# High Availability Characteristics Of Placement Driver Servers

+ The leader node provides all services, and the follower is standby
+ Rely on embedded etcd to implement leader elect
+ Requirements for consistency
  + Assign a strictly monotonically increasing timestamp
  + There can only be one leader at a time


![left](./student-guide/diagram/28-PD-High-availability-feature-01-01.png)

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Single point of the entire system
 The leader node provides all services, and the follower is standby
Requirements for consistency
Assign a strictly monotonically increasing timestamp
There can only be one leader at a time
Rely on embedded etcd to implement leader elect
Raft
lease
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