Istio中的流量配置

2024-01-02 22:45:04

Istio中的流量配置

Istio中的流量配置

Istio注入的容器

Istio的数据面会在pod中注入两个容器：istio-init和istio-proxy。

Istio-init

istio-init会通过创建iptables规则来接管流量：

命令行参数 -p 15001表示出向流量被iptable重定向到Envoy的15001端口
命令行参数 -z 15006表示入向流量被iptable重定向到Envoy的15006端口
命令行参数 -u 1337参数用于排除用户ID为1337，即Envoy自身的流量，以避免Iptable把Envoy发出的数据又重定向到Envoy，形成死循环。在istio-proxy容器中执行如下命令可以看到Envoy使用的用户id为1337。
```
$ id
uid=1337(istio-proxy) gid=1337(istio-proxy) groups=1337(istio-proxy)
```

  istio-iptables
  -p
  15001
  -z
  15006
  -u
  1337
  -m
  REDIRECT
  -i
  *
  -x

  -b
  *
  -d
  15090,15021,15020
  --run-validation
  --skip-rule-apply

istio-proxy

istio-proxy容器中会运行两个程序：pilot-agent和envoy。

$ ps -ef|cat
UID          PID    PPID  C STIME TTY          TIME CMD
istio-p+       1       0  0 Sep10 ?        00:03:39 /usr/local/bin/pilot-agent proxy sidecar --domain default.svc.cluster.local --serviceCluster sleep.default --proxyLogLevel=warning --proxyComponentLogLevel=misc:error --trust-domain=cluster.local --concurrency 2
istio-p+      27       1  0 Sep10 ?        00:14:30 /usr/local/bin/envoy -c etc/istio/proxy/envoy-rev0.json --restart-epoch 0 --drain-time-s 45 --parent-shutdown-time-s 60 --service-cluster sleep.default --service-node sidecar~10.80.3.109~sleep-856d589c9b-x6szk.default~default.svc.cluster.local --local-address-ip-version v4 --log-format-prefix-with-location 0 --log-format %Y-%m-%dT%T.%fZ.%l.envoy %n.%v -l warning --component-log-level misc:error --concurrency 2

Envoy架构

Envoy对入站/出站请求的处理过程如下，Envoy按照如下顺序依次在各个过滤器中处理请求。

Pilot-agent生成的初始配置文件

pilot-agent根据启动参数和K8S API Server中的配置信息生成Envoy的bootstrap文件(/etc/istio/proxy/envoy-rev0.json)，并负责启动Envoy进程(可以看到Envoy进程的父进程是pilot-agent)；envoy会通过xDS接口从istiod动态获取配置文件。envoy-rev0.json初始配置文件结构如下：

node：给出了Envoy 实例的信息

  "node": {
    "id": "sidecar~10.80.3.109~sleep-856d589c9b-x6szk.default~default.svc.cluster.local",
    "cluster": "sleep.default",
    "locality": {
    },
    "metadata": {"APP_CONTAINERS":"sleep,istio-proxy","CLUSTER_ID":"Kubernetes","EXCHANGE_KEYS":"NAME,NAMESPACE,INSTANCE_IPS,LABELS,OWNER,PLATFORM_METADATA,WORKLOAD_NAME,MESH_ID,SERVICE_ACCOUNT,CLUSTER_ID","INSTANCE_IPS":"10.80.3.109,fe80::40fb:daff:feed:e56c","INTERCEPTION_MODE":"REDIRECT","ISTIO_PROXY_SHA":"istio-proxy:f642a7fd07d0a99944a6e3529566e7985829839c","ISTIO_VERSION":"1.7.0","LABELS":{"app":"sleep","istio.io/rev":"default","pod-template-hash":"856d589c9b","security.istio.io/tlsMode":"istio","service.istio.io/canonical-name":"sleep","service.istio.io/canonical-revision":"latest"},"MESH_ID":"cluster.local","NAME":"sleep-856d589c9b-x6szk","NAMESPACE":"default","OWNER":"kubernetes://apis/apps/v1/namespaces/default/deployments/sleep","POD_PORTS":"[{\"name\":\"http-envoy-prom\",\"containerPort\":15090,\"protocol\":\"TCP\"}]","PROXY_CONFIG":{"binaryPath":"/usr/local/bin/envoy","concurrency":2,"configPath":"./etc/istio/proxy","controlPlaneAuthPolicy":"MUTUAL_TLS","discoveryAddress":"istiod.istio-system.svc:15012","drainDuration":"45s","envoyAccessLogService":{},"envoyMetricsService":{},"parentShutdownDuration":"60s","proxyAdminPort":15000,"proxyMetadata":{"DNS_AGENT":""},"serviceCluster":"sleep.default","statNameLength":189,"statusPort":15020,"terminationDrainDuration":"5s","tracing":{"zipkin":{"address":"zipkin.istio-system:9411"}}},"SDS":"true","SERVICE_ACCOUNT":"sleep","WORKLOAD_NAME":"sleep","k8s.v1.cni.cncf.io/networks":"istio-cni","sidecar.istio.io/interceptionMode":"REDIRECT","sidecar.istio.io/status":"{\"version\":\"8e6e902b765af607513b28d284940ee1421e9a0d07698741693b2663c7161c11\",\"initContainers\":[\"istio-validation\"],\"containers\":[\"istio-proxy\"],\"volumes\":[\"istio-envoy\",\"istio-data\",\"istio-podinfo\",\"istiod-ca-cert\"],\"imagePullSecrets\":null}","traffic.sidecar.istio.io/excludeInboundPorts":"15020","traffic.sidecar.istio.io/includeOutboundIPRanges":"*"}
  },

admin：给出了Envoy的日志路径和管理端口，例如可以通过curl -X POST localhost:15000/logging?level=trace设置日志级别为trace。

  "admin": {
    "access_log_path": "/dev/null", /* 管理服务器的访问日志路径 */
    "profile_path": "/var/lib/istio/data/envoy.prof", /* 管理服务器的CPU输出路径 */
    "address": { /* 管理服务器监听的TCP地址 */
      "socket_address": {
        "address": "127.0.0.1",
        "port_value": 15000
      }
    }
  },

dynamic_resources：配置动态资源，用于配置lds_config，cds_config和ads_config

Envoy通过xds-grpc cluster(参见static_resources)来获得xDS服务的地址。

  "dynamic_resources": {
    "lds_config": { /* 通过一个LDS配置Listeners */
      "ads": {},
      "resource_api_version": "V3" /* LDS使用的API版本号 */
    },
    "cds_config": { /* 通过一个CDS配置Cluster */
      "ads": {},
      "resource_api_version": "V3"
    },
    "ads_config": { /* API配置资源，用于指定API类型和Envoy获取xDS API的cluster */
      "api_type": "GRPC", /* 使用GRPC获取xDS信息 */
      "transport_api_version": "V3", /* xDS传输协议的版本号 */
      "grpc_services": [
        {
          "envoy_grpc": {
            "cluster_name": "xds-grpc" /* 动态获取xDS配置的cluster */
          }
        }
      ]
    }
  },

