Comprehensive Guide to Migrating EC2 Instance Store-Backed Instances

Introduction

As AWS environments evolve, the need to migrate EC2 instances to different instance types is a common operational task. While migrating EBS-backed instances is relatively straightforward, migrating instance store-backed instances presents unique challenges due to their ephemeral storage characteristics. This guide provides a detailed walkthrough of the migration process for instance store-backed instances, covering essential considerations, step-by-step procedures, and best practices that will help you prepare for the AWS SysOps Administrator certification exam.

Understanding Instance Store-Backed Instances

Before diving into the migration process, it’s crucial to understand the fundamental characteristics of instance store-backed instances:

• Instance store-backed instances use physical storage that is directly attached to the host computer
• The data on instance store volumes is ephemeral – it persists only during the lifetime of the instance
• If the instance stops, terminates, or the underlying hardware fails, all data on the instance store is lost
• These instances cannot be stopped and restarted like EBS-backed instances
• Changing the instance type directly (as you would with an EBS-backed instance) is not possible

Because of these characteristics, migrating instance store-backed instances requires a more complex approach than simply using the “Change Instance Type” feature.

Migration Options Overview

There are two primary approaches for migrating instance store-backed instances:

1. Creating and using an AMI: Create an AMI from the running instance, then launch a new instance of the desired type from that AMI
2. Manual data transfer: Set up and transfer data manually between the old and new instances

The AMI approach is generally more efficient and is the focus of this guide.

Detailed Migration Process Using AMI

Phase 1: Preparation and Planning

Step 1: Assessment and Planning

Before starting the migration, complete these critical planning steps:

• Identify target instance type: Determine the appropriate instance type based on your workload requirements (compute, memory, storage, network performance)
• Check compatibility: Verify that your application and operating system are compatible with the target instance type
• Review network configurations: Document all security groups, elastic IPs, IAM roles, and network interfaces
• Plan for downtime: Schedule the migration during a maintenance window as the process will involve instance restart
• Create a backup: Although you’ll create an AMI, having additional backups is a best practice

Step 2: Check AMI Creation Requirements

Ensure you have:

• AWS CLI installed and configured with appropriate permissions
• Required IAM permissions to create AMIs, launch instances, and create/attach volumes
• Sufficient S3 storage for the AMI (the bundling process stores the AMI in S3)
• The EC2 AMI tools installed on the instance (if it’s an older instance)

Phase 2: Creating an AMI from the Instance Store-Backed Instance

Step 1: Install Required Tools (if not already installed)

For Amazon Linux:

sudo yum install -y ec2-ami-tools

For Ubuntu:

sudo apt-get update
sudo apt-get install -y ec2-ami-tools

Step 2: Prepare Your Instance

Remove sensitive data and unnecessary files to reduce AMI size and improve security:

sudo rm -rf /tmp/*
sudo rm -f /var/log/*.gz
history -c

Step 3: Upload X.509 Certificate and Private Key to the Instance

You’ll need the certificate and private key for the bundling process:

scp -i your-key.pem /path/to/cert-xxxxx.pem ec2-user@your-instance-ip:~/
scp -i your-key.pem /path/to/pk-xxxxx.pem ec2-user@your-instance-ip:~/

Step 4: Create a Temporary Directory for the Bundle

mkdir ~/ami-bundle

Step 5: Bundle the Instance Volume

For Amazon Linux/RHEL/CentOS:

sudo ec2-bundle-vol \
    -k ~/pk-xxxxx.pem \
    -c ~/cert-xxxxx.pem \
    -u your-aws-account-id-without-hyphens \
    -d ~/ami-bundle \
    -r x86_64 \
    -p image-name \
    --partition mbr

For Ubuntu:

sudo ec2-bundle-vol \
    -k ~/pk-xxxxx.pem \
    -c ~/cert-xxxxx.pem \
    -u your-aws-account-id-without-hyphens \
    -d ~/ami-bundle \
    -r x86_64 \
    -p image-name \
    --partition mbr \
    --no-filter

Step 6: Upload the Bundle to Amazon S3

ec2-upload-bundle \
    --bucket your-s3-bucket \
    --manifest ~/ami-bundle/image-name.manifest.xml \
    --access-key your-access-key \
    --secret-key your-secret-key \
    --region your-region

Step 7: Register the AMI

Using the AWS CLI:

aws ec2 register-image \
    --name "My Instance Store AMI" \
    --description "AMI created from instance store-backed instance" \
    --image-location your-s3-bucket/image-name.manifest.xml \
    --virtualization-type hvm \
    --architecture x86_64 \
    --root-device-name /dev/sda1

Phase 3: Launching a New Instance from the AMI

Step 1: Launch a New Instance of the Desired Type

Using the AWS CLI:

aws ec2 run-instances \
    --image-id ami-12345678 \
    --instance-type new-instance-type \
    --key-name your-key-pair \
    --security-group-ids sg-12345678 \
    --subnet-id subnet-12345678

Or through the AWS Management Console:

