Alibaba Cloud provides cloud computing services in nearly 20 regions around the world. Each region contains multiple zones. The zones in the same region are designed to have an extremely low mutual network latency (less than 3 ms) and to be fault isolated units.
A single-zone master instance of RDS runs on two physical servers, with the cabinets, air conditioners, electricity, and networks in redundant mode. Through asynchronous and semi-synchronous data replication and efficient HA switchover, RDS provides database availability that is impossible with only physical servers.
To provide even higher availability than single-zone instances, RDS supports multi-zone instances. A multi-zone instance runs on physical servers deployed in different zones (such as Zone A and Zone B). When Zone A fails, traffic can be quickly switched to Zone B. The entire failover is transparent to users and requires no application code changes.
Note: The connection between applications and the database is interrupted during the failover. Applications must reconnect to the database.