static_resources：配置静态资源，主要包括clusters和listeners两种资源：

Istio中的流量配置

clusters：下面给出了几个静态配置的cluster。

    "clusters": [
      {
        "name": "prometheus_stats", /* 使用Prometheus暴露metrics，接口为127.0.0.1:15000/stats/prometheus */
        "type": "STATIC", /* 明确指定上游host的网络名(IP地址/端口等) */
        "connect_timeout": "0.250s",
        "lb_policy": "ROUND_ROBIN",
        "load_assignment": { /* 仅用于类型为STATIC, STRICT_DNS或LOGICAL_DNS，用于给非EDS的clyster内嵌与EDS等同的endpoint */
          "cluster_name": "prometheus_stats", 
          "endpoints": [{
            "lb_endpoints": [{ /* 负载均衡的后端 */
              "endpoint": {
                "address":{
                  "socket_address": {
                    "protocol": "TCP",
                    "address": "127.0.0.1",
                    "port_value": 15000
                  }
                }
              }
            }]
          }]
        }
      },
      {
        "name": "agent", /* 暴露健康检查接口，可以使用curl http://127.0.0.1:15020/healthz/ready -v查看 */
        "type": "STATIC",
        "connect_timeout": "0.250s",
        "lb_policy": "ROUND_ROBIN",
        "load_assignment": {
          "cluster_name": "prometheus_stats",
          "endpoints": [{
            "lb_endpoints": [{ /* 负载均衡的后端 */
              "endpoint": {
                "address":{
                  "socket_address": {
                    "protocol": "TCP",
                    "address": "127.0.0.1",
                    "port_value": 15020
                  }
                }
              }
            }]
          }]
        }
      },
      {
        "name": "sds-grpc", /* 配置SDS cluster */
        "type": "STATIC",
        "http2_protocol_options": {},
        "connect_timeout": "1s",
        "lb_policy": "ROUND_ROBIN",
        "load_assignment": {
          "cluster_name": "sds-grpc",
          "endpoints": [{
            "lb_endpoints": [{
              "endpoint": {
                "address":{
                  "pipe": {
                    "path": "./etc/istio/proxy/SDS" /* 进行SDS的UNIX socket路径，用于在mTLS期间给istio-agent和proxy提供通信 */
                  }
                }
              }
            }]
          }]
        }
      },
      {
        "name": "xds-grpc", /* 动态xDS使用的grpc服务器配置 */
        "type": "STRICT_DNS",
        "respect_dns_ttl": true,
        "dns_lookup_family": "V4_ONLY",
        "connect_timeout": "1s",
        "lb_policy": "ROUND_ROBIN",
        "transport_socket": { /* 配置与上游连接的传输socket */
          "name": "envoy.transport_sockets.tls", /* 需要实例化的传输socket名称 */
          "typed_config": {
            "@type": "type.googleapis.com/envoy.extensions.transport_sockets.tls.v3.UpstreamTlsContext",
            "sni": "istiod.istio-system.svc", /* 创建TLS后端(即SDS服务器)连接时要使用的SNI字符串 */
            "common_tls_context": { /* 配置client和server使用的TLS上下文 */
              "alpn_protocols": [/* listener暴露的ALPN协议列表，如果为空，则不使用APPN */
                "h2"
              ],
              "tls_certificate_sds_secret_configs": [/*通过SDS API获取TLS证书的配置 */
                {
                  "name": "default",
                  "sds_config": { /* 配置sds_config时将会从静态资源加载secret */
                    "resource_api_version": "V3", /* xDS的API版本 */
                    "initial_fetch_timeout": "0s",
                    "api_config_source": { /* SDS API配置，如版本和SDS服务 */
                      "api_type": "GRPC",
                      "transport_api_version": "V3", /* xDS传输协议的API版本 */
                      "grpc_services": [
                        { /* SDS服务器对应上面配置的sds-grpc cluster */
                          "envoy_grpc": { "cluster_name": "sds-grpc" }
                        }
                      ]
                    }
                  }
                }
              ],
              "validation_context": {
                "trusted_ca": {
                  "filename": "./var/run/secrets/istio/root-cert.pem" /* 本地文件系统的数据源。挂载当前命名空间下的config istio-ca-root-cert，其中的CA证书与istio-system命名空间下的istio-ca-secret中的CA证书相同，用于校验对端istiod的证书 */
                },
                "match_subject_alt_names": [{"exact":"istiod.istio-system.svc"}] /* 验证证书中的SAN，即来自istiod的证书 */
              }
            }
          }
        },
        "load_assignment": {
          "cluster_name": "xds-grpc", /* 可以看到xds-grpc的后端为istiod的15012端口 */
          "endpoints": [{
            "lb_endpoints": [{
              "endpoint": {
                "address":{
                  "socket_address": {"address": "istiod.istio-system.svc", "port_value": 15012}
                }
              }
            }]
          }]
        },
        "circuit_breakers": { /* 断路器配置 */
          "thresholds": [
            {
              "priority": "DEFAULT",
              "max_connections": 100000,
              "max_pending_requests": 100000,
              "max_requests": 100000
            },
            {
              "priority": "HIGH",
              "max_connections": 100000,
              "max_pending_requests": 100000,
              "max_requests": 100000
            }
          ]
        },
        "upstream_connection_options": {
          "tcp_keepalive": {
            "keepalive_time": 300
          }
        },
        "max_requests_per_connection": 1,
        "http2_protocol_options": { }
      }
              ,
      {
        "name": "zipkin", /* 分布式链路跟踪zipkin的cluster配置 */
        "type": "STRICT_DNS",
        "respect_dns_ttl": true,
        "dns_lookup_family": "V4_ONLY",
        "connect_timeout": "1s",
        "lb_policy": "ROUND_ROBIN",
        "load_assignment": {
          "cluster_name": "zipkin",
          "endpoints": [{
            "lb_endpoints": [{
              "endpoint": {
                "address":{
                  "socket_address": {"address": "zipkin.istio-system", "port_value": 9411}
                }
              }
            }]
          }]
        }
      }
    ],

上面使用type.googleapis.com/envoy.extensions.transport_sockets.tls.v3.UpstreamTlsContext API接口来对传输socket进行配置，sni和common_tls_context 都属于结构体UpstreamTlsContext中的成员变量。

可以使用istioctl pc cluster命令查看静态cluster资源，第一列对应上面的Cluster.name，其中sds-grpc用于提供SDS服务，SDS的原理可以参见官方文档。

# istioctl pc cluster sleep-856d589c9b-x6szk.default |grep STATIC
BlackHoleCluster                        -         -          -             STATIC
agent                                   -         -          -             STATIC
prometheus_stats                        -         -          -             STATIC
sds-grpc                                -         -          -             STATIC
sleep.default.svc.cluster.local         80        http       inbound       STATIC

listener，下面用到了Network filter中的HTTP connection manager

    "listeners":[
      {
        "address": { /* listener监听的地址 */
          "socket_address": {
            "protocol": "TCP",
            "address": "0.0.0.0",
            "port_value": 15090
          }
        },
        "filter_chains": [
          {
            "filters": [
              {
                "name": "envoy.http_connection_manager",
                "typed_config": { /* 对扩展API的配置 */
                  "@type": "type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager",
                  "codec_type": "AUTO", /* 由连接管理器判断使用哪种编解码器 */
                  "stat_prefix": "stats",
                  "route_config": { /* 连接管理器的静态路由表 */
                    "virtual_hosts": [ /* 路由表使用的虚拟主机列表 */
                      {
                        "name": "backend", /* 路由表使用的虚拟主机 */
                        "domains": [ /* 匹配该虚拟主机的域列表 */
                          "*"
                        ],
                        "routes": [ /* 匹配入请求的路由列表，使用第一个匹配的路由 */
                          {
                            "match": { /* 将HTTP地址为/stats/prometheus的请求路由到cluster prometheus_stats */
                              "prefix": "/stats/prometheus" 
                            },
                            "route": {
                              "cluster": "prometheus_stats"
                            }
                          }
                        ]
                      }
                    ]
                  },
                  "http_filters": [{ /* 构成filter链的filter，用于处理请求。此处并没有定义任何规则 */
                    "name": "envoy.router",
                    "typed_config": {
                      "@type": "type.googleapis.com/envoy.extensions.filters.http.router.v3.Router"
                    }
                  }]
                }
              }
            ]
          }
        ]
      },
      {
        "address": {
          "socket_address": {
            "protocol": "TCP",
            "address": "0.0.0.0",
            "port_value": 15021
          }
        },
        "filter_chains": [
          {
            "filters": [
              {
                "name": "envoy.http_connection_manager",
                "typed_config": {
                  "@type": "type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager",
                  "codec_type": "AUTO",
                  "stat_prefix": "agent",
                  "route_config": { /* 静态路由表配置 */
                    "virtual_hosts": [
                      {
                        "name": "backend",
                        "domains": [
                          "*"
                        ],
                        "routes": [
                          {
                            "match": { /* 将HTTP地址为/healthz/ready的请求路由到cluster agent */
                              "prefix": "/healthz/ready"
                            },
                            "route": {
                              "cluster": "agent"
                            }
                          }
                        ]
                      }
                    ]
                  },
                  "http_filters": [{
                    "name": "envoy.router",
                    "typed_config": {
                      "@type": "type.googleapis.com/envoy.extensions.filters.http.router.v3.Router"
                    }
                  }]
                }
              }
            ]
          }
        ]
      }
    ]
  }

