You’ve just deployed an AWS Lambda function. This Lambda function would be invoked via the API gateway service. You want to know if there were any errors while the Lambda function was being invoked. Which of the following service would allow you to check the performance of your underlying Lambda function?

Answer options:

A.VPC Flow Logs
B.Cloudwatch
C.Cloudtrail
D.AWS Trusted Advisor

Answer – B
In AWS Lambda, you can use Cloudwatch metrics to see the number of Invocation errors. The below snapshot from the AWS Documentation shows an example of this.
Accessing Amazon CloudWatch Metrics for AWS Lambda
AWS Lambda automatically monitors functions on your behalf, reporting metrics through Amazon CloudWatch. These metrics include total requests, latency, and error rates. For more information about Lambda metrics, see AWS Lambda Metrics. For more information about CloudWatch, see the Amazon CloudWatch User Guide.
You can monitor metrics for Lambda and view logs by using the Lambda console, the CloudWatch console, the AWS CLI, or the CloudWatch API. The following procedures show you how to access metrics using these different methods.
To access metrics using the Lambda console
Sign in to the AWS Management Console and open the AWS Lambda console at https://console.aws.amazon.com/lambda/.
On the Functions page, choose the function name and then choose the Monitoring tab.
Option A is invalid because this service is used to get the network traffic entering your VPC.Option C is invalid because this service is used to monitor API Activity.
Option D is invalid because this service does not have the ability to give you the metrics for the Lambda service.
For more information on accessing metrics for AWS Lambda, please refer to the below link-
https://docs.aws.amazon.com/lambda/latest/dg/monitoring-functions-access-metrics.html