Kubernetes Volume Mount with Replication Controllers - docker

Question

Found this example for Kubernetes EmptyDir volume
apiVersion: v1
kind: Pod
metadata:
name: www
spec:
containers:
- name: nginx
image: nginx
volumeMounts:
- mountPath: /srv/www
name: www-data
readOnly: true
- name: git-monitor
image: kubernetes/git-monitor
env:
- name: GIT_REPO
value: http://github.com/some/repo.git
volumeMounts:
- mountPath: /data
name: www-data
volumes:
- name: www-data
emptyDir: {}
I want to volume mount between 2 pods. I am creating these pods using 2 different Replication Controllers. The replication controllers looks like this
Replication Controller 1:
apiVersion: v1
kind: ReplicationController
metadata:
name: node-worker
labels:
name: node-worker
spec:
replicas: 1
selector:
name: node-worker
template:
metadata:
labels:
name: node-worker
spec:
containers:
-
name: node-worker
image: image/node-worker
volumeMounts:
- mountPath: /mnt/test
name: deployment-volume
volumes:
- name: deployment-volume
emptyDir: {}
Replication Controller 2:
apiVersion: v1
kind: ReplicationController
metadata:
name: node-manager
labels:
name: node-manager
spec:
replicas: 1
selector:
name: node-manager
template:
metadata:
labels:
name: node-manager
spec:
containers:
-
name: node-manager
image: image/node-manager
volumeMounts:
- mountPath: /mnt/test
name: deployment-volume
volumes:
- name: deployment-volume
emptyDir: {}
Can Kubernetes emptyDir volume be used for this scenario?

Answer 1

EmptyDir volumes are inherently bound to the lifecycle of a single pod and can't be shared amongst pods in replication controllers or otherwise. If you want to share volumes amongst pods, the best choices right now are NFS or gluster, in a persistent volume. See an example here: https://github.com/kubernetes/examples/blob/master/staging/volumes/nfs/README.md

Answer 2

Why do you want to share the volume mount between pods? This will not work reliably because you aren't guaranteed to have a 1:1 mapping between where pods in replication controller 1 and replication controller 2 are scheduled in your cluster.
If you want to share local storage between containers, you should put both of the containers into the same pod, and have each container mount the emptyDir volume.

Answer 3

You require three things to get this working. More info can be found here and some documentation here, but it's a little confusing at first.
This example mounts a NFS volume.
1. Create a PersistentVolume pointing to your NFS server
file : mynfssharename-pv.yaml
(update server to point to your server)
apiVersion: v1
kind: PersistentVolume
metadata:
name: mynfssharename
spec:
capacity:
storage: 1Gi
accessModes:
- ReadWriteMany
nfs:
server: yourservernotmine.yourcompany.com
path: "/yournfspath"
kubectl create -f mynfssharename-pv.yaml
2. Create a PersistentVolumeClaim to points to PersistentVolume mynfssharename
file : mynfssharename-pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: mynfssharename
spec:
accessModes:
- ReadWriteMany
resources:
requests:
storage: 1Gi
kubectl create -f mynfssharename-pvc.yaml
3. Add the claim to your ReplicationController or Deployment
spec:
containers:
- name: sample-pipeline
image: yourimage
imagePullPolicy: Always
ports:
- containerPort: 8080
name: http
volumeMounts:
# name must match the volume name below
- name: mynfssharename
mountPath: "/mnt"
volumes:
- name: mynfssharename
persistentVolumeClaim:
claimName: mynfssharename