What changed
On September 4, Google added support for connecting Cloud SQL for SQL Server applications to a write endpoint through the Cloud SQL Auth Proxy and supported language connectors. A write endpoint is a DNS name associated with the writable primary. When a replica failover or switchover changes which instance is primary, Google updates the endpoint so new connections are directed to the new primary. Write endpoints were already available; the material change is that applications using Google’s supported connector/proxy layer can now use that abstraction directly instead of separately discovering or pinning an instance address.
Why it matters
High-availability databases only help if applications can find the new primary reliably. Hard-coded instance endpoints create an extra failure mode during switchover and make connection logic more complicated. Connector support makes the write endpoint a more complete application boundary for Cloud SQL SQL Server. It does not make failover invisible: existing connections can still break and applications need sensible retry behavior, but it reduces the amount of topology knowledge the application must carry.
The connector path can now target the role, not the instance
Cloud SQL Auth Proxy and supported language connectors can be configured with the write-endpoint DNS name. That shifts the connection target from a specific database instance to the current writable role.
Failover changes the primary behind the endpoint
When Cloud SQL promotes a replica during failover or a planned switchover, the write endpoint is redirected to the new primary. New connections using that name can therefore follow the topology change without an application configuration rewrite.
This does not remove normal database failover behavior
A DNS-backed endpoint does not preserve an already-open connection through a primary transition. Applications should still expect transient connection failures and use retry/backoff patterns appropriate to their transaction semantics.