tracing，对应上面static_resources里定义的zipkin cluster。

  "tracing": {
    "http": {
      "name": "envoy.zipkin",
      "typed_config": {
        "@type": "type.googleapis.com/envoy.config.trace.v3.ZipkinConfig",
        "collector_cluster": "zipkin",
        "collector_endpoint": "/api/v2/spans",
        "collector_endpoint_version": "HTTP_JSON",
        "trace_id_128bit": true,
        "shared_span_context": false
      }
    }
  }

基本流程如下：

Istio中的流量配置

Envoy管理接口获取的完整配置

可以在注入Envoy sidecar的pod中执行curl -X POST localhost:15000/config_dump来获取完整的配置信息。可以看到它主要包含BootstrapConfig，ClustersConfig，ListenersConfig，RoutesConfig，SecretsConfig这5部分。

Bootstrap：它与上面由Pilot-agent生成的envoy-rev0.json文件中的内容相同，即提供给Envoy proxy的初始化配置，给出了xDS服务器的地址等信息。

Clusters：在Envoy中，Cluster是一个服务集群，每个cluster包含一个或多个endpoint(可以将cluster近似看作是k8s中的service)。

从上图可以看出，ClustersConfig包含两种cluster配置：static_clusters和dynamic_active_clusters。前者中的cluster来自envoy-rev0.json中配置的静态cluster资源，包含agent，prometheus_stats，sds-grpc，xds-grpc和zipkin；后者是通过xDS接口从istio的控制面获取的动态配置信息，dynamic_active_clusters主要分为如下四种类型：

BlackHoleCluster：

     "cluster": {
      "@type": "type.googleapis.com/envoy.config.cluster.v3.Cluster",
      "name": "BlackHoleCluster", /* cluster名称 */
      "type": "STATIC",
      "connect_timeout": "10s",
      "filters": [ /* 出站连接的过滤器配置 */
       {
        "name": "istio.metadata_exchange",
        "typed_config": { /* 对扩展API的配置 */
         "@type": "type.googleapis.com/udpa.type.v1.TypedStruct",
         "type_url": "type.googleapis.com/envoy.tcp.metadataexchange.config.MetadataExchange",
         "value": {
          "protocol": "istio-peer-exchange"
         }
        }
       }
      ]
     },

BlackHoleCluster使用的API类型为type.googleapis.com/udpa.type.v1.TypedStruct，表示控制面缺少缺少该扩展的模式定义，client会使用type_url指定的API，将内容转换为类型化的配置资源。

在上面可以看到Istio使用了协议istio-peer-exchange ，服务网格内部的两个Envoy实例之间使用该协议来交互Node Metadata。NodeMetadata的数据结构如下：

type NodeMetadata struct {
	// ProxyConfig defines the proxy config specified for a proxy.
	// Note that this setting may be configured different for each proxy, due user overrides
	// or from different versions of proxies connecting. While Pilot has access to the meshConfig.defaultConfig,
	// this field should be preferred if it is present.
	ProxyConfig *NodeMetaProxyConfig `json:"PROXY_CONFIG,omitempty"`

	// IstioVersion specifies the Istio version associated with the proxy
	IstioVersion string `json:"ISTIO_VERSION,omitempty"`

	// Labels specifies the set of workload instance (ex: k8s pod) labels associated with this node.
	Labels map[string]string `json:"LABELS,omitempty"`

	// InstanceIPs is the set of IPs attached to this proxy
	InstanceIPs StringList `json:"INSTANCE_IPS,omitempty"`

	// Namespace is the namespace in which the workload instance is running.
	Namespace string `json:"NAMESPACE,omitempty"`

	// InterceptionMode is the name of the metadata variable that carries info about
	// traffic interception mode at the proxy
	InterceptionMode TrafficInterceptionMode `json:"INTERCEPTION_MODE,omitempty"`

	// ServiceAccount specifies the service account which is running the workload.
	ServiceAccount string `json:"SERVICE_ACCOUNT,omitempty"`

	// RouterMode indicates whether the proxy is functioning as a SNI-DNAT router
	// processing the AUTO_PASSTHROUGH gateway servers
	RouterMode string `json:"ROUTER_MODE,omitempty"`

	// MeshID specifies the mesh ID environment variable.
	MeshID string `json:"MESH_ID,omitempty"`

	// ClusterID defines the cluster the node belongs to.
	ClusterID string `json:"CLUSTER_ID,omitempty"`

	// Network defines the network the node belongs to. It is an optional metadata,
	// set at injection time. When set, the Endpoints returned to a note and not on same network
	// will be replaced with the gateway defined in the settings.
	Network string `json:"NETWORK,omitempty"`

	// RequestedNetworkView specifies the networks that the proxy wants to see
	RequestedNetworkView StringList `json:"REQUESTED_NETWORK_VIEW,omitempty"`

	// PodPorts defines the ports on a pod. This is used to lookup named ports.
	PodPorts PodPortList `json:"POD_PORTS,omitempty"`

	// TLSServerCertChain is the absolute path to server cert-chain file
	TLSServerCertChain string `json:"TLS_SERVER_CERT_CHAIN,omitempty"`
	// TLSServerKey is the absolute path to server private key file
	TLSServerKey string `json:"TLS_SERVER_KEY,omitempty"`
	// TLSServerRootCert is the absolute path to server root cert file
	TLSServerRootCert string `json:"TLS_SERVER_ROOT_CERT,omitempty"`
	// TLSClientCertChain is the absolute path to client cert-chain file
	TLSClientCertChain string `json:"TLS_CLIENT_CERT_CHAIN,omitempty"`
	// TLSClientKey is the absolute path to client private key file
	TLSClientKey string `json:"TLS_CLIENT_KEY,omitempty"`
	// TLSClientRootCert is the absolute path to client root cert file
	TLSClientRootCert string `json:"TLS_CLIENT_ROOT_CERT,omitempty"`

	CertBaseDir string `json:"BASE,omitempty"`

	// IdleTimeout specifies the idle timeout for the proxy, in duration format (10s).
	// If not set, no timeout is set.
	IdleTimeout string `json:"IDLE_TIMEOUT,omitempty"`

	// HTTP10 indicates the application behind the sidecar is making outbound http requests with HTTP/1.0
	// protocol. It will enable the "AcceptHttp_10" option on the http options for outbound HTTP listeners.
	// Alpha in 1.1, based on feedback may be turned into an API or change. Set to "1" to enable.
	HTTP10 string `json:"HTTP10,omitempty"`

	// Generator indicates the client wants to use a custom Generator plugin.
	Generator string `json:"GENERATOR,omitempty"`

	// DNSCapture indicates whether the workload has enabled dns capture
	DNSCapture string `json:"DNS_CAPTURE,omitempty"`

	// ProxyXDSViaAgent indicates that xds data is being proxied via the agent
	ProxyXDSViaAgent string `json:"PROXY_XDS_VIA_AGENT,omitempty"`

