What is the service instance
The cloud server instance (ECS instance) is a virtual computing environment that contains the most basic computing components, such as CPU, memory, operating system, bandwidth, and disk. You can interpret an ECS instance as a stand-alone virtual machine. ECS instance is the core concept of cloud server, and other resources, such as disk, IP, mirror, snapshot and so on, can only be used when combined with ECS instance.
What is a free zone
A usable area is a physical region in which electricity and networks are independent of each other. An ECS instance network latency in the same usable area is smaller.
In the same region between the available area and the available area intranet interoperability, can be isolated between the available areas of fault isolation. Whether the cloud server ECS instance is placed in the same usable area is mainly determined by the requirements for disaster tolerance and network latency.
If your application requires a high disaster recovery capability, it is recommended that you deploy the cloud server ECS instance to a different available area in the same region;
If your application requires a lower network latency between instances, it is recommended that you create an ECS instance in the same available zone.