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。
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Env oy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。
