The csi-nfs module

The module provides CSI for managing NFS volumes and allows creating StorageClass in Kubernetes through Custom Resources NFSStorageClass.

System requirements and recommendations

Requirements

• Use stock kernels provided with supported distributions;
• Ensure the presence of a deployed and configured NFS server;
• To support RPC-with-TLS, enable CONFIG_TLS and CONFIG_NET_HANDSHAKE options in the Linux kernel.

Recommendations

For module pods to restart when the tlsParameters parameter is changed in the module settings, the pod-reloader module must be enabled (enabled by default).

RPC-with-TLS mode limitations

• Only one certificate authority (CA) is supported.
• For the mtls security policy, only one client certificate is supported.
• A single NFS server cannot simultaneously operate in different security modes: tls, mtls, and standard (non-TLS) mode.
• The tlshd daemon must not be running on the cluster nodes, otherwise it will conflict with the daemon of our module. To prevent conflicts when enabling TLS, the third-party tlshd is automatically stopped on the nodes and its autostart is disabled.

Quickstart guide

Note that all commands must be run on a machine that has administrator access to the Kubernetes API.

Enabling module

1. Enable the csi-nfs module. This will result in the following actions across all cluster nodes:

   • registration of the CSI driver;
   • launch of service pods for the csi-nfs components.

   kubectl apply -f - <<EOF
   apiVersion: deckhouse.io/v1alpha1
   kind: ModuleConfig
   metadata:
     name: csi-nfs
   spec:
     enabled: true
     version: 1
   EOF
   

2. Wait for the module to become Ready:

   kubectl get module csi-nfs -w
   

Creating a StorageClass

To create a StorageClass, you need to use the NFSStorageClass resource. Here is an example command to create such a resource:

kubectl apply -f - <<EOF
apiVersion: storage.deckhouse.io/v1alpha1
kind: NFSStorageClass
metadata:
  name: nfs-storage-class
spec:
  connection:
    host: 10.223.187.3
    share: /
    nfsVersion: "4.1"
  reclaimPolicy: Delete
  volumeBindingMode: WaitForFirstConsumer
EOF

A directory <directory from share>/<PV name> will be created for each PV.

Checking module health

You can verify the functionality of the module using the instructions in FAQ.

Selects the method to clean the volume before deleting the PV

Files with user data may remain on the volume to be deleted. These files will be deleted and will not be accessible to other users via NFS.

However, the deleted files’ data may be available to other clients if the server grants block-level access to its storage.

The volumeCleanup parameter will help you choose how to clean the volume before deleting it.

Caution. This option does not affect files already deleted by the client application.

Caution. This option affects only commands sent via the NFS protocol. The server-side execution of these commands is defined by:

• NFS server service;
• the file system;
• the level of block devices and their virtualization (e.g. LVM);
• the physical devices themselves.

Make sure the server is trusted. Do not send sensitive data to servers that you are not sure of.

SinglePass method

Used if volumeCleanup is set to RandomFillSinglePass.

The contents of the files are overwritten with a random sequence before deletion. The random sequence is transmitted over the network.

ThreePass method

Used if volumeCleanup is set to RandomFillThreePass.

The contents of the files are overwritten three times with a random sequence before deletion. The three random sequences are transmitted over the network.

Discard method

Used if volumeCleanup is set to Discard.

Many file systems implement support for solid-state drives, allowing the space occupied by a file to be freed at the block level without writing new data to extend the life of the solid-state drive. However, not all solid-state drives guarantee that the freed block data is inaccessible.

If volumeCleanup is set to Discard, file contents are marked as free via the falloc system call with the FALLOC_FL_PUNCH_HOLE flag. The file system will free the blocks fully used by the file, via the blkdiscard call, and the remaining space will be overwritten with zeros.

Advantages of this method:

• the amount of traffic does not depend on the size of the files, only on the number of files;
• the method can make old data unavailable in some server configurations;
• works for both hard disks and SSDs;
• can maximize SSD lifetime.