注：以下讲述的按理环境场景是基于Kubernetes环境基础上部署的Istio环境。

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涉及到Envoy概念介绍请参考深度解析Istio系列之流量控制篇。本文重点针对Envoy初始化场景进行拆解。

Istio-proxy（Envoy）作为Istio数据平面的重要组件，基于sidecar方式与业务应用混合部署到同一pod，为应用提供代理服务。Pilot作为控制平面组件，基于元数据的抽象层，屏蔽底层具体容器环境（Kubernetes或者docker），同时为Envoy的策略执行提供有效的数据支撑。那么Envoy如何获取Pilot所在地址的信息呢？

下面通过官网BookInfo案例中Productpage服务的配置文件来说明。

Pod容器说明

执行kubectl get deploy productpage-v1 -o yaml，获取productpage部署模板，如下所示：

apiVersion: extensions/v1beta1

kind: Deployment

metadata:

  annotations:

    deployment.kubernetes.io/revision: "2"

    kubectl.kubernetes.io/last-applied-configuration: |

{"apiVersion":"extensions/v1beta1","kind":"Deployment","metadata":{"annotations":{},"creationTimestamp":null,"name":"productpage-v1","namespace":"default"},"spec":{"replicas":1,"strategy":{},"template":{"metadata":{"annotations":{"sidecar.istio.io/status":"{\"version\":\"50128f63e7b050c58e1cdce95b577358054109ad2aff4bc4995158c06924a43b\",\"initContainers\":[\"istio-init\"],\"containers\":[\"istio-proxy\"],\"volumes\":[\"istio-envoy\",\"istio-certs\"],\"imagePullSecrets\":null}"},"creationTimestamp":null,"labels":{"app":"productpage","version":"v1"}},"spec":{"containers":[{"image":"istio/examples-bookinfo-productpage-v1:1.8.0","imagePullPolicy":"IfNotPresent","name":"productpage","ports":[{"containerPort":9080}],"resources":{}},{"args":["proxy","sidecar","--configPath","/etc/istio/proxy","--binaryPath","/usr/local/bin/envoy","--serviceCluster","productpage","--drainDuration","45s","--parentShutdownDuration","1m0s","--discoveryAddress","istio-pilot.istio-system:15007","--discoveryRefreshDelay","1s","--zipkinAddress","zipkin.istio-system:9411","--connectTimeout","10s","--proxyAdminPort","15000","--controlPlaneAuthPolicy","NONE"],"env":[{"name":"POD_NAME","valueFrom":{"fieldRef":{"fieldPath":"metadata.name"}}},{"name":"POD_NAMESPACE","valueFrom":{"fieldRef":{"fieldPath":"metadata.namespace"}}},{"name":"INSTANCE_IP","valueFrom":{"fieldRef":{"fieldPath":"status.podIP"}}},{"name":"ISTIO_META_POD_NAME","valueFrom":{"fieldRef":{"fieldPath":"metadata.name"}}},{"name":"ISTIO_META_INTERCEPTION_MODE","value":"REDIRECT"},{"name":"ISTIO_METAJSON_LABELS","value":"{\"app\":\"productpage\",\"version\":\"v1\"}\n"}],"image":"docker.io/istio/proxyv2:1.0.5","imagePullPolicy":"IfNotPresent","name":"istio-proxy","ports":[{"containerPort":15090,"name":"http-envoy-prom","protocol":"TCP"}],"resources":{"requests":{"cpu":"10m"}},"securityContext":{"readOnlyRootFilesystem":true,"runAsUser":1337},"volumeMounts":[{"mountPath":"/etc/istio/proxy","name":"istio-envoy"},{"mountPath":"/etc/certs/","name":"istio-certs","readOnly":true}]}],"initContainers":[{"args":["-p","15001","-u","1337","-m","REDIRECT","-i","*","-x","","-b","9080","-d",""],"image":"docker.io/istio/proxy_init:1.0.5","imagePullPolicy":"IfNotPresent","name":"istio-init","resources":{},"securityContext":{"capabilities":{"add":["NET_ADMIN"]},"privileged":true}}],"volumes":[{"emptyDir":{"medium":"Memory"},"name":"istio-envoy"},{"name":"istio-certs","secret":{"optional":true,"secretName":"istio.default"}}]}}},"status":{}}

