Azure App Service and Azure SQL Database: Zero-Downtime Migration Interoperability

Migrating a small application to a new version while maintaining availability often involves using Azure App Service deployment slots in conjunction with an Azure SQL Database. The goal is to utilize the swap operation to redirect traffic from a staging slot to production without dropping active requests.

While the swap operation handles the routing transition, the interoperability between the application versions and the database layer introduces constraints. Specifically, if the migration requires database schema updates, both the production and staging versions must coexist and function against the same database instance during the warm-up and transition phase.

There is uncertainty regarding the behavior of active connections and the precise timing of the traffic shift relative to the application's startup latency.

• How does the App Service swap operation handle existing TCP connections to the Azure SQL Database during the transition window?
• What is the mechanism for ensuring the production slot does not experience timeouts if the staging slot's warm-up period exceeds the default timeout thresholds?