Guideline:Migration from Hystrix to Sentinel

As microservices become more popular, the stability between services becomes more and more important. Technologies such as flow control, fault tolerance, and system load protection are widely used in microservice systems to improve the robustness of the system and guarantee the stability of the business, and to minimize system outages caused by excessive access traffic and heavy system load.

Hystrix, an open source latency and fault tolerance library of Netflix, has recently announced on its GitHub homepage that new features are no longer under development. It is recommended that developers use other open source projects that are still active.So what are the alternatives?

Last time, we introduced two alternatives in the article, “Resilience4j and Sentinel: Two Open-Source Alternatives to Netflix Hystrix

This article will help you migrate from Hystrix to Sentinel and help you get up to speed on using Sentinel.

Feature in HystrixMigration SolutionFeature in SentinelThread Pool Isolation / Semaphore IsolationSentinel does not support thread pool isolation; In Sentinel, flow control in thread count mode represents semaphore isolation. If you are using semaphore isolation, you can simply add flow rules for target resource.Thread Count Flow ControlCircuit BreakerSentinel supports circuit breaking by average response time, exception ratio and exception count. If you want to use circuit breaking in Sentinel, you cam simply configure degrade rules for target resource.Circuit breaking with various strategyCommand DefinitionYou can define your resource entry (similar to command key) via SphU API in Sentinel. Resource definition and rule configuration are separate.Resource Entry DefinitionCommand ConfigurationRules can be hardcoded through the xxxRuleManager API in Sentinel, and multiple dynamic rule data sources are also supported.Rule ConfigurationHystrixCommand annotationSentinel also provides annotation support (SentinelResource), which is easy to use.SentinelResource annotationSpring Cloud NetflixSentinel provides out-of-box integration modules for Servlet, Dubbo, Spring Cloud, and gRPC. If you were using Spring Cloud Netflix previously, it's east for you to migrate to Spring Cloud Alibaba.Spring Cloud Alibaba

HystrixCommand

public class SomeCommand extends HystrixCommand<String> {    public SomeCommand() {
super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("SomeGroup"))
// command key
.andCommandKey(HystrixCommandKey.Factory.asKey("SomeCommand"))
// command configuration
.andCommandPropertiesDefaults(HystrixCommandProperties.Setter()
.withFallbackEnabled(true)
));
}
@Override
protected String run() {
// business logic
return "Hello World!";
}
}
// The execution model of Hystrix
// sync mode:
String s = new SomeCommand().execute();
// async mode (managed by Hystrix):
Observable<String> s = new SomeCommand().observe();

Sentinel does not specify an execution model, nor does it care how the code is executed. In Sentinel, what you should do is just to wrap your code with Sentinel API to define resources:

Entry entry = null;
try {
entry = SphU.entry("resourceName");
// your business logic here
return doSomeThing();
} catch (BlockException ex) {
// handle rejected
} finally {
if (entry != null) {
entry.exit();
}
}

In Hystrix, you usually have to configure rules when the command is defined. In Sentinel, resource definitions and rule configurations are separate. Users first define resources for the corresponding business logic through the Sentinel API, and then configure the rules when needed. For details, please refer to this document.

Thread Pool Isolation

Semaphore Isolation

public class CommandUsingSemaphoreIsolation extends HystrixCommand<String> {    private final int id;    public CommandUsingSemaphoreIsolation(int id) {
super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("SomeGroup"))
.andCommandPropertiesDefaults(HystrixCommandProperties.Setter()
.withExecutionIsolationStrategy(ExecutionIsolationStrategy.SEMAPHORE)
.withExecutionIsolationSemaphoreMaxConcurrentRequests(8)));
this.id = id;
}
@Override
protected String run() {
return "result_" + id;
}
}

In Sentinel, semaphore isolation is provided as a mode of flow control (thread count mode), so you only need to configure the flow rule for the resource:

FlowRule rule = new FlowRule("doSomething") // resource name
.setGrade(RuleConstant.FLOW_GRADE_THREAD) // thread count mode
.setCount(8); // max concurrency
FlowRuleManager.loadRules(Collections.singletonList(rule)); // load the rules

If you are using Sentinel dashboard, you can also easily configure the rules in dashboard.

