AWS Cross Account Migration Guide for Secure and Scalable Workloads

Introduction

Migrating workloads from one AWS account to another may seem straightforward, but in real-world environments, it involves much more than simply copying resources. A successful migration depends heavily on pre-migration prerequisites, access validations, licensing checks, encryption dependencies, and service compatibility. If these prerequisites are not met, migration can fail in the middle, causing downtime, unexpected costs, compliance risks, and operational delays.

Overview

This blog covers the critical prerequisites for an AWS account-to-account migration and highlights the major issues teams typically face when these checks are missed.

1. AWS IAM Access and Cross-Account Permissions

Key prerequisites

• Validate cross-account AWS IAM roles and trust policies
• Ensure least-privilege permissions for migration activities
• Verify access to services like Amazon EC2, Amazon RDS, Amazon S3, AWS IAM, AWS KMS
• Confirm CLI / SDK authentication from migration tools

Before starting migration, the most important step is to establish secure cross-account access. The source and target accounts must have properly configured AWS IAM roles with trust relationships. Missing permissions often cause failures when copying AMIs, snapshots, Amazon S3 objects, Amazon RDS snapshots, or AWS KMS-encrypted resources.

A common issue when this is not validated is:

• AccessDeniedException
• UnauthorizedOperation
• Snapshot copy failures
• Inability to assume cross-account roles

2. AMI and Amazon EC2 Migration Readiness

Key prerequisites

• Validate whether AMIs are custom or marketplace-based
• Check OS support lifecycle
• Verify AMI sharing permissions
• Confirm snapshot access and dependencies

While AMIs can be shared across accounts, AWS Marketplace AMIs have additional licensing and subscription requirements. For shared AMIs, the target account must explicitly have launch permissions, and if the backing snapshots are encrypted, the corresponding AWS KMS keys must also be shared.

3. AWS KMS Encryption Dependencies

Key prerequisites

• Identify all encrypted resources
• Validate AWS KMS key ownership
• Share customer-managed keys across accounts
• Update key policies

This is one of the biggest migration blockers. Many AWS resources are encrypted using KMS. If the target account does not have access to the AWS KMS key, the migration will fail. For example, AWS specifically requires AWS KMS permissions when sharing encrypted AMIs. Default AWS-managed keys cannot be used for cross-account AMI sharing.

Common errors include:

• AWS KMS Access Denied
• Snapshot copy failed
• Unable to decrypt resource

4. Networking and VPC Dependencies

Key prerequisites

• Map all Amazon VPCs and subnets
• Identify public/private subnet architecture
• Validate route tables and NAT gateways
• Review security groups and NACLs

Many migrations fail after resource creation because networking is not recreated properly. Even if the Amazon EC2 migration succeeds, workloads may still fail because:

• subnet CIDR overlaps
• route tables missing
• IGW / NAT not attached
• security groups not replicated

This causes application outages post-migration. Networking prerequisites should always be captured before migration begins.

5. DNS and Certificate Migration

Key prerequisites

• Export all Amazon Route 53 hosted zone records
• Recreate or validate ACM/SSL certificates
• Prepare a DNS cutover and rollback plan

DNS migration is often treated as a final step, but it should be planned well in advance. Even if the application infrastructure is fully migrated, users will not be able to access it if DNS records are missing or incorrectly configured. A common issue is forgetting to migrate A, CNAME, MX, and TXT records, especially validation records used for SSL certificates. This can break website access, email routing, and third-party integrations.

Another major challenge is certificate validation. Certificates issued through Amazon Web Services Certificate Manager are region- and account-specific, so they must be reissued or revalidated in the target account before DNS cutover.

6. Database Migration Dependencies

Key prerequisites

• Verify database engine and version compatibility
• Check subnet groups and security groups
• Validate snapshot restore permissions and encryption

Database migration requires more than just copying snapshots. The target account must support the same database engine version, storage type, and parameter configurations used in the source account.

One common issue occurs when restoring snapshots into an environment where the DB subnet group or parameter group does not exist. In such cases, the restore process fails even though the snapshot copy succeeds. Encrypted databases introduce an additional dependency on AWS KMS permissions. If the key is not shared properly, snapshot restore operations will fail, leading to delays during cutover.

7. Marketplace and Third-Party Licensing

Key prerequisites

• Identify all AWS Marketplace dependencies
• Validate license subscription in the target account
• Check product support lifecycle

This is one of the most overlooked areas during migration planning. AMIs or appliances purchased through AWS Marketplace are licensed per account, which means the target account must separately subscribe and accept the terms.

As you experienced with CentOS, simply sharing the AMI is not always enough. The target account may throw launch errors until the marketplace subscription is completed. Another major concern is deprecated products. Migrating a workload running on an unsupported OS or third-party image may address the short-term migration need, but it creates future operational and security risks.

8. Backup and Rollback Strategy

Key prerequisites

• Create AMI and snapshot backups
• Export database backups before cutover
• Document rollback steps and ownership

Every migration should include a tested rollback plan. If something goes wrong after cutover, the team must be able to restore services quickly without impacting production users. A common issue is proceeding with migration without verified backups. In such cases, migration failures can result in extended downtime and potential data loss. Rollback planning should clearly define who is responsible, which resources need to be restored, and the estimated recovery time so that business teams can plan accordingly.

Conclusion

Drop a query if you have any questions regarding Migration, and we will get back to you quickly.