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I have an inhouse Kubernetes cluster running on bare-metal and it consists of 5 nodes (1 master and 4 workers). I set up an NFS server on the master natively and launched the nfs-client in the K8s to have nfs dynamic provisioner. Everything are working properly and I am able to use my applications just by defining a persistent volume claim BUT I can't find my data on the disk.

Every time I launch an application, the nfs-client creates a new directory at the path of my nfs server with the correct name but all of these directories are empty. So my question is where are my data?

I am using the helm chart of the nfs client. This is an example of the created but empty directory at my nfs server path:

/var/nfs/general$ tree
.
├── 166-postgres-claim-pvc-37146254-db50-4293-a9f7-13097689610a
│   └── data
├── 166-registry-claim-pvc-fe337e34-d9a5-4266-8178-f67973894584
├── 166-registry-slave-claim-registry-slave-0-pvc-b18d430b-e1fc-4eeb-bd12-cab9340bed69
├── 166-rtspdata-claim-pvc-bf9bc1e3-412f-4627-ade4-50817478308e
├── 172-postgres-claim-pvc-087538cf-5b67-4789-8d8b-117d41c3fe02
│   └── data
├── 172-registry-claim-pvc-7b7d9bb6-a636-4f78-b2fe-924473cb47ab
├── 172-registry-slave-claim-registry-slave-0-pvc-34e62524-fca0-48dd-ba29-b4cf178ca028
├── 172-rtspdata-claim-pvc-211a1aac-409f-431c-b78d-5b87b9017625
├── 173-postgres-claim-pvc-b901449a-0ce7-4ecf-8dfc-e6371dd3a9b4
│   └── data
├── 173-registry-claim-pvc-cd842cde-a3f7-4d54-94d6-c018e42ec495
├── 173-rtspdata-claim-pvc-a95c5748-ebed-4045-98b2-a04e534e0cf6
├── archived-161-postgres-claim-pvc-01cc1ff2-8cc8-4161-8d85-00cb6562e10e
│   └── data
├── archived-161-registry-claim-pvc-9b626e01-a565-4214-b94e-b7ba1e206a5e
├── archived-161-rtspdata-claim-pvc-b079c7e2-248e-4245-b243-5ff7dc3afa82
├── archived-162-postgres-claim-pvc-188af7ca-106d-4f2f-8905-9d7b391e9dce
│   └── data
├── archived-162-postgres-claim-pvc-356e4632-19e2-4ac9-8400-e00d39621b7c
│   └── data
├── archived-162-postgres-claim-pvc-45372032-979f-4ced-be35-15ec67a322b7
│   └── data
├── archived-162-postgres-claim-pvc-6d5e1f01-ad5b-45cc-9eef-654275e3ecd2
│   └── data
├── archived-162-postgres-claim-pvc-cbf4d4ca-b9d1-4d1c-88be-621eeb3680fb
│   └── data
├── archived-162-postgres-claim-pvc-eaa32a4c-9768-469a-ad85-1e1b682c376d
│   └── data
├── archived-162-postgres-claim-pvc-f517586b-e132-4a38-8ec9-18f6d5ca000e
│   └── data
├── archived-162-registry-claim-pvc-1796642a-d639-4ede-8204-1779c029aa4e
│   └── rethinkdb_data
5

I have reproduced this scenario in my test environment and I could find my data normally. To reproduce it I've followed these steps.

Make sure that you follow every steps. Editing this file needs root access; therefore you will need to use sudo with your command. You can also open the file in any of your personal favorite text editors.

1 - Installed and configured my NFS Server on my Master Node (Debian Linux, this might change depending on your Linux distribution):

Before installing the NFS Kernel server, we need to update our system’s repository index:

$ sudo apt-get update

Now, run the following command in order to install the NFS Kernel Server on your system:

$ sudo apt install nfs-kernel-server

Create the Export Directory

$ sudo mkdir -p /mnt/nfs_server_files

As we want all clients to access the directory, we will remove restrictive permissions of the export folder through the following commands (this may vary on your set-up according to your security policy):

$ sudo chown nobody:nogroup /mnt/nfs_server_files
$ sudo chmod 777 /mnt/nfs_server_files

Assign server access to client(s) through NFS export file

$ sudo nano /etc/exports

Inside this file, add a new line to allow access from other servers to your share.

/mnt/nfs_server_files        10.128.0.0/24(rw,sync,no_subtree_check)

You may want to use different options in your share. 10.128.0.0/24 is my k8s internal network.

Export the shared directory and restart the service to make sure all configuration files are correct.

$ sudo exportfs -a
$ sudo systemctl restart nfs-kernel-server

Check all active shares:

$ sudo exportfs
/mnt/nfs_server_files
                10.128.0.0/24

2 - Install NFS Client on all my Worker Nodes:

$ sudo apt-get update
$ sudo apt-get install nfs-common

At this point you can make a test to check if you have access to your share from your worker nodes:

$ sudo mkdir -p /mnt/sharedfolder_client
$ sudo mount kubemaster:/mnt/nfs_server_files /mnt/sharedfolder_client

Notice that at this point you can use the name of your master node. K8s is taking care of the DNS here. Check if the volume mounted as expected and create some folders and files to male sure everything is working fine.

$ cd /mnt/sharedfolder_client
$ mkdir test
$ touch file

Go back to your master node and check if these files are at /mnt/nfs_server_files folder.

3 - Install NFS Client Provisioner.

