Istio流量管理--Ingress Gateway

传统上，Kubernetes使用Ingress控制器来处理从外部进入集群的流量。使用Istio时，情况不再如此。 Istio已用新的Gateway和VirtualServices资源替换了熟悉的Ingress资源。它们协同工作，将流量路由到网格中。在网格内部，不需要Gateway，因为服务可以通过集群本地服务名称相互访问。

正如我之前文章介绍过的，kubernetes提供的Ingress过于简单，暴露出来的属性表达性太弱。当然社区也意识到了这个问题，从kubernetes1.19 版本，在逐步补全功能。Istio解决方案中，自己实现了Istio gateway。在非istio场景外，gloo，ambasaador ，contour等网关 可以满足我们生产环境的需求。

部署

我们看下社区默认的部署。

通过Deployment管理的一组istio-ingressgateway Pod。

IngressGateway，这是Envoy代理的封装。它的配置方式与服务网格中使用的Sidecar相同。当我们创建或更改Gateway或VirtualService时，Istio Pilot控制器会检测到更改，该控制器会将这些信息转换为Envoy配置并将其发送到相关代理，包括IngressGateway内部的Envoy。

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: istio-ingressgateway
    istio: ingressgateway
    release: istio
  name: istio-ingressgateway
  namespace: istio-system
spec:
  selector:
    matchLabels:
      app: istio-ingressgateway
      istio: ingressgateway
  strategy:
    rollingUpdate:
      maxSurge: 100%
      maxUnavailable: 25%
  template:
    metadata:
      annotations:
        prometheus.io/path: /stats/prometheus
        prometheus.io/port: "15090"
        prometheus.io/scrape: "true"
        sidecar.istio.io/inject: "false"
      labels:
        app: istio-ingressgateway
        chart: gateways
        heritage: Tiller
        istio: ingressgateway
        release: istio
        service.istio.io/canonical-name: istio-ingressgateway
        service.istio.io/canonical-revision: latest
    spec:
      affinity:
        nodeAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
          - preference:
              matchExpressions:
              - key: kubernetes.io/arch
                operator: In
                values:
                - amd64
            weight: 2
          - preference:
              matchExpressions:
              - key: kubernetes.io/arch
                operator: In
                values:
                - ppc64le
            weight: 2
          - preference:
              matchExpressions:
              - key: kubernetes.io/arch
                operator: In
                values:
                - s390x
            weight: 2
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key: kubernetes.io/arch
                operator: In
                values:
                - amd64
                - ppc64le
                - s390x
      containers:
      - args:
        - proxy
        - router
        - --domain
        - $(POD_NAMESPACE).svc.cluster.local
        - --proxyLogLevel=warning
        - --proxyComponentLogLevel=misc:error
        - --log_output_level=default:info
        - --serviceCluster
        - istio-ingressgateway
        - --trust-domain=cluster.local
        env:
        - name: JWT_POLICY
          value: third-party-jwt
        - name: PILOT_CERT_PROVIDER
          value: istiod
        - name: CA_ADDR
          value: istiod.istio-system.svc:15012
        - name: NODE_NAME
          valueFrom:
            fieldRef:
              apiVersion: v1
              fieldPath: spec.nodeName
        - 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: HOST_IP
          valueFrom:
            fieldRef:
              apiVersion: v1
              fieldPath: status.hostIP
        - name: SERVICE_ACCOUNT
          valueFrom:
            fieldRef:
              fieldPath: spec.serviceAccountName
        - name: CANONICAL_SERVICE
          valueFrom:
            fieldRef:
              fieldPath: metadata.labels['service.istio.io/canonical-name']
        - name: CANONICAL_REVISION
          valueFrom:
            fieldRef:
              fieldPath: metadata.labels['service.istio.io/canonical-revision']
        - name: ISTIO_META_WORKLOAD_NAME
          value: istio-ingressgateway
        - name: ISTIO_META_OWNER
          value: kubernetes://apis/apps/v1/namespaces/istio-system/deployments/istio-ingressgateway
        - name: ISTIO_META_MESH_ID
          value: cluster.local
        - name: ISTIO_META_ROUTER_MODE
          value: sni-dnat
        - name: ISTIO_META_CLUSTER_ID
          value: Kubernetes
        image: docker.io/istio/proxyv2:1.7.3
        name: istio-proxy
        ports:
        - containerPort: 15021
        - containerPort: 8080
        - containerPort: 8443
        - containerPort: 15443
        - containerPort: 15090
          name: http-envoy-prom
          protocol: TCP
        readinessProbe:
          failureThreshold: 30
          httpGet:
            path: /healthz/ready
            port: 15021
            scheme: HTTP
          initialDelaySeconds: 1
          periodSeconds: 2
          successThreshold: 1
          timeoutSeconds: 1
        resources:
          limits:
            cpu: 2000m
            memory: 1024Mi
          requests:
            cpu: 100m
            memory: 128Mi
        securityContext:
          allowPrivilegeEscalation: false
          capabilities:
            drop:
            - ALL
          privileged: false
          readOnlyRootFilesystem: true
        volumeMounts:
        - mountPath: /etc/istio/proxy
          name: istio-envoy
        - mountPath: /etc/istio/config
          name: config-volume
        - mountPath: /var/run/secrets/istio
          name: istiod-ca-cert
        - mountPath: /var/run/secrets/tokens
          name: istio-token
          readOnly: true
        - mountPath: /var/run/ingress_gateway
          name: gatewaysdsudspath
        - mountPath: /etc/istio/pod
          name: podinfo
        - mountPath: /etc/istio/ingressgateway-certs
          name: ingressgateway-certs
          readOnly: true
        - mountPath: /etc/istio/ingressgateway-ca-certs
          name: ingressgateway-ca-certs
          readOnly: true
      securityContext:
        fsGroup: 1337
        runAsGroup: 1337
        runAsNonRoot: true
        runAsUser: 1337
      serviceAccountName: istio-ingressgateway-service-account
      volumes:
      - configMap:
          name: istio-ca-root-cert
        name: istiod-ca-cert
      - downwardAPI:
          items:
          - fieldRef:
              fieldPath: metadata.labels
            path: labels
          - fieldRef:
              fieldPath: metadata.annotations
            path: annotations
        name: podinfo
      - emptyDir: {}
        name: istio-envoy
      - emptyDir: {}
        name: gatewaysdsudspath
      - name: istio-token
        projected:
          sources:
          - serviceAccountToken:
              audience: istio-ca
              expirationSeconds: 43200
              path: istio-token
      - configMap:
          name: istio
          optional: true
        name: config-volume
      - name: ingressgateway-certs
        secret:
          optional: true
          secretName: istio-ingressgateway-certs
      - name: ingressgateway-ca-certs
        secret:
          optional: true
          secretName: istio-ingressgateway-ca-certs