	// Contains a copy of the raw metadata. This is needed to lookup arbitrary values.
	// If a value is known ahead of time it should be added to the struct rather than reading from here,
	Raw map[string]interface{} `json:"-"`
}

Istio通过一些特定的TCP属性来启用TCP策略和控制(这些属性由Envoy代理生成)，并通过Envoy的Node Metadata来获取这些属性。Envoy使用ALPN隧道和基于前缀的协议来转发Node Metadata到对端的Envoy。Istio定义了一个新的协议istio-peer-exchange，由网格中的客户端和服务端的sidecar在TLS协商时进行宣告并确定优先级。启用istio代理的两端会通过ALPN协商将协议解析为istio-peer-exchange(因此仅限于istio服务网格内的交互)，后续的TCP交互将会按照istio-peer-exchange的协议规则进行交互：

Istio中的流量配置

使用如下命令可以看到cluster BlackHoleCluster是没有endpoint的。

# istioctl pc endpoint sleep-856d589c9b-x6szk.default --cluster BlackHoleCluster
ENDPOINT     STATUS     OUTLIER CHECK     CLUSTER

如下内容参考官方博客：

对于外部服务，Istio提供了两种管理方式：通过将global.outboundTrafficPolicy.mode 设置为REGISTRY_ONLY来block所有到外部服务的访问；以及通过将global.outboundTrafficPolicy.mode设置为ALLOW_ANY来允许所有到外部服务的访问。默认会允许所有到外部服务的访问。

BlackHoleCluster ：当global.outboundTrafficPolicy.mode设置为REGISTRY_ONLY时，Envoy会创建一个虚拟的cluster BlackHoleCluster。该模式下，所有到外部服务的访问都会被block(除非为每个服务添加service entries)。为了实现该功能，默认的outbound listener(监听地址为 0.0.0.0:15001)使用原始目的地来设置TCP代理，BlackHoleCluster 作为一个静态cluster。由于BlackHoleCluster 没有任何endpoint，因此会丢弃所有到外部的流量。此外，Istio会为平台服务的每个端口/协议组合创建唯一的listener，如果对同一端口的外部服务发起请求，则不会命中虚拟listener。这种情况会对route配置进行扩展，添加到BlackHoleCluster的路由。如果没有匹配到其他路由，则Envoy代理会直接返回502 HTTP状态码(BlackHoleCluster可以看作是路由黑洞)。
       {
        "name": "block_all",
        "domains": [
         "*"
        ],
        "routes": [
         {
          "match": {
           "prefix": "/"
          },
          "direct_response": {
           "status": 502
          },
          "name": "block_all"
         }
        ],
        "include_request_attempt_count": true
       },

PassthroughCluster：可以看到PassthroughCluster也使用了istio-peer-exchange协议来处理TCP。

     "cluster": {
      "@type": "type.googleapis.com/envoy.config.cluster.v3.Cluster",
      "name": "PassthroughCluster",
      "type": "ORIGINAL_DST", /* 指定type为ORIGINAL_DST，这是一个特殊的cluster */
      "connect_timeout": "10s",
      "lb_policy": "CLUSTER_PROVIDED",
      "circuit_breakers": {
       "thresholds": [
        {
         "max_connections": 4294967295,
         "max_pending_requests": 4294967295,
         "max_requests": 4294967295,
         "max_retries": 4294967295
        }
       ]
      },
      "protocol_selection": "USE_DOWNSTREAM_PROTOCOL",
      "filters": [
       {
        "name": "istio.metadata_exchange", /* 配置使用ALPN istio-peer-exchange协议来交换Node Metadata */
        "typed_config": {
         "@type": "type.googleapis.com/udpa.type.v1.TypedStruct",
         "type_url": "type.googleapis.com/envoy.tcp.metadataexchange.config.MetadataExchange",
         "value": {
          "protocol": "istio-peer-exchange"
         }
        }
       }
      ]
     },

使用如下命令可以看到cluster PassthroughCluster是没有endpoint的。

# istioctl pc endpoint sleep-856d589c9b-x6szk.default --cluster PassthroughCluster
ENDPOINT     STATUS     OUTLIER CHECK     CLUSTER

PassthroughCluster ：当global.outboundTrafficPolicy.mode设置为ALLOW_ANY时，Envoy会创建一个虚拟的cluster PassthroughCluster 。该模式下，会允许所有到外部服务的访问。为了实现该功能，默认的outbound listener(监听地址为 0.0.0.0:15001)使用SO_ORIGINAL_DST来配置TCP Proxy，PassthroughCluster作为一个静态cluster。

PassthroughCluster cluster使用原始目的地负载均衡策略来配置Envoy发送到原始目的地的流量。

与BlackHoleCluster类似，对于每个基于端口/协议的listener，都会添加虚拟路由，将PassthroughCluster作为为默认路由。
   {
    "name": "allow_any",
    "domains": [
     "*"
    ],
    "routes": [
     {
      "match": {
       "prefix": "/"
      },
      "route": {
       "cluster": "PassthroughCluster",
       "timeout": "0s",
       "max_grpc_timeout": "0s"
      },
      "name": "allow_any"
     }
    ],
    "include_request_attempt_count": true
   },

由于global.outboundTrafficPolicy.mode只能配置某一个值，因此BlackHoleCluster和PassthroughCluster的出现是互斥的，BlackHoleCluster和PassthroughCluster的路由仅存在istio服务网格内，即注入sidecar的pod中。

可以使用Prometheus metrics来监控到BlackHoleCluster和PassthroughCluster的访问。

inbound cluster：处理入站请求的cluster，对于下面的sleep应用来说，其只有一个本地后端127.0.0.1:80，并通过load_assignment指定了cluster名称和负载信息。由于该监听器上的流量不会出战，因此下面并没有配置过滤器。

 "cluster": {
  "@type": "type.googleapis.com/envoy.config.cluster.v3.Cluster",
  "name": "inbound|80|http|sleep.default.svc.cluster.local",
  "type": "STATIC",
  "connect_timeout": "10s",
  "circuit_breakers": {
   "thresholds": [
    {
     "max_connections": 4294967295,
     "max_pending_requests": 4294967295,
     "max_requests": 4294967295,
     "max_retries": 4294967295
    }
   ]
  },
  "load_assignment": { /* 设置入站的cluster的endpoint的负载均衡 */
   "cluster_name": "inbound|80|http|sleep.default.svc.cluster.local",
   "endpoints": [
    {
     "lb_endpoints": [
      {
       "endpoint": {
        "address": {
         "socket_address": {
          "address": "127.0.0.1",
          "port_value": 80
         }
        }
       }
      }
     ]
    }
   ]
  }
 },

也可以使用如下命令查看inbound的cluster信息：

# istioctl pc cluster sleep-856d589c9b-c6xsm.default --direction inbound
SERVICE FQDN                        PORT     SUBSET     DIRECTION     TYPE       DESTINATION RULE
sleep.default.svc.cluster.local     80       http       inbound       STATIC

outbound cluster：这类cluster为Envoy节点外的服务，配置如何连接上游。下面的EDS表示该cluster的endpoint来自EDS服务发现。下面给出的outbound cluster是istiod的15012端口上的服务。基本结构如下，transport_socket_matches仅在使用TLS才会出现，用于配置与TLS证书相关的信息。

