如何使用负载均衡算法

// Dubbo 3.3 RandomLoadBalance 核心逻辑（简化）
// dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/loadbalance/RandomLoadBalance.java
protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation invocation) {
    int length = invokers.size();
    boolean sameWeight = true;
    int[] weights = new int[length];
    int totalWeight = 0;
    // 计算总权重
    for (int i = 0; i < length; i++) {
        int weight = getWeight(invokers.get(i), invocation);
        weights[i] = weight;
        totalWeight += weight;
        if (sameWeight && i > 0 && weight != weights[i - 1]) {
            sameWeight = false;
        }
    }
    if (totalWeight > 0 && !sameWeight) {
        // 加权随机：在 [0, totalWeight) 区间内选一个随机偏移量
        int offset = ThreadLocalRandom.current().nextInt(totalWeight);
        for (int i = 0; i < length; i++) {
            offset -= weights[i];
            if (offset < 0) {
                return invokers.get(i);
            }
        }
    }
    return invokers.get(ThreadLocalRandom.current().nextInt(length));
}

// Dubbo 3.3 Smooth Weighted Round Robin 核心逻辑（简化）
// 关键：每次选择后动态调整 currentWeight，保证分布均匀
// 节点 A(3), B(2), C(1) 的选择序列为 A-A-B-A-C-B，而非 A-A-A-B-B-C

# Envoy Least Request LB 配置（Envoy 1.30+）
# weight = load_balancing_weight / (active_requests + 1)^active_request_bias
cluster:
  name: my_service
  type: EDS
  lb_policy: LEAST_REQUEST
  least_request_lb_config:
    choice_count: 2              # P2C：随机选 2 个候选
    active_request_bias: 1.0     # 活跃请求对权重的衰减系数

// Dubbo 3.3 自适应负载均衡核心思路（简化）
// 指标采集：RT（响应时间）、成功率、并发数
// 权重计算：dynamicWeight = staticWeight * (1 - errorRate) * (baselineRT / actualRT)
// 按动态权重排序，对底部 20% 节点降权

EWMA(t) = alpha * sample(t) + (1 - alpha) * EWMA(t-1)

# Envoy Maglev LB 配置（Envoy 1.30+）
cluster:
  name: redis_cluster
  lb_policy: MAGLEV
  maglev_lb_config:
    table_size: 65537    # 必须为质数，默认 65537

// Dubbo 3.3 自适应负载均衡配置
// application.yml
dubbo:
  consumer:
    loadbalance: adaptive
  provider:
    loadbalance: adaptive

// Spring Cloud LoadBalancer 配置（Spring Cloud 2023.x+）
@Configuration
public class LoadBalancerConfig {
    @Bean
    ReactorLoadBalancer<ServiceInstance> randomLoadBalancer(
            Environment environment,
            LoadBalancerClientFactory factory) {
        String name = environment.getProperty(
            LoadBalancerClientFactory.PROPERTY_NAME);
        return new RandomLoadBalancer(
            factory.getLazyProvider(name, ServiceInstanceListSupplier.class),
            name);
    }
}

// 支持的内置策略：Random、RoundRobin
// 可通过 ServiceInstanceListSupplier 自定义实例过滤和缓存

// gRPC xDS LB 配置（gRPC 1.62+）
// 优点：无需 Sidecar，客户端直接从控制面获取后端列表和负载均衡策略
// 支持：RoundRobin、RingHash、LeastRequest

# Istio 1.22+ DestinationRule 负载均衡配置
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: reviews
spec:
  host: reviews.prod.svc.cluster.local
  trafficPolicy:
    loadBalancer:
      simple: LEAST_REQUEST    # 支持：ROUND_ROBIN, LEAST_REQUEST, RANDOM, PASSTHROUGH
  subsets:
  - name: v2
    labels:
      version: v2
    trafficPolicy:
      loadBalancer:
        consistentHash:         # 一致性哈希配置
          httpHeaderName: "x-session-id"
          # 或使用 Cookie：
          # httpCookie:
          #   name: "session"
          #   ttl: 3600s
          # 或使用 Maglev：
          # 的 maglev 配置需要通过 EnvoyFilter 注入

# Istio 1.22+ Locality-Aware LB + Failover 配置
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: reviews-global
spec:
  host: reviews.prod.svc.cluster.local
  trafficPolicy:
    connectionPool:
      http:
        h2UpgradePolicy: UPGRADE
    outlierDetection:
      consecutive5xxErrors: 3
      interval: 30s
      baseEjectionTime: 30s
    loadBalancer:
      localityLbSetting:        # 地域感知配置
        enabled: true
        distribute:             # 自定义流量分布
        - from: us-west1/zone1/*
          to:
            "us-west1/zone1": 80    # 80% 流量留在本 Zone
            "us-west1/zone2": 20    # 20% 跨 Zone
        failover:               # 故障转移策略
        - from: us-west1
          to: us-east1
        - from: us-east1
          to: us-west1
      simple: LEAST_REQUEST

# Envoy 1.30+ ClientSideWeightedRoundRobin 配置
# 权重来源：上游通过 ORCA 报告 QPS、EPS、利用率
load_balancing_policy:
  policies:
  - typed_extension_config:
      name: envoy.load_balancing_policies.wrr_locality
      typed_config:
        "@type": type.googleapis.com/envoy.extensions.load_balancing_policies.wrr_locality.v3.WrrLocality
        endpoint_picking_policy:
          typed_extension_config:
            name: envoy.load_balancing_policies.client_side_weighted_round_robin
            typed_config:
              "@type": >-
                type.googleapis.com/envoy.extensions.load_balancing_policies.client_side_weighted_round_robin.v3.ClientSideWeightedRoundRobin
              slow_start_window: 600s   # 新节点慢启动窗口

# Cilium 1.16+ 安装（替换 kube-proxy）
# kubeadm init --skip-phases=addon/kube-proxy
helm install cilium cilium/cilium \
  --namespace kube-system \
  --set kubeProxyReplacement=true \
  --set k8sServiceHost=API_SERVER_IP \
  --set k8sServicePort=6443 \
  --set loadBalancer.algorithm=maglev   # 使用 Maglev 一致性哈希

# Istio 多集群 Locality Failover
# 当 us-west 集群不可用时，自动 failover 到 us-east
apiVersion: networking.istio.io/v1
kind: DestinationRule
metadata:
  name: reviews-multi-cluster
spec:
  host: reviews.prod.svc.cluster.local
  trafficPolicy:
    loadBalancer:
      localityLbSetting:
        enabled: true
        failover:
        - from: us-west1
          to: us-east1
      simple: LEAST_REQUEST
    outlierDetection:
      consecutive5xxErrors: 3
      interval: 30s
      baseEjectionTime: 30s