SpringCloudAlibaba Sentinel (flow control rules)

What is Sentinel

A lightweight cloud native microservice oriented traffic control component.


Sentinel is mainly divided into two parts

• Core library: Java client, which does not depend on any framework, can run all Java runtime environments, as well as Dubbo / spring cloud and other frameworks
  There is also good support.

• Console: Dashboard is developed based on SpringBoot and can be run directly after packaging without additional application containers such as Tomcat.

Download and installation of Sentinel

Download address:
https://github.com/alibaba/Sentinel/releases
Select version

The download is a jar package, which can be run as long as there is a java running environment on the computer
Start Sentinel

Build demonstration cases

Create a new cloudalibaba-sentinel-service8401 model

1. New model
   

2. Change pom

   <dependencies>
       <!--SpringCloud alibaba sentinel-datasource-nacos: For subsequent persistence-->
       <dependency>
           <groupId>com.alibaba.csp</groupId>
           <artifactId>sentinel-datasource-nacos</artifactId>
       </dependency>
       <!--SpringCloud alibaba Sentinel-->
       <dependency>
           <groupId>com.alibaba.cloud</groupId>
           <artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
       </dependency>
       <!--openFeign-->
       <dependency>
           <groupId>org.springframework.cloud</groupId>
           <artifactId>spring-cloud-starter-openfeign</artifactId>
       </dependency>
       <!--spring cloud alibaba nacos-->
       <dependency>
           <groupId>com.alibaba.cloud</groupId>
           <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
       </dependency>
       <!--web/actuator These two are generally used together and written together-->
       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-web</artifactId>
       </dependency>
       <!--monitor-->
       <dependency>
           <groupId>
               org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-actuator</artifactId>
       </dependency>
       <dependency>
           <groupId>org.projectlombok</groupId>
           <artifactId>lombok</artifactId>
           <optional>true</optional>
       </dependency>
       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-test</artifactId>
           <scope>test</scope>
       </dependency>
   </dependencies>
   

3. Change yml

   server:
     port: 8401
   
   spring:
     application:
       name: cloudalibaba-sentinel-service
     cloud:
       nacos:
         discovery:
           # Nacos service registry address
           server-addr: xxxxxx:8848
       sentinel:
         transport:
           # Configure Sentinel dashboard address
           dashboard: localhost:8080
           # The default port is 8719. If it is occupied, it will automatically start a + 1 scan from 8719 until the occupied port is found.
           port: 8719
   
   management:
     endpoints:
       web:
         exposure:
           include: "*"
   

4. Business class
   

5. Start Sentinel and demo model and test

• To display the started demo class in Sentinel visual interface, you must access the controller business once before displaying it (lazy loading mechanism)
  

Flow control rules

Noun analysis

Test effect
QPS + direct + fast failure


When the number of accesses per second is greater than 2, the failure page is displayed directly

Number of threads = 1

Number of threads 1: only one api: / testA request can be processed at a time. When the number of threads calling the api reaches the threshold, the flow is limited

Flow control mode - correlation

When testB, the resource associated with testA, reaches the threshold value, it limits the current

Flow control mode - link
Link flow control mode means that when the resources from an interface reach the current limit condition, the current limit is turned on

Flow control effect

• Quick failure: direct failure, exception thrown: Blocked by Sentinel(flow limiting)

• Warm Up: Warm Up, that is, when a large number of requests call suddenly, a buffer time will be given
  
  That is, preheat for 5s. The threshold in this 5s is the threshold divided by coldFactor (3 by default) = 3. The real threshold will not be reached until the preheating time is long

• Queue up
  When the threshold is exceeded, don't refuse directly and let them queue up
  
  Failure occurs when the queue exceeds the timeout