Sentinel simple current limiting and degradation demo problem record

The problem record

1. download sentinel-dashboard, After starting with the command line , The console page can be accessed normally , But I add configuration to the project configuration file ：

spring.cloud.sentinel.transport.port=8719
spring.cloud.sentinel.transport.dashboard=localhost:9090

Then keep refreshing the console page , There is no service I registered .

resolvent ：sentinel-dashboard The default is lazy loading mode , Need to add sentinel-dashboard After the configuration , Visit the registered service , Refresh the console page again .

2. In the test sentinel When the number of concurrent threads is controlled , What I set in the rules is 4 individual ：

 List<FlowRule> rules = new ArrayList<>();
        FlowRule rule = new FlowRule();
        rule.setResource(RESOURCE_KEY);
        rule.setCount(4);
        rule.setGrade(RuleConstant.FLOW_GRADE_THREAD);
        rule.setLimitApp("default");
        rules.add(rule);
        FlowRuleManager.loadRules(rules);

Originally, I thought I could only make 4 Threads through , But the printing result is not like this , But sometimes ：

resolvent ：sentinel It is to limit the number of threads accessing resources at that time , That is, when the number of runtime threads accessing resources exceeds the set threshold , Will adopt the set strategy , Directly refuse or something else , The default is to reject directly ; But when the life cycle of a thread that accesses resources ends , New requests can be released , Because my resource method didn't have time-consuming operations or sleep waiting operations, it ended soon , So new threads can access resources .

When writing the case of concurrent thread control number , At first, I wrote as above , But the printing result was unexpected , Because the threshold I set is 4, however thread Variables and set The length of is significantly larger than 4 Of .

Solution ： Put the red box below , That is to say testSleep The following three lines , Put it in entry != null Of if After judging the inside , The print result is right . Because normally, after a thread accessing resources passes , Walk the finally block , Go again testSleep The following three lines , Because at this time, this thread has accessed resources , So the next thread can continue to access , But because this thread is sleep Medium 500 In milliseconds , other 9 Threads are accessible , And soon , therefore set Many times add operation ,500 Milliseconds later remove operation , therefore set.size() The value of 500 Within milliseconds, it approaches 10, Then subtract another .thread It's the same thing .

3. When writing a cold start test case , The rules are set as follows ：

        List<FlowRule> rules = new ArrayList<>();
        FlowRule warmUpRule = new FlowRule();
        warmUpRule.setResource(RESOURCE_KEY);
        warmUpRule.setCount(3);
        warmUpRule.setGrade(RuleConstant.FLOW_GRADE_QPS);
        warmUpRule.setLimitApp("default");
        warmUpRule.setControlBehavior(RuleConstant.CONTROL_BEHAVIOR_WARM_UP);
        warmUpRule.setWarmUpPeriodSec(10);
        rules.add(warmUpRule);
        FlowRuleManager.loadRules(rules);

And the thread that I access resources only creates 3 individual , Originally I expected , There should be no current limit , But the printing result is not like this ：

block It's always worth it , Sometimes it's 1 Sometimes it's 2, I have been unable to understand , The threshold I set is 3, It should all be accessible .

resolvent ： Then I thought of what I set warmUpRule.setControlBehavior(RuleConstant.CONTROL_BEHAVIOR_WARM_UP) This code , It should be set to cold start , The explanation of cold start in the official document is ：

This method is mainly used when the system is at low water level for a long time , When the flow suddenly increases , Directly raising the system to high water level may crush the system in an instant . adopt " Cold start ", Let the flow slowly increase , Gradually increase to the upper limit of the threshold within a certain period of time , Give the cooling system a warm-up time , Avoid crushing the cold system .

So I wonder if ： Although only 3 Threads accessing resources , But the flow increased every time of cold start is 1, So every time there is a finite flow .

After changing the code , It makes sense to find the print result ：

The flow per second is generally increased （ I don't know why it came out 4）, Up to the threshold I set (10), It's stable .

How to increase is not important , It is important to be sure that the traffic is slowly increasing towards the threshold .

4. As if setStrategy and setControlBehavior It can't be used together , After I configured it together, there was a problem ：

The threshold I set is 10, however pass The value of is greater than 10 Of .

resolvent ： Not configured together .

4. In writing, the abnormal proportion is degraded demo When , At first, my code was like this ：

resolvent ： I didn't catch BlockException Out of the exception , I found that the result printed by the console showed that an exception occurred , In a degraded state , But I set the fuse duration to 10s, should 10s Then release one , But until the end ,total,pass,block All are 0;
Later, I tried to catch exceptions , Just find the result .