<span dir="LTR">You have deployed a Java application in an AWS Auto Scaling group. The application has sent its logs to an AWS CloudWatch Log Group. You want to deliver the log events from the CloudWatch Log Group to a Lambda function in real-time for custom processing and analysis. As the Lambda function is designed to process only the logs that contain certain keywords, you need a filter pattern that defines which log events should be forwarded. How would you implement this?</span>

Answer options:

A.In the CloudWatch Log Group, create a metric filter to send the log data to the AWS Lambda function. Set up a filter pattern in the metric filter to specify which logs are forwarded.
B.In the CloudWatch Log Group, create a subscription filter that sends the log data to the AWS Lambda function. Set up the filter pattern in the subscription filter to specify which logs are forwarded.
C.Select the log stream of the CloudWatch Log Group and click “Export results”. Choose the Lambda function and configure the filter pattern.
D.Select the CloudWatch Log Group and click “Export data to Lambda”. Choose your Lambda function and define the filter pattern.

Correct Answer : B
Option A is incorrect because a metric filter is used to search and filter the log data and turn log data into CloudWatch metrics. However, it cannot forward log events to a Lambda function in real time.
Option B is CORRECT because a subscription filter can forward logs to services such as an Amazon Kinesis stream, an Amazon Kinesis Data Firehose stream, or AWS Lambda in real-time. You can also define a filter pattern in the subscription filter. Please check the following references for details.
Option C is incorrect because the “Export results” feature of CloudWatch Log Stream is used to download the log events. It cannot forward logs to a Lambda function in real-time.
Option D is incorrect because in CloudWatch Log Group, you cannot directly export the log data to a Lambda function. You would need to create a subscription filter for this task.
Reference:
https://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/Subscriptions.html 
https://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/SubscriptionFilters.html#LambdaFunctionExample