Amazon EC2 Instance from Custom AMI Health Check Failing

The issue you're experiencing with your custom AMI and failing health checks is likely related to the instance initialization process. When an EC2 instance is launched, it undergoes two primary status checks:

1. System Status Check: This checks the AWS infrastructure that the instance runs on.
2. Instance Status Check: This monitors the software and network configuration of your instance.

If both checks are failing (0/2 Status Checks), it suggests there might be problems with the instance's operating system, networking, or software configuration. Here are some potential causes and solutions:

1. Cloud-init issues: Your custom AMI might have problems with cloud-init, which is responsible for instance initialization. Check the system logs for any cloud-init errors.

2. Network configuration: Ensure that the network settings in your custom AMI are correctly configured for the new instance.

3. Operating system issues: There might be problems with the OS itself, preventing proper boot-up or initialization.

4. Resource constraints: Check if the instance has sufficient CPU, memory, or disk space to start properly.

5. Software conflicts: Custom software or configurations in your AMI might be causing conflicts during instance startup.

To troubleshoot:

1. Review the instance's system logs through the EC2 console to identify specific errors.

2. Try launching the instance in a different availability zone or with a different instance type to rule out infrastructure issues.

3. If possible, use Amazon EC2 Rescue for Linux to diagnose and fix common issues that prevent remote access.

4. Consider using the AWSSupport-TroubleshootSSH automation runbook if you have Systems Manager configured. This tool can help identify and fix common SSH connection issues.

5. If the problem persists, you may need to revisit your AMI creation process and ensure all configurations are compatible with the EC2 environment.

Remember, for spot instances, it's crucial to have a quickly initializing and stable AMI, as spot instances can be terminated with short notice. Ensure your custom AMI is optimized for fast boot times and stable operation in a spot environment.
Sources
My AMI not working as expected | AWS re:Post
EC2 instance launching error | AWS re:Post
1/3 checks passed for Ec2 | AWS re:Post
Can't connect to Linux instance even after the health status checks pass | AWS re:Post