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As distributed systems become increasingly popular, the reliability between services is becoming more important than ever before.Sentinel takes "flow" as breakthrough point, and works on multiple fields includingflow control,traffic shaping,circuit breaking andsystem adaptive protection, to guarantee reliability and resilience for microservices.

Sentinel has the following features:

• Rich applicable scenarios: Sentinel has been wildly used in Alibaba, and has covered almost all the core-scenarios in Double-11 (11.11) Shopping Festivals in the past 10 years, such as “Second Kill” which needs to limit burst flow traffic to meet the system capacity, message peak clipping and valley fills, circuit breaking for unreliable downstream services, cluster flow control, etc.
• Real-time monitoring: Sentinel also provides real-time monitoring ability. You can see the runtime information of a single machine in real-time, and the aggregated runtime info of a cluster with less than 500 nodes.
• Widespread open-source ecosystem: Sentinel provides out-of-box integrations with commonly-used frameworks and libraries such as Spring Cloud, Dubbo and gRPC. You can easily use Sentinel by simply add the adapter dependency to your services.
• Polyglot support: Sentinel has provided native support for Java,Go andC++.
• Various SPI extensions: Sentinel provides easy-to-use SPI extension interfaces that allow you to quickly customize your logic, for example, custom rule management, adapting data sources, and so on.

Features overview:

See theSentinel for the document website.

See the中文文档 for document in Chinese.

See theWiki for full documentation, examples, blog posts, operational details and other information.

Sentinel provides integration modules for various open-source frameworks(e.g. Spring Cloud, Apache Dubbo, gRPC, Spring WebFlux, Reactor) and service mesh.You can refer tothe document for more information.

If you are using Sentinel, pleaseleave a comment here to tell us your scenario to make Sentinel better.It's also encouraged to add the link of your blog post, tutorial, demo or customized components toAwesome Sentinel.

Below is a simple demo that guides new users to use Sentinel in just 3 steps. It also shows how to monitor this demo using the dashboard.

Note: Sentinel requires JDK 1.8 or later.

If you're using Maven, just add the following dependency inpom.xml.

<!-- replace here with the latest version--><dependency>    <groupId>com.alibaba.csp</groupId>    <artifactId>sentinel-core</artifactId>    <version>1.8.1</version></dependency>

If not, you can download JAR inMaven Center Repository.

Wrap your code snippet via Sentinel API:SphU.entry(resourceName).In below example, it isSystem.out.println("hello world");:

try (Entryentry =SphU.entry("HelloWorld")) {// Your business logic here.System.out.println("hello world");}catch (BlockExceptione) {// Handle rejected request.e.printStackTrace();}// try-with-resources auto exit

So far the code modification is done. We've also providedannotation support module to define resource easier.

If we want to limit the access times of the resource, we canset rules to the resource.The following code defines a rule that limits access to the resource to 20 times per second at the maximum.

List<FlowRule>rules =newArrayList<>();FlowRulerule =newFlowRule();rule.setResource("HelloWorld");// set limit qps to 20rule.setCount(20);rule.setGrade(RuleConstant.FLOW_GRADE_QPS);rules.add(rule);FlowRuleManager.loadRules(rules);

For more information, please refer toHow To Use.

After running the demo for a while, you can see the following records in~/logs/csp/${appName}-metrics.log.{date} (When using the defaultDateFileLogHandler).

|--timestamp-|------date time----|-resource-|p |block|s |e|rt  |occupied1529998904000|2018-06-26 15:41:44|HelloWorld|20|0    |20|0|0   |01529998905000|2018-06-26 15:41:45|HelloWorld|20|5579 |20|0|728 |01529998906000|2018-06-26 15:41:46|HelloWorld|20|15698|20|0|0   |01529998907000|2018-06-26 15:41:47|HelloWorld|20|19262|20|0|0   |01529998908000|2018-06-26 15:41:48|HelloWorld|20|19502|20|0|0   |01529998909000|2018-06-26 15:41:49|HelloWorld|20|18386|20|0|0   |0p stands for incoming request, block for blocked by rules, s for success handled by Sentinel, e for exception count, rt for average response time (ms), occupied stands for occupiedPassQps since 1.5.0 which enable us booking more than 1 shot when entering.

This shows that the demo can print "hello world" 20 times per second.

More examples and information can be found in theHow To Use section.

The working principles of Sentinel can be found inHow it works section.

Samples can be found in thesentinel-demo module.

Note: Java 8 is required for building or running the dashboard.

Sentinel also provides a simple dashboard application, on which you can monitor the clients and configure the rules in real time.

For details please refer toDashboard.

Sentinel will generate logs for troubleshooting and real-time monitoring.All the information can be found inlogs.

For bug report, questions and discussions please submitGitHub Issues.

Contact us viaGitter orEmail.

Contributions are always welcomed! Please refer toCONTRIBUTING for detailed guidelines.

You can start with the issues labeled withgood first issue.

ThanksGuava, which provides some inspiration on rate limiting.

And thanks for allcontributors of Sentinel!

These are only part of the companies using Sentinel, for reference only.If you are using Sentinel, pleaseadd your company here to tell us your scenario to make Sentinel better :)