connect Postgres database in docker to app in Kubernetes

Question

I'm new with Kubernetes and I try to understand how to connect Postgres database which is outside from Kubernetes (exactly in docker with ip address 172.17.0.2 and port 5432) to my webapp in Kubernetes.

I try connect database through env variable PS_DATABASE_URL in Deployment section.

But it cannot find mentioned url for postgres. How it need to be done correctly?

webapp.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp-deployment
  labels:
    app: webapp
spec:
  replicas: 1
  selector:
    matchLabels:
      app: webapp
  template:
    metadata:
      labels:
        app: webapp
    spec:
      containers:
      - name: webapp
        image: dmitriy83/flask_kuber
        ports:
        - containerPort: 5000
        env:
          - name: PS_DATABASE_URL
            value: postgresql://postgres:[email protected]:5432/db
---
apiVersion: v1
kind: Service
metadata:
  name: webapp-service
spec:
  type: NodePort
  selector:
    app: webapp
  ports:
    - protocol: TCP
      port: 5000
      targetPort: 5000
      nodePort: 30100

Hey Dmitriy, where your k8s infra is hosted? Minikube, cloud? — jabbson
– jabbson, Commented Dec 3, 2021 at 17:49
Can you move the database into Kubernetes too? If not, "in Docker" isn't really a meaningful place for the database to be running; the Kubernetes cluster would probably need to connect to a published port on the host running the container, the same as any other out-of-cluster resource. — David Maze
– David Maze, Commented Dec 3, 2021 at 19:25
can you check is the k8s master has the connectivity of ip and port of database, there might be some firewall issue — Hackaholic
– Hackaholic, Commented Dec 3, 2021 at 21:39
@DavidMaze i understand that Docker not the best place for db. Ii need to know how to connect external db which is not in Kubernetes to app in Kubernetes — Dmitriy_kzn
– Dmitriy_kzn, Commented Dec 4, 2021 at 4:18

Dmitriy_kzn · Accepted Answer · 2021-12-10 08:14:07Z

I figured it out. it depends from cloud provider. For this example i use amazon cloud and to connect database on amazon (this is external service). So we must define it in yaml file like an external service.

postgres_external.yaml

kind: Service
apiVersion: v1
metadata:
  name: postgres
spec:
  type: ExternalName
  externalName: db.cdmhjidhpqyu.us-east-2.rds.amazonaws.com

to connect to external service you need to link to it on deployment.

webapp.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp-deployment
  labels:
    app: webapp
spec:
  replicas: 1
  selector:
    matchLabels:
      app: webapp
  template:
    metadata:
      labels:
        app: webapp
    spec:
      containers:
      - name: webapp
        image: dmitriy83/flask_kuber
        ports:
        - containerPort: 5000
        env:
          - name: PS_DATABASE_URL
            value: postgresql://<username>:<password>@postgres:5432/db
---
apiVersion: v1
kind: Service
metadata:
  name: webapp-service
spec:
  type: NodePort
  selector:
    app: webapp
  ports:
    - protocol: TCP
      port: 5000
      targetPort: 5000
      nodePort: 30100

Please note in webapp.yaml, env section value value: postgresql://<username>:<password>@postgres:5432/db contains postgres - this is name of our external service which we define in postgres_external.yaml

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