Istio中的流量配置

具体内容如下：

{
 "version_info": "2020-09-15T08:05:54Z/4",
 "cluster": {
  "@type": "type.googleapis.com/envoy.config.cluster.v3.Cluster",
  "name": "outbound|15012||istiod.istio-system.svc.cluster.local",
  "type": "EDS", 
  "eds_cluster_config": { /* EDS的配置 */
   "eds_config": {
    "ads": {},
    "resource_api_version": "V3"
   },
   "service_name": "outbound|15012||istiod.istio-system.svc.cluster.local" /* EDS的cluster的可替代名称，无需与cluster名称完全相同 */
  },
  "connect_timeout": "10s",
  "circuit_breakers": { /* 断路器设置 */
   "thresholds": [
    {
     "max_connections": 4294967295,
     "max_pending_requests": 4294967295,
     "max_requests": 4294967295,
     "max_retries": 4294967295
    }
   ]
  },
  "filters": [ /* 设置Node Metadata交互使用的协议为istio-peer-exchange */
   {
    "name": "istio.metadata_exchange",
    "typed_config": {
     "@type": "type.googleapis.com/udpa.type.v1.TypedStruct",
     "type_url": "type.googleapis.com/envoy.tcp.metadataexchange.config.MetadataExchange",
     "value": {
      "protocol": "istio-peer-exchange"
     }
    }
   }
  ],
  "transport_socket_matches": [ /* 指定匹配的后端使用的带TLS的传输socket */
   {
    "name": "tlsMode-istio", /* match的名称 */
    "match": { /* 匹配后端的条件，注入istio sidecar的pod会打上标签：security.istio.io/tlsMode=istio */
     "tlsMode": "istio"
    },
    "transport_socket": { /* 匹配cluster的后端使用的传输socket的配置 */
     "name": "envoy.transport_sockets.tls",
     "typed_config": {
      "@type": "type.googleapis.com/envoy.extensions.transport_sockets.tls.v3.UpstreamTlsContext",
      "common_tls_context": { /* 配置client和server端使用的TLS上下文 */
       "alpn_protocols": [ /* 配置交互使用的ALPN协议集，供上游选择 */
        "istio-peer-exchange",
        "istio"
       ],
       "tls_certificate_sds_secret_configs": [ /* 通过SDS API获取TLS证书的配置 */
        {
         "name": "default",
         "sds_config": {
          "api_config_source": {
           "api_type": "GRPC",
           "grpc_services": [ /* SDS的cluster */
            {
             "envoy_grpc": {
              "cluster_name": "sds-grpc" /* 为上面静态配置的cluster */
             }
            }
           ],
           "transport_api_version": "V3"
          },
          "initial_fetch_timeout": "0s",
          "resource_api_version": "V3"
         }
        }
       ],
       "combined_validation_context": { /* 包含一个CertificateValidationContext(即下面的default_validation_context)和SDS配置。当SDS服务返回动态的CertificateValidationContext时，动态和默认的CertificateValidationContext会合并为一个新的CertificateValidationContext来进行校验  */
        "default_validation_context": { /* 配置如何认证对端istiod服务的证书 */
         "match_subject_alt_names": [ /* Envoy会按照如下配置来校验证书中的SAN */
          {
           "exact": "spiffe://new-td/ns/istio-system/sa/istiod-service-account" /* 与Istio配置的serviceaccount授权策略相同 */
          }
         ]
        },
        "validation_context_sds_secret_config": { /* SDS配置，也是通过静态的cluster sds-grpc提供SDS API服务 */
         "name": "ROOTCA",
         "sds_config": {
          "api_config_source": {
           "api_type": "GRPC",
           "grpc_services": [
            {
             "envoy_grpc": {
              "cluster_name": "sds-grpc"
             }
            }
           ],
           "transport_api_version": "V3"
          },
          "initial_fetch_timeout": "0s",
          "resource_api_version": "V3"
         }
        }
       }
      },
      "sni": "outbound_.15012_._.istiod.istio-system.svc.cluster.local" /* 创建TLS连接时使用的SNI字符串，即TLS的server_name扩展字段中的值 */
     }
    }
   },
   {
    "name": "tlsMode-disabled", /* 如果与没有匹配到的后端(即istio服务网格外的后端)进行通信时，则使用明文方式 */
    "match": {},
    "transport_socket": {
     "name": "envoy.transport_sockets.raw_buffer"
    }
   }
  ]
 },
 "last_updated": "2020-09-15T08:06:23.565Z"
},

Listeners：Envoy使用listener来接收并处理下游发来的请求。与cluster类似，listener也分为静态和动态两种配置。静态配置来自Istio-agent生成的envoy-rev0.json文件。动态配置为：

virtualOutbound Listener：Istio在注入sidecar时，会通过init容器来设置iptables规则，将所有出站的TCP流量拦截到本地的15001端口：

-A ISTIO_REDIRECT -p tcp -j REDIRECT --to-ports 15001

一个istio-agent配置中仅包含一个virtualOutbound listener，可以看到该listener并没有配置transport_socket，它的下游流量就是来自本pod的业务容器，并不需要进行TLS校验，直接将流量重定向到15001端口即可，然后转发给和原始目的IP:Port匹配的listener。

    {
     "name": "virtualOutbound",
     "active_state": {
      "version_info": "2020-09-15T08:05:54Z/4",
      "listener": {
       "@type": "type.googleapis.com/envoy.config.listener.v3.Listener",
       "name": "virtualOutbound",
       "address": { /* 监听器监听的地址 */
        "socket_address": {
         "address": "0.0.0.0",
         "port_value": 15001
        }
       },
       "filter_chains": [ /* 应用到该监听器的过滤器链 */
        {
         "filters": [ /* 与该监听器建立连接时使用的过滤器，按顺序处理各个过滤器。如果过滤器列表为空，则默认会关闭连接 */
          {
           "name": "istio.stats",
           "typed_config": {
            "@type": "type.googleapis.com/udpa.type.v1.TypedStruct",
            "type_url": "type.googleapis.com/envoy.extensions.filters.network.wasm.v3.Wasm",
            "value": {
             "config": { /* Wasm插件配置 */
              "root_id": "stats_outbound", /* 一个VM中具有相同root_id的一组filters/services会共享相同的RootContext和Contexts，如果该字段为空，所有该字段为空的filters/services都会共享具有相同vm_id的Context(s) */
              "vm_config": { /* Wasm VM的配置 */
               "vm_id": "tcp_stats_outbound", /* 使用相同vm_id和code将使用相同的VM */
               "runtime": "envoy.wasm.runtime.null", /* Wasm运行时，v8或null */
               "code": {
                "local": {
                 "inline_string": "envoy.wasm.stats"
                }
               }
              },
              "configuration": {
               "@type": "type.googleapis.com/google.protobuf.StringValue",
               "value": "{\n  \"debug\": \"false\",\n  \"stat_prefix\": \"istio\"\n}\n"
              }
             }
            }
           }
          },
          {
           "name": "envoy.tcp_proxy", /* 处理TCP的过滤器 */
           "typed_config": {
            "@type": "type.googleapis.com/envoy.extensions.filters.network.tcp_proxy.v3.TcpProxy",
            "stat_prefix": "PassthroughCluster",
            "cluster": "PassthroughCluster", /* 连接的上游cluster */
            "access_log": [
             {
              "name": "envoy.file_access_log",
              "typed_config": { /* 配置日志的输出格式和路径 */
               "@type": "type.googleapis.com/envoy.extensions.access_loggers.file.v3.FileAccessLog",
               "path": "/dev/stdout",
               "format": "[%START_TIME%] \"%REQ(:METHOD)% %REQ(X-ENVOY-ORIGINAL-PATH?:PATH)% %PROTOCOL%\" %RESPONSE_CODE% %RESPONSE_FLAGS% \"%DYNAMIC_METADATA(istio.mixer:status)%\" \"%UPSTREAM_TRANSPORT_FAILURE_REASON%\" %BYTES_RECEIVED% %BYTES_SENT% %DURATION% %RESP(X-ENVOY-UPSTREAM-SERVICE-TIME)% \"%REQ(X-FORWARDED-FOR)%\" \"%REQ(USER-AGENT)%\" \"%REQ(X-REQUEST-ID)%\" \"%REQ(:AUTHORITY)%\" \"%UPSTREAM_HOST%\" %UPSTREAM_CLUSTER% %UPSTREAM_LOCAL_ADDRESS% %DOWNSTREAM_LOCAL_ADDRESS% %DOWNSTREAM_REMOTE_ADDRESS% %REQUESTED_SERVER_NAME% %ROUTE_NAME%\n"
              }
             }
            ]
           }
          }
         ],
         "name": "virtualOutbound-catchall-tcp"
        }
       ],
       "hidden_envoy_deprecated_use_original_dst": true,
       "traffic_direction": "OUTBOUND"
      },
      "last_updated": "2020-09-15T08:06:24.066Z"
     }
    },

