[micro service ~sentinel] sentinel degradation, current limiting, fusing

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Column introduction

【 Microservices ~Sentinel】 At present, it mainly updates micro services , Learn together and progress together .

Introduction to this issue

This issue focuses on Sentinel

List of articles

Common concepts of microservices

Service avalanche

Service failure

service degradation

The difference between fusing and degradation

Sentinel Introduce

core Downgrade

The phenomenon 1

The phenomenon 2

Degraded operation

Common concepts of microservices

Official website ：quick-start

Service avalanche

• Service avalanche ： In the service of the whole link , A service failure , A situation in which the service of the entire link fails .

1. There is a whole link service （Service A、Service B、Service C）

2. Service A The flow suddenly increases , Lead to Service B and Service C Flow also increases .

3. Service C Because I couldn't resist the request , Become unavailable . Lead to Service B Your request becomes blocked .

4. When Service B Our resources are exhausted ,Service B It becomes unavailable .

5. Last Service A Unavailable .

Service failure

• Service failure ： When the downstream service for some reason suddenly Become unavailable or Response is too slow , Upstream services ensure the availability of their overall services , The target service is no longer invoked , Go straight back to , Rapid release of resources . If the condition of the target service improves, the invocation is resumed .

1. In the beginning closed state , Once the detected error reaches a certain threshold , switch open state ;

2. There's going to be one reset timeout, It's about time , Will shift to half open state ;

3. Attempt to release part of the request to the back end , Once the detection is successful, the regression closed state , Recovery service ;  

service degradation

• What is service degradation ？

  • When the downstream service for some reason Response is too slow , Downstream services actively shut down some of the less important services , Free up server resources , Increase response speed ！

  • When the downstream service for some reason Unavailable , The upstream actively invokes some local degradation logic , Avoid caton , Quickly return to the user ！

The difference between fusing and degradation

• The difference between service fusing and service degradation ？

  • There are many ways to downgrade a service ！ Such as switching down 、 Current limiting the drop 、 Fusing the drop !

  • Service circuit breaker is one of the demotion modes ！

  • Happen when The downstream service is not available The situation of , Circuit breakers and downgrades must go together .

• Service degradation is mostly a business-level process , Fusing is a framework level implementation

• Switch the drop

  Configure a switch in the configuration center ( Variable ), Change the switch in the configuration center , Decide which services to downgrade

Sentinel Introduce

• Sentinel ： A highly available flow control and protection component , Ensure the stability of micro Services .

• Sentinel In two parts ,sentinel-core And sentinel-dashboard.

  • sentinel-core Some can support local introduction sentinel-core Integrate and configure the flow restriction rules .

  • sentinel-dashboard It's in core It can support the maintenance and adjustment of online flow control rules and circuit breaker rules .

core Downgrade

The phenomenon 1

• Providers build clusters （8170/8270）, The caller calls , At this point, close a service of the provider （8270）

• Existing phenomenon ： visit 8170 Successful visit , Cannot access 8270

  • Slightly Caton , Just a moment later , No longer stuck .

The phenomenon 2

• Providers build clusters （8170/8270）, The caller calls , At this point, close all services of the provider

• The phenomenon ： cannot access

Degraded operation

Add coordinates

<dependency>
    <groupId>com.alibaba.cloud</groupId>
    <artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
</dependency>

modify yml file , Turn on feign Yes sentinel Support for

feign:
  sentinel:
    enabled: true

  Modify the startup class , Turn on feign

package com.czxy;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.openfeign.EnableFeignClients;


@SpringBootApplication
@EnableDiscoveryClient  // Service discovery 
@EnableFeignClients     // The remote invocation 
public class TestNacosConsumerApplication {
    public static void main(String[] args) {
        SpringApplication.run(TestNacosConsumerApplication.class, args );
    }
}

  modify Feign Realization

package com.czxy.feign;

import org.springframework.stereotype.Component;

@Component
public class EchoFeignFallback implements EchoFeign {
    @Override
    public String echo(String string) {
        return " Degraded processing ：" + string;
    }
}

package com.czxy.feign;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;


// @FeignClient(value = " service name ", path = "controller Configured path " )
@FeignClient(value = "service-provider", fallback = EchoFeignFallback.class )
public interface EchoFeign {

    //  And  nacos-provider-2.1>EchoController The declared method is completely consistent 
    @GetMapping("/echo/{string}")
    public String echo(@PathVariable String string);
}

Close service provider , test

• Be careful ： Need to restart service