Local Storage support for the Percona Operator for MySQL¶

Among the wide rage of volume types, available in Kubernetes, there are some which allow Pod containers to access part of the local filesystem on the node. Two such options provided by Kubernetes itself are emptyDir and hostPath volumes. More comprehensive setups require additional components, such as OpenEBS Container Attached Storage solution

emptyDir¶

The name of this option is self-explanatory. When Pod having an emptyDir volume is assigned to a Node, a directory with the specified name is created on this node and exists until this Pod is removed from the node. When the Pod have been deleted, the directory is deleted too with all its content. All containers in the Pod which have mounted this volume will gain read and write access to the correspondent directory.

The emptyDir options in the deploy/cr.yaml file can be used to turn the emptyDir volume on by setting the directory name.

hostPath¶

A hostPath volume mounts some existing file or directory from the node’s filesystem into the Pod.

The volumeSpec.hostPath subsection in the deploy/cr.yaml file may include path and type keys to set the node’s filesystem object path and to specify whether it is a file, a directory, or something else (e.g. a socket):

volumeSpec:
  hostPath:
    path: /data
    type: Directory

Please note, that hostPath directory is not created automatically! It should be created manually on the node’s filesystem. Also, it should have the attributives (access permissions, ownership, SELinux security context) which would allow Pod to access the correspondent filesystem objects according to pxc.containerSecurityContext and pxc.podSecurityContext.

hostPath is useful when you are able to perform manual actions during the first run and have strong need in improved disk performance. Also, please consider using tolerations to avoid cluster migration to different hardware in case of a reboot or a hardware failure.

More details can be found in the official hostPath Kubernetes documentation .

OpenEBS Local Persistent Volume Hostpath¶

Both emptyDir and hostPath volumes do not support Dynamic Volume Provisioning . Options that allow combining Dynamic Volume Provisioning with Local Persistent Volumes are provided by OpenEBS . Particularly, OpenEBS Local PV Hostpath allows creating Kubernetes Local Persistent Volumes using a directory (Hostpath) on the node. Such volume can be further accessed by applications via Storage Class and PersistentVolumeClaim .

Using it involves the following steps.

Install OpenEBS on your system along with the official installation guide .
Define a new Kubernetes Storage Class with OpenEBS with the YAML file (e. g. local-hostpath.yaml) as follows:
```
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: localpv
  annotations:
    openebs.io/cas-type: local
    cas.openebs.io/config: |
      - name: StorageType
        value: hostpath
      - name: BasePath
        value: /var/local-hostpath
provisioner: openebs.io/local
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer
```
Two things to edit in this example are the metadata.name key (you will use it as a storage class name) and the value option under the cas.openebs.io/config (it should point to an already existing directory on the local filesystem of your node).

When ready, apply the file with the kubectl apply -f local-hostpath.yaml command.

Now you can deploy the Operator and Percona XtraDB Cluster using this StorageClass in deploy/cr.yaml:

...
volumeSpec:
  persistentVolumeClaim:
    storageClassName: localpv
    accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 200Gi

Note

There are other storage options provided by the OpenEBS, which may be helpful within your cluster setup. Look at the OpenEBS for the Management of Kubernetes Storage Volumes blog post for more examples. Also, consider looking at the Measuring OpenEBS Local Volume Performance Overhead in Kubernetes post.

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Last update: 2024-10-16