Getting Started with Alibaba Sentinel for Flow Control and Circuit Breaking in Spring Boot

Sentinel is an open‑source flow‑control and circuit‑breaker framework from Alibaba that provides a visual console for managing traffic, protecting service stability in microservice architectures.

Key features include rich application scenarios (e.g., flash‑sale traffic spikes, message peak‑valley smoothing), real‑time monitoring of single‑machine and cluster metrics, extensive integration with Spring Cloud, Dubbo, gRPC, and a complete set of SPI extension points for custom rule management.

Start the Sentinel dashboard : download the release JAR from the GitHub releases page and run it with java -jar sentinel-dashboard-1.6.0.jar. The dashboard will listen on port 8080 (or a custom port) and can be accessed at http://localhost:8080.

Client setup – create a Spring Boot project and add the following Maven pom.xml (excerpt):

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.5.RELEASE</version>
        <relativePath/>
    </parent>
    <groupId>com.maimeng.baobanq</groupId>
    <artifactId>baobanserver</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Finchley.SR1</spring-cloud.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- sentinel -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
        </dependency>
        <!-- sentinel end -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-alibaba-dependencies</artifactId>
                <version>0.2.2.RELEASE</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

Configuration : add the Sentinel server address to application.yml:

spring:
  application:
    name: baobanserver
  cloud:
    sentinel:
      transport:
        dashboard: localhost:8080
      #eager: true   # uncomment to disable lazy loading

Define a simple REST controller:

@RestController
public class TestController {
    @GetMapping(value = "/hello")
    public String hello() {
        return "Hello Sentinel";
    }
}

Run the Spring Boot application, then access the dashboard. Initially the service list is empty because no request has been made. Invoke /hello once; the dashboard will register the service. Set a flow‑control rule for the /hello endpoint with a threshold of 1 request per second. Subsequent rapid calls will be blocked, demonstrating Sentinel’s rate‑limiting in action.

Note: Sentinel uses lazy loading by default; the rule takes effect only after the first request. To enable eager loading, remove the comment on the eager property in application.yml.

By following these steps you have a functional Sentinel integration that provides real‑time monitoring, circuit breaking, and flow control for a Spring Boot microservice.