How to mimic '--volumes-from' in Kubernetes

Question

I\'m looking for a pattern that allows to share volumes between two containers running on the same pod in Kubernetes.

My use case is: I have a Ruby on Rails applicat

Answer 1

[update-2016-8] In latest Kubernetes release, you can use a very nice feature named init-container to replace the postStart part in my answer below, which will make sure the container order.

apiVersion: v1
kind: Pod
metadata:
  name: javaweb-2
spec:
  initContainers:
  - name: war
    image: resouer/sample:v2
    command: ["cp", "/sample.war", "/app"]
    volumeMounts:
    - mountPath: /app
      name: app-volume
  containers:
  - name: tomcat
    image: resouer/mytomcat:7.0
    command: ["sh","-c","/root/apache-tomcat-7.0.42-v2/bin/start.sh"]
    volumeMounts:
    - mountPath: /root/apache-tomcat-7.0.42-v2/webapps
      name: app-volume
    ports:
    - containerPort: 8080
      hostPort: 8001
  volumes:
  - name: app-volume
    emptyDir: {}

NOTE: initContainer is still a beta feature so the work version of this yaml is actually like: http://kubernetes.io/docs/user-guide/production-pods/#handling-initialization, please notice the pod.beta.kubernetes.io/init-containers part.

---original answer begin---

Actually, you can. You need to use container life cycle handler to control what files/dirs you want to share with other containers. Like:

---
apiVersion: v1
kind: Pod
metadata:
    name: server
spec:
    restartPolicy: OnFailure
    containers:
    - image: resouer/sample:v2
      name: war
      lifecycle:
        postStart:
          exec:
            command:
              - "cp"
              - "/sample.war"
              - "/app"
      volumeMounts:
      - mountPath: /app
        name: hostv1 
    - name: peer
      image: busybox
      command: ["tail", "-f", "/dev/null"]
      volumeMounts:
      - name: hostv2
        mountPath: /app/sample.war
    volumes:
    - name: hostv1
      hostPath:
          path: /tmp
    - name: hostv2
      hostPath:
          path: /tmp/sample.war

Please check my gist for more details:

https://gist.github.com/resouer/378bcdaef1d9601ed6aa

And of course you can use emptyDir. Thus, war container can share its /sample.war to peer container without mess peer's /app directory.

If we can tolerate /app been overridden, it will be much simpler:

---
apiVersion: v1
kind: Pod
metadata:
  name: javaweb-2
spec:
  restartPolicy: OnFailure
  containers:
  - image: resouer/sample:v2
    name: war
    lifecycle:
      postStart:
        exec:
          command:
            - "cp"
            - "/sample.war"
            - "/app"
    volumeMounts:
    - mountPath: /app
      name: app-volume
  - image: resouer/mytomcat:7.0
    name: tomcat
    command: ["sh","-c","/root/apache-tomcat-7.0.42-v2/bin/start.sh"]
    volumeMounts:
    - mountPath: /root/apache-tomcat-7.0.42-v2/webapps
      name: app-volume
    ports:
    - containerPort: 8080
      hostPort: 8001 
  volumes:
  - name: app-volume
    emptyDir: {}