Install the provisioner using helm:

$ helm install --name ext --namespace nfs --set nfs.server=kubemaster --set nfs.path=/mnt/nfs_server_files stable/nfs-client-provisioner

Notice that I've specified a namespace for it. Check if they are running:

$ kubectl get pods -n nfs
NAME                                         READY   STATUS      RESTARTS   AGE
ext-nfs-client-provisioner-f8964b44c-2876n   1/1     Running     0          84s

At this point we have a storageclass called nfs-client:

$ kubectl get storageclass -n nfs
NAME         PROVISIONER                                AGE
nfs-client   cluster.local/ext-nfs-client-provisioner   5m30s

We need to create a PersistentVolumeClaim:

$ more nfs-client-pvc.yaml

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  namespace: nfs 
  name: test-claim
  annotations:
    volume.beta.kubernetes.io/storage-class: "nfs-client"
spec:
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 1Mi
$ kubectl apply -f nfs-client-pvc.yaml

Check the status (Bound is expected):

$ kubectl get persistentvolumeclaim/test-claim -n nfs
NAME         STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
test-claim   Bound    pvc-e1cd4c78-7c7c-4280-b1e0-41c0473652d5   1Mi        RWX            nfs-client     24s

4 - Create a simple pod to test if we can read/write out NFS Share:

Create a pod using this yaml:

apiVersion: v1
kind: Pod
metadata:
  name: pod0
  labels:
    env: test
  namespace: nfs  
spec:
  containers:
  - name: nginx
    image: nginx
    imagePullPolicy: IfNotPresent
    volumeMounts:
      - name: nfs-pvc
        mountPath: "/mnt"
  volumes:
    - name: nfs-pvc
      persistentVolumeClaim:
        claimName: test-claim
$ kubectl apply -f pod.yaml

Now, let's dig inside this pod:

$ kubectl exec -ti -n nfs pod0 -- bash

Let's list all mounted volumes on our pod:

root@pod0:/# df -h
Filesystem                                                                                Size  Used Avail Use% Mounted on
overlay                                                                                   9.8G  6.1G  3.3G  66% /
tmpfs                                                                                      64M     0   64M   0% /dev
tmpfs                                                                                     7.4G     0  7.4G   0% /sys/fs/cgroup
kubemaster:/mnt/nfs_server_files/nfs-test-claim-pvc-4550f9f0-694d-46c9-9e4c-7172a3a64b12  9.8G  5.8G  3.6G  62% /mnt
/dev/sda1                                                                                 9.8G  6.1G  3.3G  66% /etc/hosts
shm                                                                                        64M     0   64M   0% /dev/shm
tmpfs                                                                                     7.4G   12K  7.4G   1% /run/secrets/kubernetes.io/serviceaccount
tmpfs                                                                                     7.4G     0  7.4G   0% /proc/acpi
tmpfs                                                                                     7.4G     0  7.4G   0% /sys/firmware

As we can see, we have a NFS volume mounted on /mnt. (Important to notice the path kubemaster:/mnt/nfs_server_files/nfs-test-claim-pvc-4550f9f0-694d-46c9-9e4c-7172a3a64b12)

Let's check it:

root@pod0:/# cd /mnt
root@pod0:/mnt# ls -la
total 8
drwxrwxrwx 2 nobody nogroup 4096 Nov  5 08:33 .
drwxr-xr-x 1 root   root    4096 Nov  5 08:38 ..

It's empty. Let's create some files:

$ for i in 1 2 4 5 6; do touch file$i; done;
$ ls -l 
total 8
drwxrwxrwx 2 nobody nogroup 4096 Nov  5 08:58 .
drwxr-xr-x 1 root   root    4096 Nov  5 08:38 ..
-rw-r--r-- 1 nobody nogroup    0 Nov  5 08:58 file1
-rw-r--r-- 1 nobody nogroup    0 Nov  5 08:58 file2
-rw-r--r-- 1 nobody nogroup    0 Nov  5 08:58 file4
-rw-r--r-- 1 nobody nogroup    0 Nov  5 08:58 file5
-rw-r--r-- 1 nobody nogroup    0 Nov  5 08:58 file6

Now let's where are these files on our NFS Server (Master Node):

$ cd /mnt/nfs_server_files
$ ls -l 
total 4
drwxrwxrwx 2 nobody nogroup 4096 Nov  5 09:11 nfs-test-claim-pvc-4550f9f0-694d-46c9-9e4c-7172a3a64b12
$ cd nfs-test-claim-pvc-4550f9f0-694d-46c9-9e4c-7172a3a64b12/
$ ls -l 
total 0
-rw-r--r-- 1 nobody nogroup 0 Nov  5 09:11 file1
-rw-r--r-- 1 nobody nogroup 0 Nov  5 09:11 file2
-rw-r--r-- 1 nobody nogroup 0 Nov  5 09:11 file4
-rw-r--r-- 1 nobody nogroup 0 Nov  5 09:11 file5
-rw-r--r-- 1 nobody nogroup 0 Nov  5 09:11 file6

And here are the files we just created inside our pod!

  • Thank you for your detailed answer, these steps were exactly what I did and as I said everything is working properly. Yesterday I tested my cluster with another shared pvc and I was able to see the data on the disk (so proves that everything is good). My suggestion is for some reason RethinkDB pod is not able to mount the PV and it is just using the local storage and this is what I want to investigate more but because this answer is so detailed and cover all the requeired steps to set up an NFS provisioner I will accept it. – AVarf Nov 5 '19 at 12:21
  • Great news. I'm glad you could solve your problem. If it happens again just follow the instructions I posted to login into the pod and check if everything is mounted and working as expected. – mWatney Nov 5 '19 at 13:28

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