sentinel documents summarized in the internship

Official documents: https://sentinelguard.io/zh-cn/docs/dashboard.html

1. Characteristics

Sentinel vs. Hystrix

	Sentinel	Hystrix
Isolation strategy	Based on Concurrency	Thread pool isolation / semaphore isolation
Fuse degradation strategy	Based on response time or failure rate	Based on failure ratio
Real time index realization	sliding window	Sliding window (based on RxJava)
Rule configuration	Support multiple data sources	Support multiple data sources
Expansibility	Multiple extension points	Form of plug-in
Annotation based support	Coming soon	support
Call link information	Support synchronous call	I won't support it
Current limiting	Based on QPS / concurrency number, current limiting based on call relationship is supported	I won't support it
Flow shaping	Support slow start and homogenizer mode	I won't support it
System load protection	support	I won't support it
Real time monitoring API	every kind of	Relatively simple
Console	Out of the box, you can configure rules, view second level monitoring, machine discovery, etc	imperfect
Adaptation of common frames	Servlet, Spring Cloud, Dubbo, gRPC, etc	Servlet,Spring Cloud Netflix

2. Download and use

Download sentinel console jar package address: https://ithub.com/alibaba/Sentinel/releases

Start sentinel through java -jar. The default port occupied by sentinel is 8080. If there is a need to change the port, change the corresponding port. Change here to 18080.

Start the command line in the jar package directory and run:

java -Dserver.port=18080 -jar  sentinel-dashboard-1.8.0.jar 

Visit localhost: 18080 to open the local console.

From sentinel 1.6 Since 0, sentinel console has introduced basic login function. The default user name and password are sentinel.

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3. Basic configuration

Join dependency management and dependency

<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>

		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-dependencies</artifactId>
			<version>Hoxton.SR8</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>

		<!--springCloud-Alibaba-->
		<dependency>
			<groupId>com.alibaba.cloud</groupId>
			<artifactId>spring-cloud-alibaba-dependencies</artifactId>
			<version>2.2.1.RELEASE</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>

		<!--sentinel Current limiting-->
		<dependency>
			<groupId>com.alibaba.cloud</groupId>
			<artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
			<version>2.2.1.RELEASE</version>
		</dependency>

		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-openfeign</artifactId>
			<version>2.2.2.RELEASE</version>
		</dependency>
	</dependencies>

Note that you can modify the port and other corresponding information. Here sentinel uses the self-defined 18080 port

server:
    port: 8080
spring:
    application:
      name: sentinel-demo
    cloud:
      sentinel:
        transport:
          dashboard: 127.0.0.1:18080
        eager: true
        datasource:
          ds1:
            file:
              file: classpath:flowrule.json
              data-type: json
              rule-type: flow
          ds2:
            file:
              file: classpath:degraderule.json
              data-type: json
              rule-type: degrade

Startup class

@SpringBootApplication
public class SentinelMainApplication {

	public static void main(String[] args) {
		SpringApplication.run(SentinelMainApplication.class, args);
	}

}

Controller class requiring flow control, sample code

@RestController
public class DemoController {
   
    @GetMapping("/hello")
    public String hello() {
        return "hello";
    }

    @GetMapping("/resource")
    @SentinelResource(value = "test-resource", blockHandlerClass = {ExceptionUtil.class}, blockHandler = "exHandler")
    public String resource() {
        return "resource";
    }
}  

Startup class

It should be noted that sentinel is a lazy loading mechanism, which also means that you need to access some / hello in the above Controller to see the service in the sentinel background
Browser access http://localhost:8080//hello

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Then refresh the sentinel background http://localhost:18080/#/dashboard/home

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Monitoring of / hello has occurred.

4. Project structure

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1.DemoController.java: used to test url flow restriction, association mode and flow restriction by resource name

2.ConfigDemoController.java: test file mode rule persistence

3.DegradeController: fuse degradation test

4.ParamController.java,SecurityController.java: black and white list function test

5.DemoUrlBlockHandler.java: intercept information customization

6.ExceptionUtil.java: prompt method collection class for intercepting resource requests

7.flowrule.json: store local flow control rules

8.sentinel-dashboard-1.8.0.jar: sentinel console jar package.

5. Flow control

Direct mode

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Add a flow control rule to control the flow of / hello port, and set the maximum access times per second 2; The default mode here is direct mode, quick failure, and advanced options are selected for other modes.

