Configuration 如何在envoyproxy中配置回退？

我正在尝试将特使配置为负载平衡器，目前遇到了回退。在我的游乐场集群中，我有3个后端服务器和特使作为前端代理。我正在通过围攻和观察反应生成一些关于特使的流量。这样做时，我停止了一个后端

我想要什么：特使应该将失败的请求从停止的后端重新发送到正常的后端，这样我就不会得到任何5xx响应

我得到了什么：当停止后端时，我得到了503个响应，然后一切又恢复正常

我做错了什么？我认为，

fallback\u policy

应该提供此功能，但它不起作用

这是我的配置文件：

node:
  id: LoadBalancer_01
  cluster: HighloadCluster
admin:
  access_log_path: /var/log/envoy/admin_access.log
  address:
    socket_address: { address: 0.0.0.0, port_value: 9901 }
static_resources:
  listeners:
    - name: http_listener
      address:
        socket_address: { address: 0.0.0.0, port_value: 80 }
      filter_chains:
        - filters:
            - name: envoy.http_connection_manager
              typed_config:
                "@type": type.googleapis.com/envoy.config.filter.network.http_connection_manager.v2.HttpConnectionManager
                stat_prefix: ingress_http
                codec_type: AUTO
                route_config:
                  name: request_route
                  virtual_hosts:
                    - name: local_service
                      domains: ["*"]
                      require_tls: NONE
                      routes:
                        - match: { prefix: "/" }
                          route:
                            cluster: backend_service
                            timeout: 1.5s
                          retry_policy:
                            retry_on: 5xx
                            num_retries: 3
                            per_try_timeout: 3s
                http_filters:
                  - name: envoy.router
                    typed_config:
                      "@type": type.googleapis.com/envoy.config.filter.http.router.v2.Router
                      name: envoy.file_access_log
                      typed_config:
                        "@type": type.googleapis.com/envoy.config.accesslog.v2.FileAccessLog
                        path: /var/log/envoy/access.log
  clusters:
    - name: backend_service
      connect_timeout: 0.25s
      type: STATIC
      lb_policy: ROUND_ROBIN
      lb_subset_config:
        fallback_policy: ANY_ENDPOINT
      outlier_detection:
        consecutive_5xx: 1
        interval: 10s
      load_assignment:
        cluster_name: backend_service
        endpoints:
          - lb_endpoints:
              - endpoint:
                  address:
                    socket_address:
                      address: 1.1.1.1
                      port_value: 10000
              - endpoint:
                  address:
                    socket_address:
                      address: 2.2.2.2
                      port_value: 10000
              - endpoint:
                  address:
                    socket_address:
                      address: 3.3.3.3
                      port_value: 10000
      health_checks:
          - http_health_check:
              path: /api/liveness-probe
            timeout: 1s
            interval: 30s
            unhealthy_interval: 10s
            unhealthy_threshold: 2
            healthy_threshold: 1
            always_log_health_check_failures: true
            event_log_path: /var/log/envoy/health_check.log```