An application runs on Amazon EC2 instances that are in an Auto Scaling group.

Deploy and configure the Amazon CloudWatch agent on the EC2 instances to log to a CloudWatch Log group. Create a metric filter on the target CloudWatch Log group. Create a CloudWatch alarm that publishes to an Amazon Simple Notification Service (Amazon SNS) topic that has an email subscription.

Create a cron job on the EC2 instances to identify errors and push the errors to an Amazon CloudWatch metric filter. Configure the filter to publish to an Amazon Simple Notification Service (Amazon SNS) topic that has an SMS subscription.

Deploy an AWS Lambda function that pushes the errors directly to Amazon CloudWatch Logs. Configure the Lambda function to run every time the log file is updated on disk.

Create an Auto Scaling lifecycle hook that invokes an EC2 based script to identify errors. Configure the script to push the error messages to an Amazon CloudWatch log group when the EC2 instances scale in. Create a CloudWatch alarm that publishes to an Amazon Simple Notification Service (Amazon SNS) topic that has an email subscription when the number of error messages exceeds a threshold.