Beyond the Switchover: Using RDS Snapshots to Safely Test MySQL 8.4 Compatibility Before Your Blue/Green Cutover

AWS RDS Blue/Green deployment is a powerful zero-downtime tool, but its Green environment is read-only by design. Here is how to layer a snapshot-based test instance on top of it to validate application compatibility before committing to the full switchover. There is a moment every DevOps engineer, DBA, and SRE dreads: a database engine reaches end-of-life, AWS begins billing you for Extended Support, and the upgrade clock is ticking. For MySQL 8.0, that moment arrived in 2026. AWS began charging Extended Support fees for any RDS instance still running 8.0, and teams across the industry started planning migrations to MySQL 8.4, the current Long Term Support (LTS) release. AWS provides an excellent managed feature for this exact scenario: RDS Blue/Green Deployments. It is powerful, well-documented, and purpose-built for zero-downtime upgrades. But there is a constraint baked into how it works that trips up a lot of engineers the first time they reach for it, and it becomes a