A. Create a customer-managed CMK in the centralized account. Allow other applicable accounts to use that key for cryptographical operations by applying proper cross-account permissions in the key policy. Create an IAM role in all applicable accounts and configure its access policy to allow the use of the centrally managed CMK for cryptographical operations. Configure EC2 Auto Scaling groups within each applicable account to use the created IAM role to launch EC2 instances.
B. Create a customer-managed CMK in the centralized account. Allow other applicable accounts to use that key for cryptographical operations by applying proper cross-account permissions in the key policy. Create an IAM role in all applicable accounts and configure its access policy with permissions to create grants for the centrally managed CMK. Use this IAM role to create a grant for the centrally managed CMK with permissions to perform cryptographical operations and with the EC2 Auto Scaling service-linked role defined as the grantee principal.
C. Create a customer-managed CMK or an AWS managed CMK in the centralized account. Allow other applicable accounts to use that key for cryptographical operations by applying proper cross-account permissions in the key policy. Use the CMK administrator to create a CMK grant that includes permissions to perform cryptographical operations that define EC2 Auto Scaling service-linked roles from all other accounts as the grantee principal.
D. Create a customer-managed CMK or an AWS managed CMK in the centralized account. Allow other applicable accounts to use that key for cryptographical operations by applying proper cross-account permissions in the key policy. Modify the access policy for the EC2 Auto Scaling roles to perform cryptographical operations against the centrally managed CMK.