Help Center/ Cloud Container Engine/ User Guide (Paris Regions)/ Storage/ Ephemeral Volumes (emptyDir)/ Overview
Updated on 2024-01-26 GMT+08:00
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Overview

Introduction

Some applications require additional storage, but whether the data is still available after a restart is not important. For example, although cache services are limited by memory size, cache services can move infrequently used data to storage slower than memory. As a result, overall performance is not impacted significantly. Other applications require read-only data injected as files, such as configuration data or secrets.

Ephemeral volumes (EVs) in Kubernetes are designed for the above scenario. EVs are created and deleted together with pods following the pod lifecycle.

Common EVs in Kubernetes:
  • emptyDir: empty at pod startup, with storage coming locally from the kubelet base directory (usually the root disk) or memory. emptyDir is allocated from the EV of the node. If data from other sources (such as log files or image tiering data) occupies the temporary storage, the storage capacity may be insufficient.
  • ConfigMap: Kubernetes data of the ConfigMap type is mounted to pods as data volumes.
  • Secret: Kubernetes data of the Secret type is mounted to pods as data volumes.

emptyDir Types

CCE provides the following emptyDir types:
  • Using a Temporary Path: Kubernetes-native emptyDir type. Its lifecycle is the same as that of a pod. Memory can be specified as the storage medium. When the pod is deleted, the emptyDir volume is deleted and its data is lost.
  • Using a Local EV: Local data disks in a node form a storage pool (VolumeGroup) through LVM. LVs are created as the storage medium of emptyDir and mounted to containers. LVs deliver better performance than the default storage medium of emptyDir.

Constraints

  • Local EVs are supported only when the cluster version is v1.21.2-r0 or later and the everest add-on version is 1.2.29 or later.
  • Do not manually delete the corresponding storage pool or detach data disks from the node. Otherwise, exceptions such as data loss may occur.
  • Ensure that the /var/lib/kubelet/pods/ directory is not mounted to the pod on the node. Otherwise, the pod, mounted with such volumes, may fail to be deleted.