物联网架构成长之路(55)-Gateway+Sentinel实现限流、熔断

0. 前言
　　之前有一篇博客讲到入门Sentinel，这次就将Sentinel引入到实际项目中进行演示。

1.启动Sentinel
　　具体可以参考这篇博客
　　https://www.cnblogs.com/wunaozai/p/12404712.html

java -jar sentinel-dashboadr-1.7.1.jar --server.port=8858

　　项目中pom.xml引入

        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba.csp</groupId>
            <artifactId>sentinel-datasource-nacos</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba.csp</groupId>
            <artifactId>sentinel-transport-simple-http</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba.csp</groupId>
            <artifactId>sentinel-spring-cloud-gateway-adapter</artifactId>
        </dependency>

　　以下配置追加到xxx-story-gateway-dev.properties的配置中，表示集成Sentinel

spring.cloud.sentinel.transport.dashboard=127.0.0.1:8858
spring.cloud.sentinel.datasource.ds.nacos.server-addr=127.0.0.1:8848
spring.cloud.sentinel.datasource.ds.nacos.data-id=gateway-sentinel.properties
spring.cloud.sentinel.datasource.ds.nacos.namespace=0e152861-1efa-62ea-9125-e569abc29691
spring.cloud.sentinel.datasource.ds.nacos.group-id=DEFAULT_GROUP
spring.cloud.sentinel.datasource.ds.nacos.data-type=json
spring.cloud.sentinel.datasource.ds.nacos.rule-type=flow

2. 动态修改Nacos上的Sentinel配置

[
    {
        "resource": "/hello",
        "limitApp": "default",
        "grade": 1,
        "count": 5,
        "strategy": 0,
        "controlBehavior": 0,
        "clusterMode": false
    },
    {
        "resource": "/aiml/v1/ai/chat",
        "limitApp": "default",
        "grade": 1,
        "count": 2,
        "strategy": 0,
        "controlBehavior": 0,
        "clusterMode": false
    }
]

3. 配置Sentinel Configuration
　　在对流量进行限流和熔断过程中，需要一些自定义操作。此时就需要增加一个GatewayConfiguration配置类。因为默认提示异常是【Blocked by Sentinel: FlowException】，所以最好是能，自定义异常提示。
　　GatewayConfiguration.java

package com.wunaozai.demo.story.gateway.config;

import java.util.Collections;
import java.util.List;

import org.springframework.beans.factory.ObjectProvider;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.http.codec.ServerCodecConfigurer;
import org.springframework.web.reactive.result.view.ViewResolver;

import com.alibaba.csp.sentinel.adapter.gateway.sc.SentinelGatewayFilter;

@Configuration
public class GatewayConfiguration {

    private final List<ViewResolver> views;
    private final ServerCodecConfigurer configurer;
    
    public GatewayConfiguration(ObjectProvider<List<ViewResolver>> views,
            ServerCodecConfigurer config) {
        this.views = views.getIfAvailable(Collections::emptyList);
        this.configurer = config;
    }
    
    /**
     * 配置SentinelGatewayBlockExceptionHandler，限流后异常处理
     * @return
     */
    @Bean
    @Order(Ordered.HIGHEST_PRECEDENCE)
    public JsonSentinelGatewayBlockExceptionHandler sentinelGatewayBlockExceptionHandler() {
        //return new SentinelGatewayBlockExceptionHandler(views, configurer);
        return new JsonSentinelGatewayBlockExceptionHandler(views, configurer);
    }
    
    /**
     * Sentinel 过滤器
     * @return
     */
    @Bean
    @Order(-1)
    public GlobalFilter sentinelGatewayFilter() {
        return new SentinelGatewayFilter();
    }
    
}

　　JsonSentinelGatewayBlockExceptionHandler.java

package com.wunaozai.demo.story.gateway.config;

import java.nio.charset.StandardCharsets;
import java.util.List;

import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.http.codec.HttpMessageWriter;
import org.springframework.http.codec.ServerCodecConfigurer;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.web.reactive.function.server.ServerResponse;
import org.springframework.web.reactive.result.view.ViewResolver;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebExceptionHandler;

import com.alibaba.csp.sentinel.adapter.gateway.sc.callback.GatewayCallbackManager;
import com.alibaba.csp.sentinel.slots.block.BlockException;
import com.alibaba.csp.sentinel.util.function.Supplier;

import reactor.core.publisher.Mono;