我们在IngressGateway部署中必须关心的是SSL证书。为了能够访问gateway资源中的证书，请确保已正确安装了证书。

 volumeMounts:
        - mountPath: /etc/istio/ingressgateway-certs
          name: ingressgateway-certs
          readOnly: true
        - mountPath: /etc/istio/ingressgateway-ca-certs
          name: ingressgateway-ca-certs
          readOnly: true
     
      volumes:
      - name: ingressgateway-certs
        secret:
          optional: true
          secretName: istio-ingressgateway-certs
      - name: ingressgateway-ca-certs
        secret:
          optional: true
          secretName: istio-ingressgateway-ca-certs 

由于istio-ingressgateway 主要处理边界流量，所以必须创建LoadBalancer类型的service，所有外部流量都通过此云负载均衡器进入集群，该负载均衡器将流量路由到istio-ingressgateway的envoy容器。

apiVersion: v1
kind: Service
metadata:
  labels:
    app: istio-ingressgateway
    istio: ingressgateway
    release: istio
  name: istio-ingressgateway
  namespace: istio-system
spec:
  ports:
  - name: status-port
    port: 15021
    targetPort: 15021
  - name: http2
    port: 80
    targetPort: 8080
  - name: https
    port: 443
    targetPort: 8443
  - name: tls
    port: 15443
    targetPort: 15443
  selector:
    app: istio-ingressgateway
    istio: ingressgateway
  type: LoadBalancer

出于性能考虑，我们应该讲.spec.externalTrafficPolicy设置为local模式，避免二跳。

其他包括HPA，PDB以及RBAC等资源。

单集群多Gateway

有时创建多个ingress gateway也很有用。例如，在一个非常大的集群中，有成千上万的服务，您可能不想通过一个云负载均衡器和一个部署来驱动所有外部流量，但希望水平分担负载。

部署多个Gateway，比较简单，参照上一步部署，注意更改一下命名，复制多个部署即可。

那我们如何选择ingress gateway那？通过selector选择。如下：

metadata:
  name: gateway
spec:
  selector:
    istio: second-istio-ingressgateway

配置

Ingress Gateway 不包含任何流量路由配置。Ingress 流量的路由使用 Istio 路由规则来配置，和内部服务请求完全一样。

让我们一起来看如何为 HTTP 流量在 80 端口上配置 Gateway。

1. 创建 Istio Gateway：

$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: httpbin-gateway
spec:
  selector:
    istio: ingressgateway # use Istio default gateway implementation
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - "httpbin.example.com"
EOF

1. 为通过 Gateway 的入口流量配置路由：

$ kubectl apply -f - <<EOF
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: httpbin
spec:
  hosts:
  - "httpbin.example.com"
  gateways:
  - httpbin-gateway
  http:
  - match:
    - uri:
        prefix: /status
    - uri:
        prefix: /delay
    route:
    - destination:
        port:
          number: 8000
        host: httpbin
EOF

已为 httpbin 服务创建了虚拟服务配置，包含两个路由规则，允许流量流向路径 /status 和 /delay。

gateways 列表规约了哪些请求允许通过 httpbin-gateway 网关。 所有其他外部请求均被拒绝并返回 404 响应。

安全性

使用 SDS 为 Gateway 提供 HTTPS 加密支持

可以配置 TLS Ingress Gateway ，让它从 Ingress Gateway 代理通过 SDS 获取凭据。Ingress Gateway 代理和 Ingress Gateway 在同一个 Pod 中运行，监视 Ingress Gateway 所在命名空间中新建的 Secret。在 Ingress Gateway 中启用 SDS 具有如下好处：

• Ingress Gateway 无需重启，就可以动态的新增、删除或者更新密钥/证书对以及根证书。
• 无需加载 Secret 卷。创建了 kubernetes`Secret 之后，这个 Secret` 就会被 Gateway 代理捕获，并以密钥/证书对和根证书的形式发送给 Ingress Gateway 。
• Gateway 代理能够监视多个密钥/证书对。只需要为每个主机名创建 Secret 并更新 Gateway 定义就可以了。

无 TLS 终止的 Ingress Gateway

配置 Ingress Gateway 以执行 SNI 透传，而不是对传入请求进行 TLS 终止。例如：

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: mygateway
spec:
  selector:
    istio: ingressgateway # use istio default ingress gateway
  servers:
  - port:
      number: 443
      name: https
      protocol: HTTPS
    tls:
      mode: PASSTHROUGH
    hosts:
    - nginx.example.com