Differences between different registries

# 1.CAP Theorem
- CAP Theorem ：CAP The theorem is also called CAP principle , In a distributed system , Uniformity （Consistency）、 Usability （Availability）、 Partition tolerance （Partition tolerance）.CAP Principle means , These three elements can only achieve two points at most , It's impossible to combine the three .
    ` Uniformity （C）： All data backup in distributed system , Is it the same value at the same time .（ Equivalent to all nodes accessing the same copy of the latest data ）
    ` Usability （A）： After some nodes in the cluster fail , Whether the cluster as a whole can respond to the client's read and write requests .（ High availability for data updates ）
    ` Zone tolerance （P）, It's high availability , A node collapsed , Does not affect other nodes （100 Nodes , A few , No impact on Service , The more machines, the better ）
    
# 2.Eureka characteristic
- Eureka No strong data consistency algorithm is used to guarantee the data consistency between different clusters Server The data are consistent , Strive for the final consistency of registry data only through data copy , Although we give up the strong consistency of data, we get Server The usability of , It reduces the cost of registration , It improves the robustness of cluster operation .

# 3.Consul characteristic
- be based on Raft Algorithm ,Consul Provide strong consistency of registry services , But because of Leader The node undertakes all the processing work , It will increase the cost of registration and discovery , Reduced service availability . adopt Gossip agreement ,Consul It can be monitored very well Consul Cluster operation , At the same time, it is convenient to notify all kinds of events , Such as Leader Selection occurs 、Server Address change, etc .

# 4.zookeeper characteristic
- be based on Zab agreement ,Zookeeper It can be used to build a service registration and discovery center with strong data consistency , In contrast, it sacrifices the availability of services and improves the time required for registration .