Correct answer - "CloudWatch Event Rules with AWS Lambda" : You can create a Lambda function and
direct AWS Lambda to execute it on a regular schedule. You can specify a fixed rate (for
example, execute a Lambda function every hour or 15 minutes), or you can specify a Cron
expression.
"AWS Lambda Custom Sources" - There is no custom source option
"Open a support ticket with AWS" - You can although they will not add a custom source they will
step you through creating event rule with Lambda
"Cron jobs to trigger AWS Lambda to check the state of your service" - You would need an
additional server for your cron job instead use a cron expression with CloudWatch