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本文主要研究一下spring-cloud-kubernetes-client-loadbalancer

ServiceInstanceListSupplier

org/springframework/cloud/loadbalancer/core/ServiceInstanceListSupplier.java

public interface ServiceInstanceListSupplier extends Supplier<Flux<List<ServiceInstance>>> {

    String getServiceId();

    default Flux<List<ServiceInstance>> get(Request request) {
        return get();
    }

    static ServiceInstanceListSupplierBuilder builder() {
        return new ServiceInstanceListSupplierBuilder();
    }

}

spring-cloud-loadbalancer定义了ServiceInstanceListSupplier，它继承自Supplier，其泛型为Flux<List<ServiceInstance>>，它定义了getServiceId、get(Request)方法，并提供了builder静态方法

Request

org/springframework/cloud/client/loadbalancer/Request.java

public interface Request<C> {

    // Avoid breaking backward compatibility
    default C getContext() {
        return null;
    }

    // TODO: define contents

}

Request提供了getContext方法，默认返回null

DefaultRequest

org/springframework/cloud/client/loadbalancer/DefaultRequest.java

public class DefaultRequest<T> implements Request<T> {

    private T context;

    public DefaultRequest() {
        new DefaultRequestContext();
    }

    public DefaultRequest(T context) {
        this.context = context;
    }

    @Override
    public T getContext() {
        return context;
    }

    public void setContext(T context) {
        this.context = context;
    }

    @Override
    public String toString() {
        ToStringCreator to = new ToStringCreator(this);
        to.append("context", context);
        return to.toString();
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof DefaultRequest<?> that)) {
            return false;
        }
        return Objects.equals(context, that.context);
    }

    @Override
    public int hashCode() {
        return Objects.hash(context);
    }

}

DefaultRequest实现了Request，其定义的泛型为context的类型

ServiceInstanceListSupplier

spring-cloud-kubernetes-commons/src/main/java/org/springframework/cloud/kubernetes/commons/loadbalancer/KubernetesServicesListSupplier.java

public abstract class KubernetesServicesListSupplier implements ServiceInstanceListSupplier {

    protected final Environment environment;

    protected final KubernetesDiscoveryProperties discoveryProperties;

    protected final KubernetesServiceInstanceMapper mapper;

    public KubernetesServicesListSupplier(Environment environment, KubernetesServiceInstanceMapper mapper,
            KubernetesDiscoveryProperties discoveryProperties) {
        this.environment = environment;
        this.discoveryProperties = discoveryProperties;
        this.mapper = mapper;
    }

    @Override
    public String getServiceId() {
        return environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
    }

    @Override
    public abstract Flux<List<ServiceInstance>> get();

}

KubernetesServicesListSupplier声明实现ServiceInstanceListSupplier接口，它是一个抽象类，定义了get方法，这里忽略了get(Request)，没有将Request传递下来

KubernetesClientServicesListSupplier

spring-cloud-kubernetes-client-loadbalancer/src/main/java/org/springframework/cloud/kubernetes/client/loadbalancer/KubernetesClientServicesListSupplier.java

public class KubernetesClientServicesListSupplier extends KubernetesServicesListSupplier {

    private static final Log LOG = LogFactory.getLog(KubernetesClientServicesListSupplier.class);

    private CoreV1Api coreV1Api;

    private KubernetesClientProperties kubernetesClientProperties;

    private KubernetesNamespaceProvider kubernetesNamespaceProvider;

    public KubernetesClientServicesListSupplier(Environment environment, KubernetesServiceInstanceMapper mapper,
            KubernetesDiscoveryProperties discoveryProperties, CoreV1Api coreV1Api,
            KubernetesNamespaceProvider kubernetesNamespaceProvider) {
        super(environment, mapper, discoveryProperties);
        this.coreV1Api = coreV1Api;
        this.kubernetesNamespaceProvider = kubernetesNamespaceProvider;
    }

    private String getNamespace() {
        return kubernetesNamespaceProvider != null ? kubernetesNamespaceProvider.getNamespace()
                : kubernetesClientProperties.namespace();
    }

