a CloudWatch alarm on the metric, and configure the alarm to post to an SNS topic that triggers the Lambda function.
It uses CloudWatch metric filters and alarms to detect error codes in logs and trigger remediation via SNS and Lambda, all within a fully managed AWS pipeline. This approach requires no custom code or infrastructure to maintain, and the alarm can be configured to evaluate logs within a 1-minute period, easily meeting the 5-minute requirement with minimal operational overhead.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create a CloudWatch Logs subscription filter to stream logs directly to an AWS Lambda function.
Why it's wrong here
Incorrect. While possible, this processes every log event, increasing cost and complexity. It does not natively aggregate errors for alarm triggering.
- ✓
Create a CloudWatch metric filter on the log group, create a CloudWatch alarm on the metric, and configure the alarm to post to an SNS topic that triggers the Lambda function.
Why this is correct
Correct. This uses native CloudWatch features with minimal overhead, meeting the 5-minute requirement through alarm evaluation intervals.
- ✗
Use a third-party log aggregation tool that sends webhook notifications to an API Gateway endpoint to invoke the Lambda function.
Why it's wrong here
Incorrect. This introduces external dependencies and additional operational overhead to manage the third-party tool.
- ✗
Write a custom script that runs on an EC2 instance to poll CloudWatch Logs every minute and invoke the Lambda function.
Why it's wrong here
Incorrect. This requires managing an EC2 instance and custom scripting, adding significant overhead.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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Same concept, more angles
3 more ways this is tested on SOA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company uses Amazon CloudWatch Logs to store application logs. The SysOps administrator needs to count the occurrences of the string 'ERROR' in the logs and trigger an Amazon SNS notification when more than 10 errors occur within a 5-minute window. Which steps should the administrator take?
easy- ✓ A.Create a metric filter on the log group and then create a CloudWatch alarm on the resulting metric
- B.Create a CloudWatch alarm directly on the log group
- C.Create an AWS Lambda function to parse the logs and send a notification to Amazon SNS
- D.Create an Amazon EventBridge rule to filter log events and send to SNS
Why A: A metric filter on a CloudWatch Logs log group extracts a numeric metric (e.g., count of 'ERROR' occurrences) and publishes it to a CloudWatch custom metric. A CloudWatch alarm can then be configured on that metric to evaluate a threshold (e.g., >10) over a specified period (e.g., 5 minutes) and trigger an SNS notification when breached. This is the native, serverless, and cost-effective approach for counting log patterns and alerting.
Variation 2. A company uses Amazon CloudWatch Logs to store application logs. The SysOps administrator needs to detect when the number of log entries containing the string 'ERROR' exceeds 100 in any 5-minute window. When this threshold is breached, an email should be sent to the operations team. Which combination of AWS services should be used with the least operational overhead?
easy- A.CloudWatch Logs Insights scheduled query with SNS action.
- ✓ B.Create a metric filter on the log group for 'ERROR', then create a CloudWatch alarm on that metric with an SNS action to send email.
- C.Use a Lambda function that reads the log stream and sends an email via Amazon Simple Email Service (SES) when errors exceed 100.
- D.Install an agent on the application server that sends logs to Amazon SQS, then poll the queue with a Lambda function to trigger an email.
Why B: It uses CloudWatch metric filters to extract the count of 'ERROR' log entries as a custom metric, then a CloudWatch alarm on that metric triggers an SNS topic to send email notifications. This approach requires no custom code or additional infrastructure, minimizing operational overhead while meeting the requirement of detecting >100 errors in any 5-minute period.
Variation 3. An application writes error logs to Amazon CloudWatch Logs. The SysOps administrator needs to monitor for the occurrence of the string 'ERROR' in the logs and trigger an Amazon SNS notification if more than 10 errors occur within a 5-minute window. The administrator also wants to visualize the error count over time. Which approach should be used to meet these requirements with the least operational overhead?
medium- ✓ A.Create a CloudWatch Logs metric filter to count 'ERROR' entries, then create a CloudWatch alarm on that metric with a period of 5 minutes and a threshold of 10.
- B.Use CloudWatch Logs Insights to run a query every 5 minutes and send notifications via a scheduled AWS Lambda function.
- C.Create an AWS Lambda function that processes log events in real-time and publishes to Amazon SNS when the error count exceeds 10 in 5 minutes.
- D.Use Amazon EventBridge to match log events with the pattern 'ERROR' and send them to an SNS topic.
Why A: CloudWatch Logs metric filters can extract a count of 'ERROR' occurrences from incoming log events and emit a custom metric. A CloudWatch alarm on that metric with a period of 5 minutes and a threshold of 10 directly triggers an SNS notification when the error count exceeds 10 within the window, and the metric itself can be graphed in CloudWatch dashboards for visualization—all with minimal configuration and no custom code.
Last reviewed: Jun 11, 2026
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