注：以下講述的按理環境場景是基於Kubernetes環境基礎上部署的Istio環境。
涉及到Envoy概念介紹請參考深度解析Istio系列之流量控制篇。本文重點針對Envoy初始化場景進行拆解。
Istio-proxy（Envoy）作爲Istio數據平面的重要組件，基於sidecar方式與業務應用混合部署到同一pod，爲應用提供代理服務。Pilot作爲控制平面組件，基於元數據的抽象層，屏蔽底層具體容器環境（Kubernetes或者docker），同時爲Envoy的策略執行提供有效的數據支撐。那麼Envoy如何獲取Pilot所在地址的信息呢？
下面通過官網BookInfo案例中Productpage服務的配置文件來說明。
Pod容器說明
執行kubectl get deploy productpage-v1 -o yaml，獲取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
模板中可見，除業務應用外，還包括istio-init，istio-proxy兩個容器。istio-init作爲Init Container類型，在應用容器啓動之前啓動，用來執行初始化任務。Istio-init主要初始化iptables規則，用於服務間調用時的請求攔截及轉發。Istio-proxy是代理容器（即Envoy），容器中包含兩個進程，分別是Pilot-agent進程和Envoy進程。前者負責生成Envoy啓動所需的配置文件，啓動Envoy進程。後者在服務調用發生時負責具體的策略執行。
Envoy配置信息詳解
Envoy啓動後，執行kubectl exec -it productpage-v1-7b96bbf89f-pj28l -c istio-proxy /bin/sh，進入istio-proxy容器內部，在/etc/istio/proxy目錄下存在envoy-rev0.json配置文件，如圖2所示：
該文件是Pilot是Pilot-agent進程根據服務啓動參數以及Kubernetes Server API的信息生成，配置文件框架如圖3所示：
Node包含的信息如圖4所示：
這裏重點說明cluster屬性，該屬性值爲productpage，說明當前的istio-proxy服務爲productpage應用的代理服務，iptables將調用productpage服務請求攔截後，直接轉發到該istio-proxy進行處理。
stats_config包含的信息如圖5所示：
static_config重點設定部分屬性的命名規則。
admin包含的信息如圖6所示：
admin類似Envoy內部的一個管理器，暴露出的15000端口只能在容器內部被訪問。
通過curl http://127.0.0.1:15000/help訪問能獲取其他接口信息，如下圖7所示：
dynamic_resources包含的信息如圖8所示：
dynamic_resources中記錄pilot調取XDS接口採用ADS聚合發現服務，這種方式能更好的保證從pilot上獲取到的數據的一致性。
static_resources包含的部分信息如圖9所示：
static_resources name屬性值爲xds-grpc，與上述dynamic_resources模塊的信息裏cluster_name的值一致。同時xds-grpc對象信息中包括pilot組件的服務地址“istio-pilot.istio-system:15010”，即爲istio-proxy從pilot獲取動態信息的服務地址。Istio-proxy（Envoy）通過該地址調取XDS接口，獲取服務信息。除此之外，static_resources中提供zipkin服務的地址，zipkin是用於服務分佈式跟蹤。
綜上可知Envoy啓動時，pilot-agent進程生成Envoy啓動所需的配置文件，Envoy基於配置文件中攜帶的pilot地址信息動態獲取服務信息，並且基於pilot提供的XDS接口，動態獲取服務的listener，cluster，endpoint和route信息。
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