/**
 * Sentinel 限流后自定义异常
 * @author wunaozai
 * @Date 2020-03-17
 */
public class JsonSentinelGatewayBlockExceptionHandler implements WebExceptionHandler {

    private List<ViewResolver> viewResolvers;
    private List<HttpMessageWriter<?>> messageWriters;

    public JsonSentinelGatewayBlockExceptionHandler(
            List<ViewResolver> viewResolvers, ServerCodecConfigurer serverCodecConfigurer) {
        this.viewResolvers = viewResolvers;
        this.messageWriters = serverCodecConfigurer.getWriters();
    }
    /**
     * 自定义返回
     * @param response
     * @param exchange
     * @return
     */
    private Mono<Void> writeResponse(ServerResponse response, ServerWebExchange exchange) {
        ServerHttpResponse resp = exchange.getResponse();
        resp.getHeaders().add("Content-Type", "application/json;charset=UTF-8");
        String json = "{"code": -1, "data": null, "msg": "系统限流"}";
        DataBuffer buffer = resp.bufferFactory().wrap(json.getBytes(StandardCharsets.UTF_8));
        return resp.writeWith(Mono.just(buffer));
    }

    @Override
    public Mono<Void> handle(ServerWebExchange exchange, Throwable ex) {
        if (exchange.getResponse().isCommitted()) {
            return Mono.error(ex);
        }
        if (!BlockException.isBlockException(ex)) {
            return Mono.error(ex);
        }
        return handleBlockedRequest(exchange, ex)
            .flatMap(response -> writeResponse(response, exchange));
    }
    private Mono<ServerResponse> handleBlockedRequest(ServerWebExchange exchange, Throwable throwable) {
        return GatewayCallbackManager.getBlockHandler().handleRequest(exchange, throwable);
    }
    private final Supplier<ServerResponse.Context> contextSupplier = () -> new ServerResponse.Context() {
        @Override
        public List<HttpMessageWriter<?>> messageWriters() {
            return JsonSentinelGatewayBlockExceptionHandler.this.messageWriters;
        }
        @Override
        public List<ViewResolver> viewResolvers() {
            return JsonSentinelGatewayBlockExceptionHandler.this.viewResolvers;
        }
    };
}

4. 熔断机制
　　上面介绍的是限流，可以从 spring.cloud.sentinel.datasource.ds.nacos.rule-type=flow 看出来。但是根据 org.springframework.cloud.alibaba.sentinel.datasource.RuleType 这个枚举，Sentinel还提供了熔断机制。

　　修改之前的配置，增加多一个数据源，一个是限流，一个是熔断

#Sentinel
spring.cloud.sentinel.transport.dashboard=127.0.0.1:8858
spring.cloud.sentinel.datasource.ds1.nacos.server-addr=127.0.0.1:8848
spring.cloud.sentinel.datasource.ds1.nacos.data-id=gateway-sentinel.properties
spring.cloud.sentinel.datasource.ds1.nacos.namespace=0e152861-1efa-62ea-9125-e569abc29691
spring.cloud.sentinel.datasource.ds1.nacos.group-id=DEFAULT_GROUP
spring.cloud.sentinel.datasource.ds1.nacos.data-type=json
spring.cloud.sentinel.datasource.ds1.nacos.rule-type=flow

spring.cloud.sentinel.datasource.ds2.nacos.server-addr=127.0.0.1:8848
spring.cloud.sentinel.datasource.ds2.nacos.data-id=gateway-sentinel-degrade.properties
spring.cloud.sentinel.datasource.ds2.nacos.namespace=0e152861-1efa-62ea-9125-e569abc29691
spring.cloud.sentinel.datasource.ds2.nacos.group-id=DEFAULT_GROUP
spring.cloud.sentinel.datasource.ds2.nacos.data-type=json
spring.cloud.sentinel.datasource.ds2.nacos.rule-type=degrade

　　这个配置的意思是，如果请求xxx-story-res这个微服务是，当资源的平均响应时间超过阈值100ms后，资源进入准降级状态。如果接下来1秒内持续进入多个请求的RT时间都持续超过这个阈值，那么在接下来的时间窗口（timeWindow）30（秒）之内。对该方法的调用都会自动熔断。直接返回错误。这里会直接返回上面配置的 {"code": -1, "data": null, "msg": "系统限流"} 错误。

[
  {
    "resource": "xxx-story-res",
    "count": 100,
    "grade": 0,
    "timeWindow": 30
  }
]

　　现在测试，就是不断的请求对应的接口，从图中可以看到，每隔30秒，就会放一些请求到后面的服务。其他时间的请求，都是快速失败。返回限流。

5. 附录各个在Nacos上的配置 

参考资料：
　　https://github.com/alibaba/Sentinel/wiki/%E7%83%AD%E7%82%B9%E5%8F%82%E6%95%B0%E9%99%90%E6%B5%81
　　https://www.cnblogs.com/yinjihuan/p/10772558.html
　　https://www.cnblogs.com/zhangpan1244/p/11228020.html

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