上面envoy.tcp_proxy过滤器的cluster为PassthroughCluster，这是因为将global.outboundTrafficPolicy.mode设置为了ALLOW_ANY，默认可以访问外部服务。如果global.outboundTrafficPolicy.mode设置为了REGISTRY_ONLY，则此处将变为cluster BlackHoleCluster，默认丢弃所有到外部服务的请求。

上面使用wasm(WebAssembly)来记录遥测信息，Envoy官方文档中目前缺少对wasm的描述，可以参考开源代码的描述。从runtime字段为null可以看到并没有启用。可以在安装istio的时候使用如下参数来启用基于Wasm的遥测。
$ istioctl install --set values.telemetry.v2.metadataExchange.wasmEnabled=true --set values.telemetry.v2.prometheus.wasmEnabled=true
启用之后，与wasm有关的用于遥测的过滤器配置变为了如下内容，可以看到其runtime使用了envoy.wasm.runtime.v8。更多参见官方博客。
          {
           "name": "istio.stats",
           "typed_config": {
            "@type": "type.googleapis.com/udpa.type.v1.TypedStruct",
            "type_url": "type.googleapis.com/envoy.extensions.filters.network.wasm.v3.Wasm",
            "value": {
             "config": {
              "root_id": "stats_outbound",
              "vm_config": { /* wasm虚拟机配置 */
               "vm_id": "tcp_stats_outbound",
               "runtime": "envoy.wasm.runtime.v8", /* 使用的wasm runtime */
               "code": {
                "local": {
                 "filename": "/etc/istio/extensions/stats-filter.compiled.wasm" /* 编译后的wasm插件路径 */
                }
               },
               "allow_precompiled": true
              },
              "configuration": {
               "@type": "type.googleapis.com/google.protobuf.StringValue",
               "value": "{\n  \"debug\": \"false\",\n  \"stat_prefix\": \"istio\"\n}\n"
              }
             }
            }
           }
          },
在istio-proxy容器的/etc/istio/extensions/目录下可以看到wasm编译的相关程序，包含用于交换Node Metadata的metadata-exchange-filter.wasm和用于遥测的stats-filter.wasm，带compiled的wasm用于HTTP。
$ ls
metadata-exchange-filter.compiled.wasm  metadata-exchange-filter.wasm  stats-filter.compiled.wasm  stats-filter.wasm
Istio的filter处理示意图如下：

VirtualInbound/Inbound Listener：与virtualOutbound listener类似，通过如下规则将所有入站的TCP流量重定向到15006端口

-A ISTIO_IN_REDIRECT -p tcp -j REDIRECT --to-ports 15006

下面是一个demo环境中的典型配置，可以看到对于每个监听的地址，都配置了两个过滤器：一个带transport_socket，一个不带transport_socket，分别处理使用TLS的连接和不使用TLS的连接。主要的入站监听器为：

处理基于IPv4的带TLS 的TCP连接
处理基于IPv4的不带TLS 的TCP连接
处理基于IPv6的带TLS 的TCP连接
处理基于IPv6的不带TLS 的TCP连接
处理基于IPv4的带TLS 的HTTP连接
处理基于IPv4的不带TLS 的HTTP连接
处理基于IPv6的带TLS 的HTTP连接
处理基于IPv6的不带TLS 的HTTP连接
处理业务的带TLS(不带TLS)的连接

