How to enable auto notifications when backend server is down.

There are a few ways you can set up email notifications when your backend server goes down:

1. Use Amazon CloudWatch and Simple Notification Service (SNS):

   • Create an SNS topic for notifications
   • Set up a CloudWatch alarm to monitor your backend server's status
   • Configure the alarm to send notifications to the SNS topic when the server is down
   • Subscribe your email address to the SNS topic to receive notifications

2. Implement a health check system:

   • Create a simple health check endpoint on your backend server
   • Set up a monitoring service or script to periodically ping this endpoint
   • If the health check fails, trigger an email notification

3. Use AWS EventBridge:

   • Create a rule in EventBridge to detect state changes in your backend server
   • Configure the rule to send notifications to an SNS topic when the server status changes to "terminated" or "stopped"
   • Subscribe your email to the SNS topic

4. Implement error handling in your application:

   • Add error handling code in your application to detect when the server is unresponsive
   • Use Amazon Simple Email Service (SES) or another email service to send notifications when errors are detected

These methods can be customized to fit your specific needs and infrastructure. Remember to test your notification system to ensure it works as expected.
Sources
how to configure Amazon simple Email service | AWS re:Post
EC2 user data script failure alert | AWS re:Post

Hello.

In addition to re:Post Agent's answer, I think it would be a good idea to use CloudWatch Synthetics to set up external monitoring if the application has a backend server listening on HTTPS etc.
https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Canaries.html