Sentinel Entry use

1. The concept

1.1 what is

Sentinel colloquially refers to it as the upgraded Web version of Hystrix. Through the way of visualization, solve the service in practice encountered various problems.

1.2 Download and Installation

Download the latest stable JAR file and start it.

• windowBackground Startup Modejavaw -jar xxx.jar ,cmdWindow to startjava -jar xxx.jarThe default boot port is 8080. If port 8080 is used, you can customize the boot portjava -jar xxx.jar --server.port=8888
• linuxBackground Startup Modenohup java -jar xxx.jar >log.log &Specify log file location and background suspend startup.

Address to access after successful startup:http://ip:portThe default user name and password aresentinel.

1.3 Core function modules

• Service avalanche
• Service degradation
• Service fusing
• Service current limiting

1.4 Used in the project

Add the following configuration to the service configuration file

spring:
  cloud:
    nacos:
      discovery:
        server-addr: 192.16810.120.: 8848 The nacOS registry is used here. The actual configuration is based on the registry of your own project
    sentinel:
        transport:
            dashboard: 192.168101.120.: 8080 # start address above
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2. Actual application and configuration

2.1 Panel terminology

2.2 Configuration Instructions

2.2.1 Threshold Type QPS Flow control mode Direct

Description of related parameters and methods

Sentinel provides this capability, which allows us to define another method to return data instead of the restricted or exception service, namely fallback and blockHandler

• fallback: Fails to be invoked. If unknown exceptions occur on the interface, the interface is invokedfallbackSpecifies the interface.
• blockHandler:sentinelCalled if the access is restricted or the service is degradedblockHandlerSpecifies the interface.

1. The test ofservicelayer

/** * Threshold type QPS flow control mode direct */

    String hello(String limit);

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2. serviceImplementation layer

    @SentinelResource(value = "limit",defaultFallback = "defaultFallback",blockHandler = "handlerException",blockHandlerClass = {BlockException.class})
    @Override
    public String hello(String limit) {
        return "Threshold type QPS Flow control mode direct";
    }
    
    // Customize simple service limiting or downgrade callback methods
    public String defaultFallback(a){
        return "Too crowded ~ please try again later";
    }
    public String handlerException(a){
        return "Tests whether the portion that exceeds the traffic limit enters the blockHandler method.";
    }

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3. controllertest

    @Autowired
    private SentinelService sentinelService;

    @GetMapping("/test1")
    public String testA(a){
        return "this is testA -----------";
    }

    @GetMapping("/test2")
    public String testB(a){
        return "this is testB -----------";
    }

    @GetMapping("/limit")
    public String limit (a){
        return sentinelService.hello("Test QPS current limiting");
    }
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4. Call the above three test interfaces in turn, becauseSentinelService monitoring is lazily loaded. Only when the service interface is called, it is captured by the monitoring center. After the call, the following data can be seen in the panel

5. Configure flow control for interfaces of related services as follows: (If the current interface attempts more than three times within 1s, the flow limiting operation is triggered directly and the callback method fails.)

6. Test, get use in browserpostmanQuick click interfacehttp://localhost:8041/limit, when more than three times within 1s, enter the preset callback method and return the parameter as

2.2.2 Threshold Type Number of threads and flow control mode Direct

1. servicelayer

String threadTest(String thread);
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2. serviceImplementation layer

    @SentinelResource(value = "thread",defaultFallback = "defaultFallback",blockHandler = "handlerException",blockHandlerClass = {BlockException.class})
    @Override
    public String threadTest(String thread) {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "Threshold type thread count, flow control mode direct";
    }
    

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3. controllerlayer

    @GetMapping("/thread")
    public String thread(a){
        return sentinelService.threadTest("Thread test");
    }
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4. useApache jmeterRun multithreaded tests

Create 5 threads and test normally. Each thread results return normally, add thread limit flow limiting configuration

5. Set the thread threshold to 4, create 5 threads to call the interface, from the return result can be seen, the first four threads return normal results, there is a thread return is restricted results

2.2.3 Association between threshold Type QPS and Flow Control Mode

1. Based ontest1andtest2The interface remains unchanged. Associate the two interfaces.
2. Simulation scenario: Payment interface and order interface. When the payment interface reaches the threshold, the generation of order interface will be limited. Relieve pressure on services. The specific process is as follows

3. Test interface, separate fast and slow testtest1andtest2Interface. The returned result is normal. 4postmanandJmeterTest two interfaces to create multiple thread runstest2At the same timepostmancalltest1To trigger traffic limiting and return an exception log. whentest2After limiting the current,test1The interface returns normally

2.2.4 Flow control effect

1. Fail fast

   Fail directly and enter exception handling, or enter the specified callback and do no additional processing.

2. Warm Up Enters a buffering phase from the start to the maximum threshold. The threshold is 1/3 of the maximum threshold at the beginning, and then increases slowly until the maximum threshold is reached. It is applicable to the sudden increase of traffic and changes to a slow increase, avoiding the server downtime caused by sudden large traffic.

Note: For example, if the threshold is set to 10, the initial maximum allowed number of requests is 10/3=3. When a large number of requests occur again, the threshold is automatically increased from 3 to 10 within 5 seconds

3. Waiting in line

Set the threshold type to QPS. Set the single-node threshold to 2 and the flow control effect to queuing. Implementation effect for 1 s, the current interface to request more than 2, then the rest of the not directly in abnormal, into the queue, waiting in front of the interface call completed will continue to call the back of the interface, also can set the timeout, if didn’t call out more than the current time, the interface directly behind the discarded into the exception

Create 10 thread test interfaces with JMeter. Set the thread interval to 0.4s and the timeout time to 2000ms. Only a small part of the request will be limited and the rest will execute slowly.

2.2.5 Fuse downgrade

Reference books Jane at https://www.jianshu.com/p/35ba0d96450d