Kubernetes (in Docker for Windows) Volume Configuration for Postgres

Question

I have a tomcat + postgres application that I test with docker-compose. I am trying to package the application in a kubernetes config file.

For now, I am running kubernetes (and kubectl) using my Docker Desktop for Windows installation. Eventually, I want to deploy to other environments.

I am currently trying to replicate some of the volume functionality in docker-compose within the following config file.

apiVersion: v1
kind: Pod
metadata:
  name: pg-pod
spec:
  volumes:
  - name: "pgdata-vol"
    #emptyDir: {}
    hostPath:
      path: /c/temp/vols/pgdata
  containers:
  - image: postgres
    name: db
    ports:
    - containerPort: 5432
      name: http
      protocol: TCP
    volumeMounts:
    - mountPath: "/pgdata"
      name: "pgdata-vol"
    env:
    - name: PGDATA
      value: /pgdata

When postgres launches, I get see the following error.

fixing permissions on existing directory /pgdata ... ok
creating subdirectories ... ok
selecting default max_connections ... 20
selecting default shared_buffers ... 400kB
selecting dynamic shared memory implementation ... posix
creating configuration files ... ok
2019-07-26 20:43:41.844 UTC [78] FATAL:  data directory "/pgdata" has wrong ownership
2019-07-26 20:43:41.844 UTC [78] HINT:  The server must be started by the user that owns the data directory.
child process exited with exit code 1
initdb: removing contents of data directory "/pgdata"
running bootstrap script ...

I presume that I either need to provide some additional parameters to my volume definition or I need to try a different type of volume config (local vs hostPath).

terrywb · Accepted Answer · 2019-08-08 18:58:30Z

3

I found a partial solution to this issue.

Interestingly, if I assign a linux-style path as my host-path (on Windows), then my pgdata-vol persists until Docker Desktop is restarted.

Instead of mounting to a real windows location

  volumes:
  - name: "pgdata-vol"
    hostPath:
      path: /c/temp/vols/pgdata

I use a "linux" location as my Windows hostPath

  volumes:
  - name: "pgdata-vol"
    hostPath:
      path: /tmp/vols/pgdata

Curiously, I cannot actually find this path from Windows. I presume this /tmp is local to my Docker Desktop instance.

This solution does not offer true persistence, but it has helped me to work around a roadblock that was impacting testing.

answered Aug 8, 2019 at 18:58

terrywb

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Wytrzymały Wiktor · Accepted Answer · 2019-07-30 07:36:52Z

2

+50

This is a known issue with Docker image on Windows. Right now it is not possible to correctly mount Windows directories as volumes. You may however try to workaround it by using a persistent Docker volume. For example:

  db:
    image: postgres
    environment:
      - POSTGRES_USER=<user>
      - POSTGRES_PASSWORD=<pass>
      - POSTGRES_DB=<db_name>
    ports:
      - <ports>
    volumes:
      - pgdata:<path>
    networks:
    - <network>

volumes:
  pgdata:

More Information:

Please let me know if that helped.

answered Jul 30, 2019 at 7:36

Wytrzymały Wiktor

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5 Comments

terrywb Over a year ago

Thanks. When I run my system with docker-compose, I create a volume as you have described above. I wish I knew of a way to mount a volume created as you describe to kubernetes.

Wytrzymały Wiktor Over a year ago

Are you familiar with Persistent Volumes?

terrywb Over a year ago

I had found that page, but I am unclear how to implement the options in my example. Ideally, I would simply like to replicate the type of volume that docker-compose creates (and persists).

Wytrzymały Wiktor Over a year ago

I see your point. I think it would be best if you ask this in a separate question. Would be easier and more transparent for all folks interested.

terrywb Over a year ago

I have created a new question. Thank you for the suggestion. stackoverflow.com/questions/57378980/…

wolmi · Accepted Answer · 2019-07-30 07:45:55Z

1

Have you tried using WSL? My setup for windows is WSL + Ubuntu + Docker for windows and I can mount volumes normally.

I've followed that tutorial to configure all my environment:

https://nickjanetakis.com/blog/setting-up-docker-for-windows-and-wsl-to-work-flawlessly

answered Jul 30, 2019 at 7:45

wolmi

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