Docker Kubernetes and Name Reslution-CodePudding

I am running Docker Desktop on Windows 10

I have Docket Kubernetes enabled
In my Kubernetes cluster I have a single pod with a single container running Postgres, built with kubectl apply (call this inside)
Outside of Kubernetes, I have another container running postgres built with docker desktop (call this outside).

I want to be able to connect to the outside postgres server by name from the inside to the outside

My kubernetes yaml configuration that builds inside:

apiVersion: v1
kind: PersistentVolume # Create a PV
metadata:
  name: postgresql-data # Sets PV's name
  labels:
    type: local # Sets PV's type to local
spec:
  storageClassName: manual
  capacity:
    storage: 10Gi # Sets PV Volume
  accessModes:
    - ReadWriteOnce
  hostPath: #/run/desktop/mnt/host/c points to c:\ on the windows host
    path: "/run/desktop/mnt/host/c/mk/data/volume" # Sets the volume's path
---
apiVersion: v1
kind: PersistentVolumeClaim # Create PVC
metadata:
  name: postgresql-data-claim # Sets name of PV
spec:
  storageClassName: manual
  accessModes:
    - ReadWriteOnce # Sets read and write access
  resources:
    requests:
      storage: 10Gi # Sets volume size    
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: postgres-secret
  labels:
    app: postgres
data:
  POSTGRES_DB: appdb
  POSTGRES_USER: user
  POSTGRES_PASSWORD: password
---
apiVersion: apps/v1
kind: Deployment # Create a deployment
metadata:
  name: postgres # Set the name of the deployment
spec:
  replicas: 1 
  selector:
    matchLabels:
      app: postgres
  template:
    metadata:
      labels:
        app: postgres
    spec:
      containers:
        - name: postgres
          image: postgres:12.10 # Docker image
          imagePullPolicy: "IfNotPresent"
          ports:
            - containerPort: 5432 # Exposing the container port 5432 for PostgreSQL client connections.
          envFrom:
            - configMapRef:
                name: postgres-secret # Using the ConfigMap postgres-secret
          volumeMounts:
            - mountPath: /var/lib/postgresql/data
              name: postgresdata
      volumes:
        - name: postgresdata
          persistentVolumeClaim:
            claimName: postgresql-data-claim
---
apiVersion: v1
kind: Service # Create service
metadata:
  name: postgres # Sets the service name
  labels:
    app: postgres # Defines app to create service for
spec:
  type: NodePort # Sets the service type
  ports:
    - protocol: TCP # Sets the port to run the postgres application
      port: 5432
      targetPort: 5432
      nodePort: 31225
  selector:
    app: postgres

My docker-compose that builds outside

version: '3.6'
services:
  client_portal:
    image: postgres:13.3
    ports: 
      - 5435:5432
    environment:
      POSTGRES_PASSWORD: appdb
      POSTGRES_USER: user
      POSTGRES_DB: password

From the windows host, I am able to access inside at localhost:5432. Outside is accessed at localhost:31225

From inside I can access outside by it's ip address. I got the ip address by running hostname -i on outside`'s console (172.18.0.3) .

This works (on inside):

psql postgresql://user:[email protected]:5432/appdb

I want to address it by name (not ip) so that when I share this with someone else or the ip address of outside changes, my config does not change.

CodePudding user response：

You can check the node object in your cluster to see what is the hostname for this node. It should probably be docker-desktop. You can check this as:

kubectl get node docker-desktop -oyaml

This should provide an output similar to the following:

...
status:
    addresses:
    - address: 192.168.65.4
      type: InternalIP
    - address: docker-desktop
      type: Hostname
...

I believe in your case the InternalIP address is 172.18.0.3. It is the one you can use to address the node from inside the cluster.

Assuming that when you provide this setup to someone else, and they will also use docker desktop, the hostname should be docker-desktop.

You can simply use the following command from inside, safely:

psql postgresql://user:password@docker-desktop:5432/appdb

Just make sure docker-desktop is the hostname for the node, as checked earlier.