    @Override
    public Flux<List<ServiceInstance>> get() {
        LOG.info("Getting services with id " + this.getServiceId());
        List<ServiceInstance> result = new ArrayList<>();
        List<V1Service> services;
        try {
            if (discoveryProperties.allNamespaces()) {
                services = coreV1Api.listServiceForAllNamespaces(null, null, "metadata.name=" + this.getServiceId(),
                        null, null, null, null, null, null, null, null).getItems();
            }
            else {
                services = coreV1Api.listNamespacedService(getNamespace(), null, null, null,
                        "metadata.name=" + this.getServiceId(), null, null, null, null, null, null, null).getItems();
            }
            services.forEach(service -> result.add(mapper.map(service)));
        }
        catch (ApiException e) {
            LOG.warn("Error retrieving service with name " + this.getServiceId(), e);
        }
        LOG.info("Returning services: " + result);
        return Flux.defer(() -> Flux.just(result));
    }

}

KubernetesClientServicesListSupplier继承了KubernetesServicesListSupplier，其构造器依赖KubernetesServiceInstanceMapper、KubernetesDiscoveryProperties、CoreV1Api、KubernetesNamespaceProvider；其get方法使用coreV1Api.listServiceForAllNamespaces或者coreV1Api.listNamespacedService来返回指定serviceId的V1Service信息，之后通过mapper转换为ServiceInstance

V1Service

io/kubernetes/client/openapi/models/V1Service.java

public class V1Service implements io.kubernetes.client.common.KubernetesObject {
  public static final String SERIALIZED_NAME_API_VERSION = "apiVersion";
  @SerializedName(SERIALIZED_NAME_API_VERSION)
  private String apiVersion;

  public static final String SERIALIZED_NAME_KIND = "kind";
  @SerializedName(SERIALIZED_NAME_KIND)
  private String kind;

  public static final String SERIALIZED_NAME_METADATA = "metadata";
  @SerializedName(SERIALIZED_NAME_METADATA)
  private V1ObjectMeta metadata;

  public static final String SERIALIZED_NAME_SPEC = "spec";
  @SerializedName(SERIALIZED_NAME_SPEC)
  private V1ServiceSpec spec;

  public static final String SERIALIZED_NAME_STATUS = "status";
  @SerializedName(SERIALIZED_NAME_STATUS)
  private V1ServiceStatus status;

  //......
}  

V1Service定义了apiVersion、kind、metadata、spec、status属性

KubernetesServiceInstanceMapper

spring-cloud-kubernetes-commons/src/main/java/org/springframework/cloud/kubernetes/commons/loadbalancer/KubernetesServiceInstanceMapper.java

public interface KubernetesServiceInstanceMapper<T> {

    KubernetesServiceInstance map(T service);

    static String createHost(String serviceName, String namespace, String clusterDomain) {
        return String.format("%s.%s.svc.%s", serviceName, StringUtils.hasText(namespace) ? namespace : "default",
                clusterDomain);
    }

    static boolean isSecure(Map<String, String> labels, Map<String, String> annotations, String servicePortName,
            Integer servicePort) {
        if (labels != null) {
            final String securedLabelValue = labels.getOrDefault("secured", "false");
            if (securedLabelValue.equals("true")) {
                return true;
            }
        }

        if (annotations != null) {
            final String securedAnnotationValue = annotations.getOrDefault("secured", "false");
            if (securedAnnotationValue.equals("true")) {
                return true;
            }
        }
        return (servicePortName != null && servicePortName.endsWith("https")) || servicePort.toString().endsWith("443");
    }

    static Map<String, String> getMapWithPrefixedKeys(Map<String, String> map, String prefix) {
        if (map == null) {
            return new HashMap<>();
        }
        if (!StringUtils.hasText(prefix)) {
            return map;
        }
        final Map<String, String> result = new HashMap<>();
        map.forEach((k, v) -> result.put(prefix + k, v));
        return result;
    }

}

KubernetesServiceInstanceMapper接口定义了map方法，它提供了createHost、isSecure、getMapWithPrefixedKeys静态方法

KubernetesClientServiceInstanceMapper

spring-cloud-kubernetes-client-loadbalancer/src/main/java/org/springframework/cloud/kubernetes/client/loadbalancer/KubernetesClientServiceInstanceMapper.java

public class KubernetesClientServiceInstanceMapper implements KubernetesServiceInstanceMapper<V1Service> {

    private KubernetesLoadBalancerProperties properties;

    private KubernetesDiscoveryProperties discoveryProperties;

    public KubernetesClientServiceInstanceMapper(KubernetesLoadBalancerProperties properties,
            KubernetesDiscoveryProperties discoveryProperties) {
        this.properties = properties;
        this.discoveryProperties = discoveryProperties;
    }