  creationTimestamp: 2018-12-18T01:51:18Z

  generation: 2

  labels:

    app: productpage

    version: v1

  name: productpage-v1

  namespace: default

  resourceVersion: "17402700"

  selfLink: /apis/extensions/v1beta1/namespaces/default/deployments/productpage-v1

  uid: 695ba22c-0267-11e9-8475-0050569c62d0

spec:

  progressDeadlineSeconds: 600

  replicas: 1

  revisionHistoryLimit: 10

  selector:

    matchLabels:

      app: productpage

      version: v1

  strategy:

    rollingUpdate:

      maxSurge: 1

      maxUnavailable: 1

    type: RollingUpdate

  template:

    metadata:

      annotations:

        sidecar.istio.io/status: '{"version":"50128f63e7b050c58e1cdce95b577358054109ad2aff4bc4995158c06924a43b","initContainers":["istio-init"],"containers":["istio-proxy"],"volumes":["istio-envoy","istio-certs"],"imagePullSecrets":null}'

      creationTimestamp: null

      labels:

        app: productpage

        version: v1

    spec:

      containers:

      - image: istio/examples-bookinfo-productpage-v1:1.8.0

        imagePullPolicy: IfNotPresent

        name: productpage

        ports:

        - containerPort: 9080

          protocol: TCP

        resources: {}

        terminationMessagePath: /dev/termination-log

        terminationMessagePolicy: File

      - args:

        - proxy

        - sidecar

        - --configPath

        - /etc/istio/proxy

        - --binaryPath

        - /usr/local/bin/envoy

        - --serviceCluster

        - productpage

        - --drainDuration

        - 45s

        - --parentShutdownDuration

        - 1m0s

        - --discoveryAddress

        - istio-pilot.istio-system:15007

        - --discoveryRefreshDelay

        - 1s

        - --zipkinAddress

        - zipkin.istio-system:9411

        - --connectTimeout

        - 10s

        - --proxyAdminPort

        - "15000"

        - --controlPlaneAuthPolicy

        - NONE

        env:

        - name: POD_NAME

          valueFrom:

            fieldRef:

              apiVersion: v1

              fieldPath: metadata.name

        - name: POD_NAMESPACE

          valueFrom:

            fieldRef:

              apiVersion: v1

              fieldPath: metadata.namespace

        - name: INSTANCE_IP

          valueFrom:

            fieldRef:

              apiVersion: v1

              fieldPath: status.podIP

        - name: ISTIO_META_POD_NAME

          valueFrom:

            fieldRef:

              apiVersion: v1

              fieldPath: metadata.name

        - name: ISTIO_META_INTERCEPTION_MODE

          value: REDIRECT

        - name: ISTIO_METAJSON_LABELS

          value: |

            {"app":"productpage","version":"v1"}

        image: docker.io/istio/proxyv2:1.0.5

        imagePullPolicy: IfNotPresent

        name: istio-proxy

        ports:

        - containerPort: 15090

          name: http-envoy-prom

          protocol: TCP

        resources:

          requests:

            cpu: 10m

        securityContext:

          readOnlyRootFilesystem: true

          runAsUser: 1337

        terminationMessagePath: /dev/termination-log

        terminationMessagePolicy: File

        volumeMounts:

        - mountPath: /etc/istio/proxy

          name: istio-envoy

        - mountPath: /etc/certs/

          name: istio-certs

          readOnly: true

      DNSPolicy: ClusterFirst

      initContainers:

      - args:

        - -p

        - "15001"

        - -u

        - "1337"

