Database Cluster Blue/Green Deployment on Unsupported Instance Type in Aurora MySQL

There are a few options to consider for changing the instance type during a blue/green deployment for an Aurora MySQL cluster:

Take a snapshot of the existing cluster and restore it to a new cluster with the desired instance type. Then perform a switchover to route traffic to the new cluster. This avoids downtime but requires twice the resources during the transition.

Use the AWS Database Migration Service (DMS) to migrate the database from the existing cluster to a new one configured with the target instance type. DMS can minimize downtime during the migration.

If the target instance type is a larger one, scale out the existing cluster by adding instances before performing the switchover. This allows leveraging the existing data without restoring from a snapshot.

For non-production environments, an in-place upgrade is possible by taking an outage during the instance type change. However, this is not recommended for production databases due to the risks.

The best approach would depend on your specific environment and requirements around downtime. AWS documentation provides more details on performing upgrades, migrations and switchovers for Aurora clusters.