Quickly visit / hello to see the results.

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The default interception information of the system can also be customized:

Create demourlblockhandler. config package java

@Component
public class DemoUrlBlockHandler implements BlockExceptionHandler {
    @Override
    public void handle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, BlockException e) throws Exception {
        httpServletResponse.getWriter().println("flow is limiting");
    }
}

Association mode

Add a flow control rule and open advanced options:

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Add DemoController under Controller package:

 @GetMapping("/helloA")
    public String helloA() {
        return "helloA";
    }

Test:

Use postman to simulate the dense access / helloA interface, set 20 threads to access every 0.3 seconds.

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View the related resources: / hello.

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Note: when the QPS threshold of the associated resource / hello a exceeds 1, access to / hello is restricted.

Link mode

1. Under the cluster node link, view that the resource entry of / hello is sentinel_spring_web_context ;

2. Add flow control and configure the link entry resource as sentinel_web_servlet_context ;

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3. When frequently accessing the interface / hello, an error flow is limiting is found, indicating that the flow is limited.

Limit current by resource name

@SentinelResource annotation: it is used to define resources and provides AspectJ extension for automatically defining resources and handling blockexceptions;

Add the following code to DemoController:

 @GetMapping("/resource")
 @SentinelResource(value = "test-resource", blockHandlerClass = {ExceptionUtil.class}, blockHandler = "exHandler")
    public String resource() {
        return "resource";
    }

Define resource name: Test Resource

Add flow control rule by resource name:

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Quick access / resource:

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6. Rule persistence

Once we restart the application, Sentinel rules will disappear, and the production environment needs to persist the configuration rules.

Local file persistence rules are used here.

1. Add yml configuration:

 datasource:
          ds1:
            file:
              file: classpath:flowrule.json
              data-type: json
              rule-type: flow

2. Create a new json saving rule with the same name under resource:

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3. Write rules:

[
  {
    "resource": "file-resource",
    "controlBehavior": 0,
    "count": 1,
    "grade": 1,
    "limitApp": "default",
    "strategy": 0
  },
  {
    "resource": "test-resource",
    "controlBehavior": 0,
    "count": 1,
    "grade": 1,
    "limitApp": "default",
    "strategy": 0
  }
]

• Resource: resource name, that is, the object of the flow restriction rule
• count: current limiting threshold
• grade: current limiting threshold type (QPS or number of concurrent threads)
• limitApp: the call source of flow control. If it is default, the call source will not be distinguished
• Strategy: call relationship flow limiting strategy
• controlBehavior: flow control effect (direct rejection, Warm Up, uniform queuing)

4. Start the service. Open the console.

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7. Fuse degradation

Create a DegradeController and test it when an exception is generated.

public class DegradeController {
    int i=0;
    @GetMapping("/testD")
    public String message1() {
        i++;
        // The abnormal ratio is 0.333
        if (i % 3 == 0) {
            throw new RuntimeException("Simulation anomaly");
        }
        return "degrade is testing";
    }

New downgrade rule:

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When the exception ratio is greater than 0.25, the request per second is greater than or equal to 1; The degradation rule takes effect, the fuse duration is 10 seconds, and it returns to normal after 10 seconds.

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Fuse comparison with Hystrix:

The thread pool isolation commonly used by Hystrix will cause a large overhead of thread up and down switching; The semaphore isolation used by Hystrix controls the concurrency of a resource call. The effect is good, but it cannot automatically degrade slow calls;

Sentinel provides semaphore isolation through the flow control of the number of concurrent threads; In addition, sentinel supports more fuse degradation dimensions, can flow control and fuse a variety of indicators, and provides real-time monitoring and control panel, which is more powerful.

}

New downgrade rule:

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When the abnormal proportion is greater than 0.25，Requests greater than or equal to 1 per second; The degradation rule takes effect, and the fusing time is 10 seconds,10 Return to normal in seconds.

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**And Hystrix Fusing comparison of:**

Hystrix Common thread pool isolation will cause threads to switch up and down overhead Relatively large; Hystrix The semaphore isolation is used to control the concurrency of a resource call. The effect is good, but the slow call cannot be automatically degraded;

Sentinel The function of semaphore isolation is provided through the flow control of the number of concurrent threads; In addition, Sentinel It supports more fuse degradation dimensions, can flow control and fuse a variety of indicators, and provides real-time monitoring and control panel, which is more powerful.