        - -m

        - REDIRECT

        - -i

        - '*'

        - -x

        - ""

        - -b

        - "9080"

        - -d

        - ""

        image: docker.io/istio/proxy_init:1.0.5

        imagePullPolicy: IfNotPresent

        name: istio-init

        resources: {}

        securityContext:

          capabilities:

            add:

            - NET_ADMIN

          privileged: true

        terminationMessagePath: /dev/termination-log

        terminationMessagePolicy: File

      restartPolicy: Always

      schedulerName: default-scheduler

      securityContext: {}

      terminationGracePeriodSeconds: 30

      volumes:

      - emptyDir:

          medium: Memory

        name: istio-envoy

      - name: istio-certs

        secret:

          defaultMode: 420

          optional: true

          secretName: istio.default

status:

  availableReplicas: 1

  conditions:

  - lastTransitionTime: 2018-12-18T01:51:19Z

    lastUpdateTime: 2018-12-18T01:51:19Z

    message: Deployment has minimum availability.

    reason: MinimumReplicasAvailable

    status: "True"

    type: Available

  - lastTransitionTime: 2018-12-18T01:51:18Z

    lastUpdateTime: 2018-12-18T03:48:52Z

    message: ReplicaSet "productpage-v1-7b96bbf89f" has successfully progressed.

    reason: NewReplicaSetAvailable

    status: "True"

    type: Progressing

  observedGeneration: 2

  readyReplicas: 1

  replicas: 1

  updatedReplicas: 1

模板中可见，除业务应用外，还包括istio-init，istio-proxy两个容器。istio-init作为Init Container类型，在应用容器启动之前启动，用来执行初始化任务。Istio-init主要初始化iptables规则，用于服务间调用时的请求拦截及转发。Istio-proxy是代理容器（即Envoy），容器中包含两个进程，分别是Pilot-agent进程和Envoy进程。前者负责生成Envoy启动所需的配置文件，启动Envoy进程。后者在服务调用发生时负责具体的策略执行。

Envoy配置信息详解

Envoy启动后，执行kubectl exec -it productpage-v1-7b96bbf89f-pj28l -c istio-proxy /bin/sh，进入istio-proxy容器内部，在/etc/istio/proxy目录下存在envoy-rev0.json配置文件，如图2所示：

该文件是Pilot是Pilot-agent进程根据服务启动参数以及Kubernetes Server API的信息生成，配置文件框架如图3所示：

Node包含的信息如图4所示：

这里重点说明cluster属性，该属性值为productpage，说明当前的istio-proxy服务为productpage应用的代理服务，iptables将调用productpage服务请求拦截后，直接转发到该istio-proxy进行处理。

stats_config包含的信息如图5所示：

static_config重点设定部分属性的命名规则。

admin包含的信息如图6所示：

admin类似Envoy内部的一个管理器，暴露出的15000端口只能在容器内部被访问。

通过curl http://127.0.0.1:15000/help访问能获取其他接口信息，如下图7所示：

dynamic_resources包含的信息如图8所示：

dynamic_resources中记录pilot调取XDS接口采用ADS聚合发现服务，这种方式能更好的保证从pilot上获取到的数据的一致性。

static_resources包含的部分信息如图9所示：

static_resources name属性值为xds-grpc，与上述dynamic_resources模块的信息里cluster_name的值一致。同时xds-grpc对象信息中包括pilot组件的服务地址“istio-pilot.istio-system:15010”，即为istio-proxy从pilot获取动态信息的服务地址。Istio-proxy（Envoy）通过该地址调取XDS接口，获取服务信息。除此之外，static_resources中提供zipkin服务的地址，zipkin是用于服务分布式跟踪。

综上可知Envoy启动时，pilot-agent进程生成Envoy启动所需的配置文件，Envoy基于配置文件中携带的pilot地址信息动态获取服务信息，并且基于pilot提供的XDS接口，动态获取服务的listener，cluster，endpoint和route信息。

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