Envoy 集群管理 位置加权负载均衡

组权重，基于locality划分的权重。

如果A组的健康端点比例为80%，B组的健康比例为60%，则按如下比例重新分配

A组权重 x 0.8 ：B组权重 x 0.6，同样此种方法为了避免一有变动就重新分配流量所以也支持超配因子。如果乘以超配因子的结果大于1则取1，小于1则取小于1的值。则组权重 x 健康比例 x 超配因子。

A:effective_weight= 8 x min(1, (1.4 x 0.8))

启用位置加权：

cluster:
- name: ...
  ...
  common_lb_config:
    locality_weighted_lb_config: {} # 启用位置加权负载均衡机制， 它没有可用的子参数；
    ...
  load_assignment:
    endpoints:
      locality: "{...}"
      lb_endpoints": []
      load_balancing_weight: "{}" # 整数值， 定义当前位置或优先级的权重， 最小值为1；
      priority: "..."

位置加权负载均衡与区域感知负载均衡互斥，与优先级负载均衡可共存。

先选择优先级

再在优先级相同的中按位置权重来分配。

如果相同优先级乘以超配因子健康端点小于百分之百则一部分流量分配到次一级的上来。

三级调度：

优先级调度 -> 位置加权负载均衡调度 -> 同一个组内的端点之间负载均衡算法调度

区域->组->端点

示例：

admin:
  access_log_path: "/dev/null"
  address:
    socket_address:
      address: 0.0.0.0
      port_value: 9901

static_resources:
  listeners:
  - address:
      socket_address:
        address: 0.0.0.0
        port_value: 80
    name: listener_http
    filter_chains:
    - filters:
      - name: envoy.http_connection_manager
        typed_config:
          "@type": type.googleapis.com/envoy.config.filter.network.http_connection_manager.v2.HttpConnectionManager
          codec_type: AUTO
          stat_prefix: ingress_http
          route_config:
            name: local_route
            virtual_hosts:
            - name: backend
              domains: 
              - "*"
              routes:
              - match:
                  prefix: "/"
                route:
                  cluster: webcluster1
          http_filters:
          - name: envoy.router

  clusters:
  - name: webcluster1
    connect_timeout: 0.25s
    type: STRICT_DNS
    lb_policy: ROUND_ROBIN
    http2_protocol_options: {}
    common_lb_config:
      locality_weighted_lb_config: {}
    load_assignment:
      cluster_name: webcluster1
      policy:
        overprovisioning_factor: 140
      endpoints:
      - locality:
          region: cn-north-1
        priority: 0
        load_balancing_weight: 10
        lb_endpoints:
        - endpoint:
            address:
              socket_address:
                address: colored
                port_value: 80
      - locality:
          region: cn-north-2
        priority: 0
        load_balancing_weight: 20
        lb_endpoints:
        - endpoint:
            address:
              socket_address:
                address: myservice
                port_value: 80
    health_checks:
    - timeout: 5s
      interval: 10s
      unhealthy_threshold: 2
      healthy_threshold: 1
      http_health_check:
        path: /healthz
        expected_status: 200