How to Use

• Introduction

• Define Resource

  • "try" and "catch" Mode
  • Bool Mode

• Define Rules

  • Definitions of Rule
  • HTTP Commands for Rules
  • Integrate with rule repositories

Introduction

To use Sentinel, you only need to complete 2 steps:

1. Define resources
2. Define rules

These two steps don’t have to be synchronized. As long as the resources are defined, you can add rules as needed. Multiple rules can be applied to the same resource simultaneously.

Sentinel provides adaptions to popular frameworks as well. After introducing these adapters, services and methods provided by these frameworks are defined as resources by default.

Define Resource

"try" and "catch" mode

  Entry entry = null;
  try{   
      entry = SphU.entry("hellowrold");
    /**
    * code logic
    */
  } catch (BlockException e1) {
    //resource is rejected
    /**
    * logic to handle exception
    */
  }finally{
    if(entry != null){
      entry.exit();
    }
  }
}

Bool Mode

  if(SphO.entry("helloworld")){
    try {
      /**
      * code logic
      */
    } finally {
      SphO.exit();
    }
  }else{
    //resource is rejected
    /**
    * logic to handle exception
    */
  }
}

Adapters to Popular Frameworks

For details, please refer to Adapters to popular frameworks.

Define Rules

Sentinel provides APIs for you to modify your rules, which can be integrated with various kinds of rule repository, such as configuration server and SQL.

Definition of Rules

There are 3 types of rules：flow control rules, circuit breaking rules, and system protection rules.

Flow control rule (FlowRule)

Definition:

key fields：

Field	Description	Default value
resource	resource name, defined in entry()
count	threshold
grade	calculated by QPS or concurrent thread count	QPS
limitApp	refer to specified caller	default
strategy	by resource itself or other resource (refResource)，or entry (refResource)	resource itself
controlBehavior	reject directly，queue，slow start up	reject directly

Multiple rules can be applied to the same resource.

API

API:FlowRuleManager.loadRules() can be used to configure flow control rules.

private static void initFlowQpsRule() {
        List<FlowRule> rules = new ArrayList<FlowRule>();
        FlowRule rule1 = new FlowRule();
        rule1.setResource(KEY);
        // set limit qps to 20
        rule1.setCount(20);
        rule1.setGrade(RuleConstant.FLOW_GRADE_QPS);
        rule1.setLimitApp("default");
        rules.add(rule1);
        FlowRuleManager.loadRules(rules);
    }

For more details please refer to Flow control.

Circuit Break (DegradeRule)

Key fields:

Field	Description	Default value
resource	resource name
count	threshold
grade	by response time or exception ratio	response time
timeWindow	degrade time window

Multiple rules can be applied to the same resource.

API

API:DegradeRuleManager.loadRules() can be used to configure degradation rules.

 private static void initDegradeRule() {
        List<DegradeRule> rules = new ArrayList<DegradeRule>();
        DegradeRule rule = new DegradeRule();
        rule.setResource(KEY);
        // set threshold rt, 10 ms
        rule.setCount(10);
        rule.setGrade(RuleConstant.DEGRADE_GRADE_RT);
        rule.setTimeWindow(10);
        rules.add(rule);
        DegradeRuleManager.loadRules(rules);
    }

For more details, please refer to Circuit Break.

System protection rule (SystemRule)

Key factors

Field	Description	Default value
highestSystemLoad	threshold of Load1	-1(not valid)
avgRt	average response time	-1(not valid)
maxThread	concurrent thread count	-1(not valid)

API

API:SystemRuleManager.loadRules()

 private static void initDegradeRule() {
        List<SystemRule> rules = new ArrayList<SystemRule>();
        SystemRule rule = new SystemRule();
        rule.setHighestSystemLoad(10);
        rules.add(rule);
        DegradeRuleManager.loadRules(rules);
    }

For more details, please refer to System Protection.

HTTP Commands for Rules

You can also use HTTP commands to configure, query and update Sentinel rules.

To use these commands, make sure that the following library has been introduced:

<dependency>
    <groupId>com.alibaba.csp</groupId>
    <artifactId>sentinel-transport-simple-http</artifactId>
    <version>x.y.z</version>
</dependency>

Query command

curl http://localhost:8719/getRules?type=<XXXX>

• type=flow for flow rules;
• type=degrade for circuit breaking rules;
• type=system for system protection rules.

Rules will be returned in JSON format.

Modification command

curl http://localhost:8719/setRules?type=<XXXX>&data=<DATA>

Integrate with rule repositories

DataSource is designed to integrate rules to customized repositories and make rules persistent.

For more details, you can refer to Dynamic Rules.