1. Navigate to EC2 Dashboard
2. Click “Launch Instance”
3. Select “My AMIs” and choose the AMI you created
4. Select the desired instance type
5. Configure instance details (subnet, IAM role, etc.)
6. Add storage as needed
7. Configure security groups
8. Launch the instance

Step 2: Configure the New Instance

After the new instance is running:

1. If you had an Elastic IP attached to the original instance, reassociate it with the new instance
2. Update any DNS records pointing to the instance
3. Verify that all required applications start correctly
4. Test the functionality of the applications

Step 3: Validation and Testing

Perform thorough testing to ensure:

• All applications are functioning correctly
• Performance meets expectations on the new instance type
• All data has been properly migrated
• Network connectivity and security settings are working correctly

Phase 4: Clean-up and Documentation

Step 1: Clean-up Resources

Once you’ve confirmed the new instance is working properly:

1. Deregister the AMI if you no longer need it:

aws ec2 deregister-image --image-id ami-12345678

2. Delete the bundle from S3:

aws s3 rm s3://your-s3-bucket/image-name.manifest.xml
aws s3 rm --recursive s3://your-s3-bucket/image-name/

3. Terminate the old instance (only after confirming the new instance is fully operational):

aws ec2 terminate-instances --instance-ids i-12345678

Step 2: Documentation

Document the migration process including:

• Original and new instance specifications
• Any configuration changes made during migration
• Issues encountered and how they were resolved
• Performance comparisons between old and new instances

Alternative Approach: Manual Data Transfer

If creating an AMI isn’t feasible or you prefer a more controlled approach, you can manually transfer data:

1. Launch a new instance of the desired type (EBS-backed for future flexibility)
2. Install and configure applications on the new instance
3. Transfer data using methods like:
   • rsync or scp for direct file transfer
   • AWS S3 as an intermediary storage
   • Database dumps and restores for database content
4. Update configuration files on the new instance
5. Test thoroughly before switching over
6. Update DNS/Elastic IP to point to the new instance

Example rsync command for data transfer:

rsync -avz -e "ssh -i key.pem" /source/directory/ ec2-user@new-instance-ip:/destination/directory/

Special Considerations for Production Environments

When migrating production instances, additional considerations are necessary:

Minimizing Downtime

To minimize service disruption:

• Use load balancers to gradually shift traffic to the new instance
• Implement a blue-green deployment approach
• Synchronize data continuously until the cutover
• Schedule the final migration during low-traffic periods

Handling Stateful Applications

For applications that maintain state:

• Implement proper application shutdown procedures to ensure data consistency
• For databases, consider using replication to sync data before the final cutover
• Test state persistence after migration

Performance Considerations

• Run performance benchmarks on both old and new instances
• Monitor performance metrics closely after migration
• Be prepared to adjust instance size if performance doesn’t meet expectations

AWS Exam Focus Areas

For the AWS SysOps Administrator exam, be prepared to answer questions about:

1. Differences between instance store-backed and EBS-backed instances
   • Persistence characteristics
   • Startup/shutdown behavior
   • Modification capabilities
2. AMI creation process
   • Tools and permissions required
   • Regional considerations
   • Sharing and security
3. Migration strategies
   • When to use each approach
   • Steps to minimize downtime
   • Validation requirements
4. Troubleshooting migration issues
   • Common errors during AMI creation
   • Network configuration problems
   • Permission-related issues

Common Challenges and Solutions

Challenge 1: Large Data Volumes

Problem: Bundling large volumes can take a long time and might fail.

Solution:

• Clean up unnecessary files before bundling
• Consider splitting the migration (application files vs. data)
• Use incremental backup tools to reduce transfer time

Challenge 2: Specialized Instance Types

Problem: Some workloads require specialized instance types (GPU, high I/O, etc.).

Solution:

• Verify compatibility of specialized drivers with the new instance type
• Test application performance on smaller instances before full migration
• Consider containerization to improve portability

Challenge 3: Complex Networking

Problem: Instances with complex networking configurations can be difficult to migrate.

Solution:

• Document all network interfaces, security groups, and routing tables
• Create network diagrams before migration
• Test network connectivity thoroughly after migration

Best Practices Summary

1. Always back up before migration – Create additional backups beyond the AMI
2. Test in non-production first – Validate the process in a test environment
3. Document everything – Keep detailed records of all steps and configurations
4. Maintain security – Remove sensitive data from AMIs and follow security best practices
5. Plan for rollback – Have a detailed plan to revert changes if necessary
6. Performance testing – Compare performance metrics before and after migration
7. Update documentation – Update system documentation to reflect the new instance configuration

Conclusion

Migrating EC2 instance store-backed instances to different instance types requires careful planning and execution. By following the detailed steps outlined in this guide, you can successfully migrate your workloads while minimizing risks and downtime. Understanding these procedures thoroughly will also help you prepare for questions about instance migration in the AWS SysOps Administrator certification exam.

Remember that AWS continually updates its services and features, so always refer to the latest AWS documentation for the most up-to-date information on migration procedures and best practices.

Additional Resources

• Amazon EC2 Documentation
• Amazon Machine Images (AMI)
• Instance Store-Backed AMIs
• AWS SysOps Administrator Certification