Istio中的流量配置

下面给出如下内容的inbound listener：

处理基于IPv4的带TLS 的TCP连接
处理基于IPv4的不带TLS 的TCP连接
处理业务的带TLS的连接

    {
     "name": "virtualInbound",
     "active_state": {
      "version_info": "2020-09-15T08:05:54Z/4",
      "listener": {
       "@type": "type.googleapis.com/envoy.config.listener.v3.Listener",
       "name": "virtualInbound",
       "address": { /* 该listener绑定的地址和端口 */
        "socket_address": {
         "address": "0.0.0.0",
         "port_value": 15006
        }
       },
       "filter_chains": [
        /* 匹配所有IPV4地址，使用TLS且ALPN为istio-peer-exchange或istio的连接 */
        {
         "filter_chain_match": { /* 将连接匹配到该过滤器链时使用的标准 */
          "prefix_ranges": [ /* 当listener绑定到0.0.0.0/::时匹配的IP地址和前缀长度，下面表示整个网络地址 */
           {
            "address_prefix": "0.0.0.0",
            "prefix_len": 0
           }
          ],
          "transport_protocol": "tls", /* 匹配的传输协议 */
          "application_protocols": [ /* 使用的ALPN */
           "istio-peer-exchange",
           "istio"
          ]
         },
         "filters": [
          {
           "name": "istio.metadata_exchange", /* 交换Node Metadata的配置 */
           "typed_config": {
            "@type": "type.googleapis.com/udpa.type.v1.TypedStruct",
            "type_url": "type.googleapis.com/envoy.tcp.metadataexchange.config.MetadataExchange",
            "value": {
             "protocol": "istio-peer-exchange"
            }
           }
          },
          {
           "name": "istio.stats", /* 使用wasm进行遥测的配置 */
           "typed_config": {
            "@type": "type.googleapis.com/udpa.type.v1.TypedStruct",
            "type_url": "type.googleapis.com/envoy.extensions.filters.network.wasm.v3.Wasm",
            "value": {
             "config": {
              "root_id": "stats_inbound",
              "vm_config": {
               "vm_id": "tcp_stats_inbound",
               "runtime": "envoy.wasm.runtime.null",
               "code": {
                "local": {
                 "inline_string": "envoy.wasm.stats"
                }
               }
              },
              "configuration": {
               "@type": "type.googleapis.com/google.protobuf.StringValue",
               "value": "{\n  \"debug\": \"false\",\n  \"stat_prefix\": \"istio\"\n}\n"
              }
             }
            }
           }
          },
          {
           "name": "envoy.tcp_proxy", /* 配置连接上游cluster InboundPassthroughClusterIpv4时的访问日志，InboundPassthroughClusterIpv4 cluster用于处理基于IPv4的HTTP */
           "typed_config": {
            "@type": "type.googleapis.com/envoy.extensions.filters.network.tcp_proxy.v3.TcpProxy",
            "stat_prefix": "InboundPassthroughClusterIpv4",
            "cluster": "InboundPassthroughClusterIpv4",
            "access_log": [
             {
              "name": "envoy.file_access_log",
              "typed_config": {
               "@type": "type.googleapis.com/envoy.extensions.access_loggers.file.v3.FileAccessLog",
               "path": "/dev/stdout",
               "format": "[%START_TIME%] \"%REQ(:METHOD)% %REQ(X-ENVOY-ORIGINAL-PATH?:PATH)% %PROTOCOL%\" %RESPONSE_CODE% %RESPONSE_FLAGS% \"%DYNAMIC_METADATA(istio.mixer:status)%\" \"%UPSTREAM_TRANSPORT_FAILURE_REASON%\" %BYTES_RECEIVED% %BYTES_SENT% %DURATION% %RESP(X-ENVOY-UPSTREAM-SERVICE-TIME)% \"%REQ(X-FORWARDED-FOR)%\" \"%REQ(USER-AGENT)%\" \"%REQ(X-REQUEST-ID)%\" \"%REQ(:AUTHORITY)%\" \"%UPSTREAM_HOST%\" %UPSTREAM_CLUSTER% %UPSTREAM_LOCAL_ADDRESS% %DOWNSTREAM_LOCAL_ADDRESS% %DOWNSTREAM_REMOTE_ADDRESS% %REQUESTED_SERVER_NAME% %ROUTE_NAME%\n"
              }
             }
            ]
           }
          }
         ],
         "transport_socket": { /* 匹配TLS的传输socket */
          "name": "envoy.transport_sockets.tls",
          "typed_config": {
           "@type": "type.googleapis.com/envoy.extensions.transport_sockets.tls.v3.DownstreamTlsContext",
           "common_tls_context": {
            "alpn_protocols": [ /* 监听器使用的ALPN列表 */
             "istio-peer-exchange",
             "h2",
             "http/1.1"
            ],
            "tls_certificate_sds_secret_configs": [ /* 通过SDS API获取证书的配置 */
             {
              "name": "default",
              "sds_config": {
               "api_config_source": {
                "api_type": "GRPC",
                "grpc_services": [
                 {
                  "envoy_grpc": {
                   "cluster_name": "sds-grpc"
                  }
                 }
                ],
                "transport_api_version": "V3"
               },
               "initial_fetch_timeout": "0s",
               "resource_api_version": "V3"
              }
             }
            ],
            "combined_validation_context": {
             "default_validation_context": { /* 对对端的证书的SAN进行认证 */
              "match_subject_alt_names": [ 
               {
                "prefix": "spiffe://new-td/"
               },
               {
                "prefix": "spiffe://old-td/"
               }
              ]
             },
             "validation_context_sds_secret_config": { /* 配置通过SDS API获取证书 */
              "name": "ROOTCA",
              "sds_config": {
               "api_config_source": {
                "api_type": "GRPC",
                "grpc_services": [
                 {
                  "envoy_grpc": {
                   "cluster_name": "sds-grpc"
                  }
                 }
                ],
                "transport_api_version": "V3"
               },
               "initial_fetch_timeout": "0s",
               "resource_api_version": "V3"
              }
             }
            }
           },
           "require_client_certificate": true
          }
         },
         "name": "virtualInbound"
        },
        /* 与上面不同的是，此处匹配不带TLS的连接 */
        {
         "filter_chain_match": {
          "prefix_ranges": [
           {
            "address_prefix": "0.0.0.0",
            "prefix_len": 0
           }
          ]
         },
         "filters": [
          {
           "name": "istio.metadata_exchange",
            ...
          },
          {
           "name": "istio.stats",
			...
          },
          {
           "name": "envoy.tcp_proxy",
            ...
          }
         ],
         "name": "virtualInbound"
        },
        ...
        /* 应用的监听器，监听端口为HTTP 80端口 */
        {
         "filter_chain_match": {
          "destination_port": 80, /* 匹配的请求的目的端口 */
          "application_protocols": [ /* 匹配的ALPN，仅在使用TLS时使用 */
           "istio",
           "istio-http/1.0",
           "istio-http/1.1",
           "istio-h2"
          ]
         },
         "filters": [
          {
           "name": "istio.metadata_exchange", /* 交换Node Metadata的配置 */
            ...
          },
          {
           "name": "envoy.http_connection_manager", /* HTTP连接管理过滤器 */
           "typed_config": {
            "@type": "type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager",
            "stat_prefix": "inbound_0.0.0.0_80",
            "route_config": { /* 静态路由表 */
             "name": "inbound|80|http|sleep.default.svc.cluster.local", /* 路由配置的名称 */
             "virtual_hosts": [ /* 构成路由表的虚拟主机列表 */
              {
               "name": "inbound|http|80", /* 构成路由表的虚拟主机名 */
               "domains": [ /* 匹配到该虚拟主机的域列表 */
                "*"
               ],
               "routes": [ /* 对入站请求的路由，将路径为"/"的HTTP请求路由到cluster inbound|80|http|sleep.default.svc.cluster.local*/
                {
                 "match": {
                  "prefix": "/"
                 },
                 "route": {
                  "cluster": "inbound|80|http|sleep.default.svc.cluster.local",
                  "timeout": "0s",
                  "max_grpc_timeout": "0s"
                 },
                 "decorator": {
                  "operation": "sleep.default.svc.cluster.local:80/*"
                 },
                 "name": "default" /* 路由的名称 */
                }
               ]
              }
             ],
             "validate_clusters": false
            },
            "http_filters": [ /* HTTP连接过滤器链 */
             {
              "name": "istio.metadata_exchange", /* 基于HTTP的Metadata的交换配置 */
			   ...
             },
             {
              "name": "istio_authn", /* istio的mTLS的默认值 */
              "typed_config": {
               "@type": "type.googleapis.com/istio.envoy.config.filter.http.authn.v2alpha1.FilterConfig",
               "policy": {
                "peers": [
                 {
                  "mtls": {
                   "mode": "PERMISSIVE"
                  }
                 }
                ]
               },
               "skip_validate_trust_domain": true
              }
             },
             {
              "name": "envoy.filters.http.cors",
              "typed_config": {
               "@type": "type.googleapis.com/envoy.extensions.filters.http.cors.v3.Cors"
              }
             },
             {
              "name": "envoy.fault",
              "typed_config": {
               "@type": "type.googleapis.com/envoy.extensions.filters.http.fault.v3.HTTPFault"
              }
             },
             {
              "name": "istio.stats", /* 基于HTTP的遥测配置 */
               ...
             },
             {
              "name": "envoy.router",
              "typed_config": {
               "@type": "type.googleapis.com/envoy.extensions.filters.http.router.v3.Router"
              }
             }
            ],
            "tracing": {
             "client_sampling": {
              "value": 100
             },
             "random_sampling": {
              "value": 1
             },
             "overall_sampling": {
              "value": 100
             }
            },
            "server_name": "istio-envoy", /* 设置访问日志格式 */
            "access_log": [
             {
              "name": "envoy.file_access_log",
               ...
             }
            ],
            "use_remote_address": false,
            "generate_request_id": true,
            "forward_client_cert_details": "APPEND_FORWARD",
            "set_current_client_cert_details": {
             "subject": true,
             "dns": true,
             "uri": true
            },
            "upgrade_configs": [
             {
              "upgrade_type": "websocket"
             }
            ],
            "stream_idle_timeout": "0s",
            "normalize_path": true
           }
          }
         ],
         "transport_socket": { /* TLS传输socket配置 */
          "name": "envoy.transport_sockets.tls",
           ...
         },
         "name": "0.0.0.0_80"
        },

Outbound listener: 下面是到Prometheus服务9092端口的outbound listener。10.84.30.227为Prometheus的k8s service地址，指定了后端的cluster outbound|9092||prometheus-k8s.openshift-monitoring.svc.cluster.local。route_config_name字段指定了该listener使用的route prometheus-k8s.openshift-monitoring.svc.cluster.local:9092。