Circuit Breaking

  1. circuitBreaker.errorThresholdPercentage: the threshold
  2. circuitBreaker.sleepWindowInMilliseconds: the sleep window when circuit breaker is open

For example:

public class FooServiceCommand extends HystrixCommand<String> {    protected FooServiceCommand(HystrixCommandGroupKey group) {
super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("OtherGroup"))
// command key
.andCommandKey(HystrixCommandKey.Factory.asKey("fooService"))
.andCommandPropertiesDefaults(HystrixCommandProperties.Setter()
.withExecutionTimeoutInMilliseconds(500)
.withCircuitBreakerRequestVolumeThreshold(5)
.withCircuitBreakerErrorThresholdPercentage(50)
.withCircuitBreakerSleepWindowInMilliseconds(10000)
));
}
@Override
protected String run() throws Exception {
return "some_result";
}
}

In Sentinel, you only need to configure circuit breaking rules for resources that want to be automatically degraded. For example, the rules corresponding to the Hystrix example above:

DegradeRule rule = new DegradeRule("fooService")
.setGrade(RuleConstant.DEGRADE_GRADE_EXCEPTION_RATIO) // exception ratio mode
.setCount(0.5) // ratio threshold (0.5 -> 50%)
.setTimeWindow(10); // sleep window (10s)
// load the rules
DegradeRuleManager.loadRules(Collections.singletonList(rule));

If you are using Sentinel dashboard, you can also easily configure the circuit breaking rules in dashboard.

In addition to the exception ratio mode, Sentinel also supports automatic circuit breaking based on average response time and minute exceptions.

Annotation Support

// original method
@HystrixCommand(fallbackMethod = "fallbackForGetUser")
User getUserById(String id) {
throw new RuntimeException("getUserById command failed");
}
// fallback method
User fallbackForGetUser(String id) {
return new User("admin");
}

Hystrix rule configuration is bundled with command execution. We can configure rules for command in the commandProperties property of the @HystrixCommand annotation, such as:

@HystrixCommand(commandProperties = {
@HystrixProperty(name = "circuitBreaker.errorThresholdPercentage", value = "50")
})
public User getUserById(String id) {
return userResource.getUserById(id);
}

Using Sentinel annotations is similar to Hystrix, as follows:

  1. Add the annotation support dependency: sentinel-annotation-aspectj and register the aspect as a Spring bean (if you are using Spring Cloud Alibaba then the bean will be injected automatically);
  2. Add the @SentinelResource annotation to the method that needs flow control and circuit breaking. You can set fallback or blockHandler functions in the annotation;
  3. Configure rules

For the details, you can refer to the annotation support document. An example for Sentinel annotation:

// original method
@SentinelResource(fallback = "fallbackForGetUser")
User getUserById(String id) {
throw new RuntimeException("getUserById command failed");
}
// fallback method (only invoked when the original resource triggers circuit breaking); If we need to handle for flow control / system protection, we can set `blockHandler` method
User fallbackForGetUser(String id) {
return new User("admin");
}

Then configure the rules:

  1. via API (e.g. DegradeRuleManager.loadRules(rules) method)
  • DegradeRule rule = new DegradeRule("getUserById") .setGrade(RuleConstant.DEGRADE_GRADE_EXCEPTION_RATIO) // exception ratio mode .setCount(0.5) // ratio threshold (0.5 -> 50%) .setTimeWindow(10); // sleep window (10s) // load the rules DegradeRuleManager.loadRules(Collections.singletonList(rule));
  1. via Sentinel dashboard

Integrations

Dynamic Configuration

Reference:https://www.alibabacloud.com/blog/guidelinemigration-from-hystrix-to-sentinel_594380?spm=a2c41.12516911.0.0

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