To support different use cases, Kubernetes allows the provisioning of different types of ephemeral volumes. In instances where both runtime and root partitions exist, the runtime partition is considered the default option for writeable storage. Pods store container images and container-writeable layers within the runtime partition by default. Kubernetes uses this runtime partition to identify and provide both shared access and isolation as required. Runtimes often use an additional partition for overlay file systems. A root partition is completely ephemeral, so it doesn’t support any performance SLAs, such as disk IOPS. Pods also utilize the root partition when creating image layers, container-writeable layers, and container logs for transient applications. In such a setup, pods use EmptyDir volumes to consume ephemeral storage in the root primary partition. The root partition holds the logs ( /var/log) and kubelet ( /var/lib/kubelet) directories and is shared among Kubernetes system daemons, user pods, and the underlying operating system. Kubernetes offers two approaches to creating the node’s primary partition, where ephemeral storage is deployed. While pods use the ephemeral storage framework to specify their transient local needs, Kubernetes relies on the storage framework to schedule pods appropriately while preventing pods from excessively using local node storage Ephemeral storage options Ephemeral storage is unstructured and shared between all pods running on the node, the container runtime, and other processes managed by the system. This can be done both at the pod level and at the container level for fine-grained storage management. In a Kubernetes cluster, you manage ephemeral storage by setting resource quotas and request limits across all non-terminal pods. Ephemeral storage is also considered crucial for sharing nonessential data within multi-container pods and injecting configuration data into a pod. In addition to this, pods in Kubernetes leverage ephemeral storage for functions such as caching, scratch space, and logs. Such applications intermittently rely on storage devices but don’t care whether data persists across pod restarts. How Kubernetes handles ephemeral storageĮphemeral storage is considered perfect for immutable applications and is used to handle the transient needs of pods running on cluster nodes. In this article, we’ll discuss how Kubernetes handles ephemeral storage and learn how these volumes are provisioned in operating clusters. While persistent volumes retain data irrespective of a pod’s lifecycle, ephemeral volumes last only for the lifetime of a pod and are deleted as soon as the pod terminates. Kubernetes supports two volume types - persistent and ephemeral - for different use cases. In Kubernetes, a volume represents a disk or directory that containers can write data onto or read data from, to handle cluster storage needs.
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