Working principle of sentinel series (concept)

Sentinel The core function of is mainly divided into three parts ： Workflow 、 Data structure and current limiting algorithm , The architecture is as follows ：

Pictured above , We can see that , The call link is Sentinel The main work flow of , It's made up of all kinds of Slot Of slots , Will be different Slot String together in a certain order ( In fact, it is the responsibility chain model ), So as to combine different functions , The function mentioned here is mainly current limiting 、 Downgrade 、 System protection ,Sentinel Each slot in the Slot All have different responsibilities , such as ：LogSlot, Just look at the name , This slot is responsible for logging ,FlowSlot Is responsible for current limiting, etc , Responsibilities are relatively separated , Each module focuses on maintaining a function

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stay Sentinel in , In fact, all resources have corresponding resource names , That is to say resourceName, Each time a resource is accessed, a corresponding Entry object , Creating Entry Colleague , A series of functional slots will also be created (slot chain), These slots form a chain of responsibility , And each has a different responsibility , As follows ：

1、NodeSelectorSlot： Collect the call path of resources , Store call stack in dressing structure , It is used to limit current and degrade according to the calling path

2、ClusterBuilderSlot： It is responsible for creating cluster nodes with resource name dimension statistics ClusterNode, Create each level ClusterNode Press call source prigin The division of StatisticNode

3、LogSlot： In case of current limiting 、 Fuse 、 Be responsible for recording logs during system protection

4、AuthoritySlot： Access control , Support blacklist and whitelist strategies

5、SystemSlot： Control the total inlet flow , The limiting conditions are, in turn, total QPS、 Bus number 、RT threshold 、 The operating system is currently load、 The operating system is currently CPU utilization

6、FlowSlot： According to the current limiting rules and each Node Current limiting judgment shall be conducted for the same level data in

7、DegradeSlot： According to the fusing rules and each Node Service degradation based on the statistics in

8、StatisticSlot： Count the number of requests from different dimensions 、 Passing number 、 Current limiting number 、 Number of threads, etc runtime Information , These data are stored in DefaultNode、OriginNode and ClusterNode in