Number of connections opened to gRPC server

Networking
1

Hi all,

Istio Proxy: 1.15.3

I am trying to figure out how number of opened connections/sockets between gRPC client and server is determined in Istio mesh.

The following client will open 8 connections, I guess this is driven by concurrency parameter as per source code: istio/inject.go at 1.15.3 · istio/istio · GitHub, however server can only see one connection. I tried setting different concurrency and cpu hoping it would increase number of server connections, however the results were never deterministic. For completeness, I included Virtual Service and Destination Rule.

Client:

apiVersion: batch/v1
kind: Job
metadata:
  annotations:
  name: client
spec:
  template:
    metadata:
      annotations:
        proxy.istio.io/config: '{ "holdApplicationUntilProxyStarts": true, "concurrency": 8 }'
        sidecar.istio.io/inject: "true"
        sidecar.istio.io/proxyCPU: "4"
        sidecar.istio.io/proxyCPULimit: "4"
        sidecar.istio.io/proxyMemory: 1Gi
        sidecar.istio.io/proxyMemoryLimit: 1Gi
    spec:
      containers:
      - image: dummy:latest
        imagePullPolicy: IfNotPresent
        name: dummy
        resources:
          limits:
            cpu: "4"
            memory: 4Gi
          requests:
            cpu: "4"
            memory: 4Gi

Server:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: server
spec:
  replicas: 1
  selector:
    matchLabels:
      app: server
  strategy:
    rollingUpdate:
      maxSurge: 5%
      maxUnavailable: 100%
    type: RollingUpdate
  template:
    metadata:
      annotations:
        proxy.istio.io/config: '{ "holdApplicationUntilProxyStarts": true }'
        sidecar.istio.io/inject: "true"
    spec:
      containers:
      - image: server:latest
        imagePullPolicy: IfNotPresent
        livenessProbe:
          exec:
            command:
            - /bin/grpc_health_probe
            - -addr=:9999
            - -service=liveness
          failureThreshold: 3
          initialDelaySeconds: 60
          periodSeconds: 60
          successThreshold: 1
          timeoutSeconds: 20
        name: server
        readinessProbe:
          exec:
            command:
            - /bin/grpc_health_probe
            - -addr=:9999
          failureThreshold: 5
          initialDelaySeconds: 3
          periodSeconds: 10
          successThreshold: 1
          timeoutSeconds: 1
        resources:
          limits:
            cpu: "3"
            memory: 2Gi
          requests:
            cpu: "3"
            memory: 2Gi

apiVersion: networking.istio.io/v1beta1
kind: VirtualService
metadata:
  name: server
spec:
  hosts:
  - server
  http:
  - name: server
    route:
    - destination:
        host: server
        port:
          number: 9999
      headers:
        request:
          remove:
          - grpc-accept-encoding

apiVersion: networking.istio.io/v1beta1
kind: DestinationRule
metadata:
  name: server
spec:
  host: server
  trafficPolicy:
    loadBalancer:
      simple: LEAST_REQUEST

apiVersion: v1
kind: Service
metadata:
  name: server
spec:
  ports:
  - name: grpc
    port: 9999
    protocol: TCP
    targetPort: grpc
  selector:
    app: server