Log Insight

Observing via Log Insight

Objectives

• Monitor queries and performance of the entire request flow.
• Log in a standardized structured format (JSON).
• Efficiently query logs using CloudWatch Logs Insights to optimize performance.
• Analyze slow queries, 4xx/5xx errors, DynamoDB throttling, and cost impacts.

Steps

1. Go to CloudWatch Console

• Navigate to CloudWatch → Logs Insights
• Select a log group: /aws/lambda/my-function or /aws/apigateway/...

2. Sample Logs Insights Queries for Lambda

• Query Lambda errors (status code 4xx, 5xx):

fields @timestamp, @message
| filter @message like /ERROR/
| sort @timestamp desc
| limit 100

Sample log analysis content:

• Error type: [ERROR] ClientError: An error occurred (AccessDenied) when calling the PutMetricData operation.
• Description: The Lambda function is trying to call CloudWatch’s PutMetricData API to push metrics but was denied access (AccessDenied).
• Cause: The user or role assigned to the Lambda function lacks permission to call PutMetricData.
• Location: Lambda function named create_user in the ap-southeast-1 region.
• Other log info includes: timestamp, account ID, environment, log stream, and traceback from the Python Lambda code.

Statistics on Lambda runtime and resource usage (duration, memory):

	filter @type = "REPORT"
	| stats avg(@duration) as AverageDuration,
        max(@duration) as MaxDuration,
        min(@duration) as MinDuration,
        avg(@maxMemoryUsed/1024/1024) as AverageMemoryUsedMB,
        max(@maxMemoryUsed/1024/1024) as MaxMemoryUsedMB,
        min(@maxMemoryUsed/1024/1024) as MinMemoryUsedMB

Explanation:

• AverageDurationMS: Average execution time of the Lambda function within the queried time range (in milliseconds).

• MaxDuration: Maximum execution time during that period.

• MinDuration: Minimum execution time.

• AverageMemoryUsedMB: Average memory used (MB).

• MaxMemoryUsedMB: Maximum memory used.

• MinMemoryUsedMB: Minimum memory used.

• Analyze Lambda latency (duration) over time:

	filter @type = "REPORT"
	| stats avg(@duration), max(@duration), min(@duration) by bin(5m)

3. Generate queries using the prompt

• Enter your desired query in the Prompt field.

• Click Generate new query to create the query, then click Run query to execute it.

	Cold start rate as a percentage of total Lambda invocations