    {
     "name": "10.84.30.227_9092",
     "active_state": {
      "version_info": "2020-09-15T08:05:54Z/4",
      "listener": {
       "@type": "type.googleapis.com/envoy.config.listener.v3.Listener",
       "name": "10.84.30.227_9092",
       "address": {
        "socket_address": {
         "address": "10.84.30.227",
         "port_value": 9092
        }
       },
       "filter_chains": [
        {
         "filters": [
          {
           "name": "istio.stats",
           "typed_config": {
            "@type": "type.googleapis.com/udpa.type.v1.TypedStruct",
            "type_url": "type.googleapis.com/envoy.extensions.filters.network.wasm.v3.Wasm",
            ...
           }
          },
          {
           "name": "envoy.tcp_proxy",/* TCP过滤器设置，设置连接到对应cluster的日志格式 */
           "typed_config": {
            "@type": "type.googleapis.com/envoy.extensions.filters.network.tcp_proxy.v3.TcpProxy",
            "stat_prefix": "outbound|9092||prometheus-k8s.openshift-monitoring.svc.cluster.local",
            "cluster": "outbound|9092||prometheus-k8s.openshift-monitoring.svc.cluster.local",
            "access_log": [
             ...
            ]
           }
          }
         ]
        },
        {
         "filter_chain_match": {
          "application_protocols": [
           "http/1.0",
           "http/1.1",
           "h2c"
          ]
         },
         "filters": [
          {
           "name": "envoy.http_connection_manager", /* 配置HTTP连接 */
           "typed_config": {
            "@type": "type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager",
            "stat_prefix": "outbound_10.84.30.227_9092",
            "rds": { /* RDS接口配置 */
             "config_source": {
              "ads": {},
              "resource_api_version": "V3"
             },
             "route_config_name": "prometheus-k8s.openshift-monitoring.svc.cluster.local:9092" /* 指定路由配置 */
            },
            "http_filters": [
             {
              "name": "istio.metadata_exchange",
              "typed_config": {
               "@type": "type.googleapis.com/udpa.type.v1.TypedStruct",
               "type_url": "type.googleapis.com/envoy.extensions.filters.http.wasm.v3.Wasm",
               ...
              }
             },
             {
              "name": "istio.alpn",
              "typed_config": {
               "@type": "type.googleapis.com/istio.envoy.config.filter.http.alpn.v2alpha1.FilterConfig",
               "alpn_override": [
                {
                 "alpn_override": [
                  "istio-http/1.0",
                  "istio"
                 ]
                },
                {
                 "upstream_protocol": "HTTP11",
                 "alpn_override": [
                  "istio-http/1.1",
                  "istio"
                 ]
                },
                {
                 "upstream_protocol": "HTTP2",
                 "alpn_override": [
                  "istio-h2",
                  "istio"
                 ]
                }
               ]
              }
             },
             {
              "name": "envoy.filters.http.cors",
              "typed_config": {
               "@type": "type.googleapis.com/envoy.extensions.filters.http.cors.v3.Cors"
              }
             },
             {
              "name": "envoy.fault",
              "typed_config": {
               "@type": "type.googleapis.com/envoy.extensions.filters.http.fault.v3.HTTPFault"
              }
             },
             {
              "name": "istio.stats",
              "typed_config": {
               "@type": "type.googleapis.com/udpa.type.v1.TypedStruct",
               "type_url": "type.googleapis.com/envoy.extensions.filters.http.wasm.v3.Wasm",
               ...
              }
             },
             {
              "name": "envoy.router",
              "typed_config": {
               "@type": "type.googleapis.com/envoy.extensions.filters.http.router.v3.Router"
              }
             }
            ],
            "tracing": {
             ...
            },
            "access_log": [
             {
              "name": "envoy.file_access_log",
              ...
              }
             }
            ],
            "use_remote_address": false,
            "generate_request_id": true,
            "upgrade_configs": [
             {
              "upgrade_type": "websocket"
             }
            ],
            "stream_idle_timeout": "0s",
            "normalize_path": true
           }
          }
         ]
        }
       ],
       "deprecated_v1": {
        "bind_to_port": false
       },
       "listener_filters": [
        {
         "name": "envoy.listener.tls_inspector",
         "typed_config": {
          "@type": "type.googleapis.com/envoy.extensions.filters.listener.tls_inspector.v3.TlsInspector"
         }
        },
        {
         "name": "envoy.listener.http_inspector",
         "typed_config": {
          "@type": "type.googleapis.com/envoy.extensions.filters.listener.http_inspector.v3.HttpInspector"
         }
        }
       ],
       "listener_filters_timeout": "5s",
       "traffic_direction": "OUTBOUND",
       "continue_on_listener_filters_timeout": true
      },
      "last_updated": "2020-09-15T08:06:23.989Z"
     }
    },

从上面的配置可以看出，路由配置位于HttpConnectionManager类型中，因此如果某个listener没有用到HTTP，则不会有对应的route。如下面的istiod15012端口上的服务，提供了基于gRPC协议的XDP和CA的服务(使用TLS)。

{
 "name": "10.84.251.157_15012",
 "active_state": {
  "version_info": "2020-09-16T07:48:42Z/22",
  "listener": {
   "@type": "type.googleapis.com/envoy.config.listener.v3.Listener",
   "name": "10.84.251.157_15012",
   "address": {
    "socket_address": {
     "address": "10.84.251.157",
     "port_value": 15012
    }
   },
   "filter_chains": [
    {
     "filters": [
      {
       "name": "istio.stats",
       ...
      },
      {
       "name": "envoy.tcp_proxy",
       "typed_config": {
        "@type": "type.googleapis.com/envoy.extensions.filters.network.tcp_proxy.v3.TcpProxy",
        "stat_prefix": "outbound|15012||istiod.istio-system.svc.cluster.local",
        "cluster": "outbound|15012||istiod.istio-system.svc.cluster.local",
        "access_log": [
         ...
        ]
       }
      }
     ]
    }
   ],
   "deprecated_v1": {
    "bind_to_port": false
   },
   "traffic_direction": "OUTBOUND"
  },
  "last_updated": "2020-09-16T07:49:34.134Z"
 }
},

Route：Istio的route也分为静态配置和动态配置。静态路由配置与静态监听器，以及inbound 动态监听器中设置的静态路由配置(envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager中的route_config)有关。

下面看一个与Prometheus 9092端口提供的服务有关的动态路由，路由配置名称route_config.name与上面Prometheus outbound监听器route_config_name字段指定的值是相同的。

    {
     "version_info": "2020-09-16T07:48:42Z/22",
     "route_config": {
      "@type": "type.googleapis.com/envoy.config.route.v3.RouteConfiguration",
      "name": "prometheus-k8s.openshift-monitoring.svc.cluster.local:9092",
      "virtual_hosts": [
       {
        "name": "prometheus-k8s.openshift-monitoring.svc.cluster.local:9092",
        "domains": [
         "prometheus-k8s.openshift-monitoring.svc.cluster.local",
         "prometheus-k8s.openshift-monitoring.svc.cluster.local:9092",
         "prometheus-k8s.openshift-monitoring",
         "prometheus-k8s.openshift-monitoring:9092",
         "prometheus-k8s.openshift-monitoring.svc.cluster",
         "prometheus-k8s.openshift-monitoring.svc.cluster:9092",
         "prometheus-k8s.openshift-monitoring.svc",
         "prometheus-k8s.openshift-monitoring.svc:9092",
         "10.84.30.227",
         "10.84.30.227:9092"
        ],
        "routes": [
         {
          "match": {
           "prefix": "/"
          },
          "route": { /* 路由到的后端cluster */
           "cluster": "outbound|9092||prometheus-k8s.openshift-monitoring.svc.cluster.local",
           "timeout": "0s",
           "retry_policy": {
            "retry_on": "connect-failure,refused-stream,unavailable,cancelled,retriable-status-codes",
            "num_retries": 2,
            "retry_host_predicate": [
             {
              "name": "envoy.retry_host_predicates.previous_hosts"
             }
            ],
            "host_selection_retry_max_attempts": "5",
            "retriable_status_codes": [
             503
            ]
           },
           "max_grpc_timeout": "0s"
          },
          "decorator": {
           "operation": "prometheus-k8s.openshift-monitoring.svc.cluster.local:9092/*"
          },
          "name": "default"
         }
        ],
        "include_request_attempt_count": true
       }
      ],
      "validate_clusters": false
     },
     "last_updated": "2020-09-16T07:49:52.551Z"
    },

更多内容可以参考Envoy的官方文档

下面是基于Istio官方BookInfo的一个访问流程图，可以帮助理解整个流程。

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