    @Override
    public KubernetesServiceInstance map(V1Service service) {
        final V1ObjectMeta meta = service.getMetadata();

        final List<V1ServicePort> ports = service.getSpec().getPorts();
        V1ServicePort port = null;
        if (ports.size() == 1) {
            port = ports.get(0);
        }
        else if (ports.size() > 1 && StringUtils.hasText(this.properties.getPortName())) {
            Optional<V1ServicePort> optPort = ports.stream()
                    .filter(it -> properties.getPortName().endsWith(it.getName())).findAny();
            if (optPort.isPresent()) {
                port = optPort.get();
            }
        }
        if (port == null) {
            return null;
        }
        final String host = KubernetesServiceInstanceMapper.createHost(service.getMetadata().getName(),
                service.getMetadata().getNamespace(), properties.getClusterDomain());
        final boolean secure = KubernetesServiceInstanceMapper.isSecure(service.getMetadata().getLabels(),
                service.getMetadata().getAnnotations(), port.getName(), port.getPort());
        return new DefaultKubernetesServiceInstance(meta.getUid(), meta.getName(), host, port.getPort(),
                getServiceMetadata(service), secure);
    }

    private Map<String, String> getServiceMetadata(V1Service service) {
        final Map<String, String> serviceMetadata = new HashMap<>();
        KubernetesDiscoveryProperties.Metadata metadataProps = this.discoveryProperties.metadata();
        if (metadataProps.addLabels()) {
            Map<String, String> labelMetadata = KubernetesServiceInstanceMapper
                    .getMapWithPrefixedKeys(service.getMetadata().getLabels(), metadataProps.labelsPrefix());
            serviceMetadata.putAll(labelMetadata);
        }
        if (metadataProps.addAnnotations()) {
            Map<String, String> annotationMetadata = KubernetesServiceInstanceMapper
                    .getMapWithPrefixedKeys(service.getMetadata().getAnnotations(), metadataProps.annotationsPrefix());
            serviceMetadata.putAll(annotationMetadata);
        }

        return serviceMetadata;
    }

}

KubernetesClientServiceInstanceMapper实现了KubernetesServiceInstanceMapper接口，其泛型为V1Service，其map方法先通过service.getSpec().getPorts()获取port信息，之后通过createHost返回svc的短域名<servicename>.<namespace>.svc.<clusterdomain>，例如service-a.default.svc.cluster.local，最后创建DefaultKubernetesServiceInstance

KubernetesClientLoadBalancerClientConfiguration

spring-cloud-kubernetes-client-loadbalancer/src/main/java/org/springframework/cloud/kubernetes/client/loadbalancer/KubernetesClientLoadBalancerClientConfiguration.java

public class KubernetesClientLoadBalancerClientConfiguration {

    @Bean
    @ConditionalOnProperty(name = "spring.cloud.kubernetes.loadbalancer.mode", havingValue = "SERVICE")
    ServiceInstanceListSupplier kubernetesServicesListSupplier(Environment environment, CoreV1Api coreV1Api,
            KubernetesClientServiceInstanceMapper mapper, KubernetesDiscoveryProperties discoveryProperties,
            KubernetesNamespaceProvider kubernetesNamespaceProvider, ConfigurableApplicationContext context) {
        return ServiceInstanceListSupplier.builder().withBase(new KubernetesClientServicesListSupplier(environment,
                mapper, discoveryProperties, coreV1Api, kubernetesNamespaceProvider)).withCaching().build(context);
    }

}

KubernetesClientLoadBalancerClientConfiguration在spring.cloud.kubernetes.loadbalancer.mode设置为SERVICE的时候会自动创建kubernetesServicesListSupplier

小结

spring-cloud-loadbalancer定义了ServiceInstanceListSupplier，它继承自Supplier，其泛型为Flux<List<ServiceInstance>>，它定义了getServiceId、get(Request)方法，并提供了builder静态方法；KubernetesServicesListSupplier声明实现ServiceInstanceListSupplier接口，它是一个抽象类，定义了get方法；KubernetesClientServicesListSupplier继承了KubernetesServicesListSupplier，其构造器依赖KubernetesServiceInstanceMapper、KubernetesDiscoveryProperties、CoreV1Api、KubernetesNamespaceProvider；其get方法使用coreV1Api.listServiceForAllNamespaces或者coreV1Api.listNamespacedService来返回指定serviceId的V1Service信息，之后通过mapper转换为ServiceInstance。

整体来看spring-cloud-kubernetes-client-loadbalancer目前仅支持spring.cloud.kubernetes.loadbalancer.mode为SERVICE的模式，其实内部还是走的k8s的service的域名解析及负载均衡，无法细粒度到个性化的负载均衡。