Spring Cloud升级之路 - Hoxton - 7. 后续更新（WebFlux等）

1. 修正实例列表乱序导致的负载均衡重试相同实例的问题

虽然之前考虑了通过每个请求的traceId隔离负载均衡的position来实现重试不会重试相同实例的问题，但是没有考虑在负载均衡过程中，实例列表的更新。

例如：

请求第一次调用负载均衡，实例列表是：[实例1，实例2]，position为1，对2取余=1，所以请求发送到实例2上面了
请求失败，触发重试，实例列表缓存失效，更新后变成了：[实例2，实例1]，position为2，对2取余=0，所以请求又发送到实例2上面了

private Response<ServiceInstance> getInstanceResponse(List<ServiceInstance> serviceInstances) {
    if (serviceInstances.isEmpty()) {
        log.warn("No servers available for service: " + this.serviceId);
        return new EmptyResponse();
    }
    Span currentSpan = tracer.currentSpan();
    //如果没有 traceId，就生成一个新的，但是最好检查下为啥会没有
    //是不是 MQ 消费这种没有主动生成 traceId 的情况，最好主动生成下
    if (currentSpan == null) {
        currentSpan = tracer.newTrace();
    }
    long l = currentSpan.context().traceId();
    int seed = positionCache.get(l).getAndIncrement();
    //这里，serviceInstances可能与上次的内容不同
    //例如上次是实例1，实例2
    //这次是实例2，实例1
    return new DefaultResponse(serviceInstances.get(seed % serviceInstances.size()));
}

所以，在这里追加排序，保证实例有序，从而进一步不会重试相同的实例。

private Response<ServiceInstance> getInstanceResponse(List<ServiceInstance> serviceInstances) {
    if (serviceInstances.isEmpty()) {
        log.warn("No servers available for service: " + this.serviceId);
        return new EmptyResponse();
    }
    Span currentSpan = tracer.currentSpan();
    //如果没有 traceId，就生成一个新的，但是最好检查下为啥会没有
    //是不是 MQ 消费这种没有主动生成 traceId 的情况，最好主动生成下
    if (currentSpan == null) {
        currentSpan = tracer.newTrace();
    }
    long l = currentSpan.context().traceId();
    int seed = positionCache.get(l).getAndIncrement();
    return new DefaultResponse(serviceInstances.stream().sorted(Comparator.comparing(ServiceInstance::getInstanceId)).collect(Collectors.toList()).get(seed % serviceInstances.size()));
}

2. WebFlux环境兼容与WebClient实现相同功能

maven依赖：

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.7.RELEASE</version>
    </parent>

    <properties>
        <disruptor.version>3.4.2</disruptor.version>
        <resilience4j-spring-cloud2.version>1.1.0</resilience4j-spring-cloud2.version>
    </properties>

    <dependencies>
        <!--内部缓存框架统一采用caffeine-->
        <!--这样Spring cloud loadbalancer用的本地实例缓存也是基于Caffeine-->
        <dependency>
            <groupId>com.github.ben-manes.caffeine</groupId>
            <artifactId>caffeine</artifactId>
        </dependency>

        <!--日志需要用log4j2-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-log4j2</artifactId>
        </dependency>

        <!--lombok简化代码-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>

        <!--注册到eureka-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>

        <!--spring cloud rpc相关-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <!--调用路径记录-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-sleuth</artifactId>
        </dependency>
        <!--暴露actuator相关端口-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-circuitbreaker-reactor-resilience4j</artifactId>
        </dependency>
        <dependency>
            <groupId>io.github.resilience4j</groupId>
            <artifactId>resilience4j-spring-cloud2</artifactId>
            <version>${resilience4j-spring-cloud2.version}</version>
        </dependency>
        <!--log4j2异步日志需要的依赖，所有项目都必须用log4j2和异步日志配置-->
        <dependency>
            <groupId>com.lmax</groupId>
            <artifactId>disruptor</artifactId>
            <version>${disruptor.version}</version>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Hoxton.SR4</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

其他的配置是一样的，重点在于，如何使用WebClient调用其他微服务，并且实现针对Get请求重试或者是所有请求的网络 IO 异常，例如connect timeout等等，或者是断路器异常（因为请求还没发出）。

WebClient可以加入各种Filter，通过实现这些Filter来实现实例级别的断路器还有重试。

源码：WebClientConfig.java

实现重试：

private static class RetryFilter implements ExchangeFilterFunction {
    private final String serviceName;

    private RetryFilter(String serviceName) {
        this.serviceName = serviceName;
    }

