docker - Is it possible to mount different pods to the same portion of a local persistent volume?

Question

Basically, I'm creating a StatefulSet deployment with 2 pods (single host cluster), I would like to that each pod will be able to mount to a base folder in the host, and to a subfolder beneath it:

Base folder mount: /mnt/disks/ssd

Pod#1 - /mnt/disks/ssd/pod-1

Pod#2 - /mnt/disks/ssd/pod-2

I've managed only to mount the first pod to the base folder, but the 2nd folder cannot mount (as the volume is already taken)

This is the volume:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: example-local-pv
spec:
  capacity:
    storage: 5Gi 
  accessModes:
  - ReadWriteOnce
  persistentVolumeReclaimPolicy: Delete
  storageClassName: local-storage
  local:
    path: /mnt/disks/ssd
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - ubuntukuber

This is the usage in the stateful set:

apiVersion: apps/v1beta1
kind: StatefulSet
metadata:
  name: app
  namespace: test-ns
spec:
  serviceName: app
  replicas: 2
....
....
        volumeMounts:
          - name: data
            mountPath: /var/lib/app/data
volumeClaimTemplates:
    - metadata:
        name: data
      spec:
        accessModes: [ "ReadWriteOnce" ]
        storageClassName: "local-storage"
        resources:
          requests:
            storage: 2Gi

So, i basically would like that each replica would use its own subfolder - how can one achieve it?

== EDIT ==

I've made some progress, i'm able to mount several replicas into the same mount, using the following YAMLs (the app i'm trying to do it on is rabbitmq - so i'll leave the app name as is)

---
kind: PersistentVolume
apiVersion: v1
metadata:
  name: pv-local
  namespace: test-rabbitmq
  labels:
    type: local
spec:
  storageClassName: local
  capacity:
    storage: 6Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/mnt/disks"
---
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: hostpath-pvc
  namespace: test-rabbitmq
spec:
  storageClassName: local
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 3Gi
  selector:
    matchLabels:
      type: local
---

In the StatefulSet i'm declaring this volume:

  volumes:
    - name: rabbitmq-data
      persistentVolumeClaim:
        claimName: hostpath-pvc

And mounting "rabbitmq-data".

Both pods mount to the same folder, but will not create subfolders - this is no terrible situation as by default there are rabbitmq's subfolders - i'll try to expand it into each pod to use a subfolder

Answer 1

I am able to achieve the above scenario, what you need is "claimRef" in your pv to bind your PVC. Please have a look at following pv json and statefulset json

PV-0.json

{
  "kind": "PersistentVolume",
  "apiVersion": "v1",
  "metadata": {
    "name": "pv-data-vol-0",
    "labels": {
      "type": "local"
    }
  },
  "spec": {
    "capacity": {
      "storage": "10Gi"
    },
    "accessModes": [
      "ReadWriteOnce"
    ],
    "storageClassName": "local-storage",
    "local": {
      "path": "/prafull/data/pv-0"
    },
    "claimRef": {
      "namespace": "default",
      "name": "data-test-sf-0"
    },
    "nodeAffinity": {
      "required": {
        "nodeSelectorTerms": [
          {
            "matchExpressions": [
              {
                "key": "kubernetes.io/hostname",
                "operator": "In",
                "values": [
                  "ip-10-0-1-46.ec2.internal"
                ]
              }
            ]
          }
        ]
      }
    }
  }
}

PV-1.json

{
  "kind": "PersistentVolume",
  "apiVersion": "v1",
  "metadata": {
    "name": "pv-data-vol-1",
    "labels": {
      "type": "local"
    }
  },
  "spec": {
    "capacity": {
      "storage": "10Gi"
    },
    "accessModes": [
      "ReadWriteOnce"
    ],
    "storageClassName": "local-storage",
    "local": {
      "path": "/prafull/data/pv-1"
    },
    "claimRef": {
      "namespace": "default",
      "name": "data-test-sf-1"
    },
    "nodeAffinity": {
      "required": {
        "nodeSelectorTerms": [
          {
            "matchExpressions": [
              {
                "key": "kubernetes.io/hostname",
                "operator": "In",
                "values": [
                  "ip-10-0-1-46.ec2.internal"
                ]
              }
            ]
          }
        ]
      }
    }
  }
}

Statefulset.json

{
  "kind": "StatefulSet",
  "apiVersion": "apps/v1beta1",
  "metadata": {
    "name": "test-sf",
    "labels": {
      "state": "test-sf"
    }
  },
  "spec": {
    "replicas": 2,
    "template": {
      "metadata": {
        "labels": {
          "app": "test-sf"
        },
        "annotations": {
          "pod.alpha.kubernetes.io/initialized": "true"
        }
      }
      ...
      ...
    },
    "volumeClaimTemplates": [
      {
        "metadata": {
          "name": "data"
        },
        "spec": {
          "accessModes": [
            "ReadWriteOnce"
          ],
          "storageClassName": "local-storage",
          "resources": {
            "requests": {
              "storage": "10Gi"
            }
          }
        }
      }
    ]
  }
}

There will be two pods created test-sf-0 and test-sf-1 which in-turn will be created two PVC data-test-sf-0 and data-test-sf-1 which will be bound to PV-0 and Pv-1 respectively. Hence test-sf-0 will write to the location specified in PV-0 and test-sf-1 will write in location specified on PV-1. Hope this helps.