    @Override
    public Mono<ClientResponse> filter(ClientRequest clientRequest, ExchangeFunction exchangeFunction) {
        return exchangeFunction.exchange(clientRequest).retryWhen(Retry.onlyIf(retryContext -> {
            //get请求一定重试
            return clientRequest.method().equals(HttpMethod.GET)
                    //connect Timeout 是一种 IOException
                    || retryContext.exception() instanceof IOException
                    //实例级别的断路器的Exception
                    || retryContext.exception() instanceof CallNotPermittedException;
        }).retryMax(1).exponentialBackoff(Duration.ofMillis(100), Duration.ofMillis(1000)));
    }
}

实例级别的断路器：

private static class InstanceCircuitBreakerFilter implements ExchangeFilterFunction {
    private final String serviceName;
    private final CircuitBreakerRegistry circuitBreakerRegistry;
    ;

    private InstanceCircuitBreakerFilter(String serviceName, CircuitBreakerRegistry circuitBreakerRegistry) {
        this.serviceName = serviceName;
        this.circuitBreakerRegistry = circuitBreakerRegistry;
    }

    @Override
    public Mono<ClientResponse> filter(ClientRequest clientRequest, ExchangeFunction exchangeFunction) {
        CircuitBreaker circuitBreaker;
        //这时候的url是经过负载均衡器的，是实例的url
        String instancId = clientRequest.url().getHost() + ":" + clientRequest.url().getPort();
        try {
            //使用实例id新建或者获取现有的CircuitBreaker,使用serviceName获取配置
            circuitBreaker = circuitBreakerRegistry.circuitBreaker(instancId, serviceName);
        } catch (ConfigurationNotFoundException e) {
            circuitBreaker = circuitBreakerRegistry.circuitBreaker(instancId);
        }

        return exchangeFunction.exchange(clientRequest).transform(CircuitBreakerOperator.of(circuitBreaker));
    }
}

组装调用某个微服务(这里是service-provider)的WebClient：

public static final String SERVICE_PROVIDER = "service-provider";

@Autowired
private ReactorLoadBalancerExchangeFilterFunction lbFunction;

@Bean(SERVICE_PROVIDER)
public WebClient getWebClient(CircuitBreakerRegistry circuitBreakerRegistry) {
    ConnectionProvider provider = ConnectionProvider.builder(SERVICE_PROVIDER)
            .maxConnections(50).pendingAcquireTimeout(Duration.ofSeconds(5)).build();
    HttpClient httpClient = HttpClient.create(provider)
            .tcpConfiguration(client ->
                    //链接超时
                    client.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 500)
                            .doOnConnected(conn -> conn
                                    //读取超时
                                    .addHandlerLast(new ReadTimeoutHandler(1))
                                    .addHandlerLast(new WriteTimeoutHandler(1))
                            )
            );

    return WebClient.builder()
            .clientConnector(new ReactorClientHttpConnector(httpClient))
            //Retry在负载均衡前
            .filter(new RetryFilter(SERVICE_PROVIDER))
            //负载均衡器，改写url
            .filter(lbFunction)
            //实例级别的断路器需要在负载均衡获取真正地址之后
            .filter(new InstanceCircuitBreakerFilter(SERVICE_PROVIDER, circuitBreakerRegistry))
            .baseUrl("http://" + SERVICE_PROVIDER)
            .build();
}

这样，我们就可以实现和之前feign一样的微服务调用了。

@Log4j2
@RestController
public class TestController {
    @Resource(name = WebClientConfig.SERVICE_PROVIDER)
    private WebClient webClient;

    @RequestMapping("/testGetTimeOut")
    public Mono<String> testGetTimeOut() {
        return webClient.get().uri("/test-read-time-out")
                .retrieve()
                .bodyToMono(new ParameterizedTypeReference<>() {
                });
    }

    @RequestMapping("/testPostTimeOut")
    public Mono<String> testPostTimeOut() {
        return webClient.post().uri("/test-read-time-out")
                .retrieve()
                .bodyToMono(new ParameterizedTypeReference<>() {
                });
    }
}

Spring Cloud升级之路 - Hoxton - 7. 后续更新（WebFlux等）

1. 修正实例列表乱序导致的负载均衡重试相同实例的问题

2. WebFlux环境兼容与WebClient实现相同功能

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