A Kubernetes cluster is a group of one or more servers that work together. The goal is to provide high availability, scalability and resource efficiency for your applications. Each server in the cluster has storage space available for containers to use. This blog post will explore how Kubernetes clusters store data and what type of options you have when it comes to storing data on your cluster.
Kubernetes storage is managed by a set of abstractions called volumes. Volumes are just directories in the file system that have been exposed to containers, and they store data independently from their underlying raw block devices. You can think about them as being similar to hard drives or flash drives which you attach to your computer so it’s able to store data. You can then access that storage space from inside or outside the machine, and even manage it if need be.
Volumes are initialized in each node of your cluster when you start up pods (which is what runs containers inside Kubernetes). Each pod running on a node has an associated volume which includes both the directory and the storage device. All containers inside a pod share these directories, so if you write data to one of them it will be visible from all other containers in that pod.
When pods are removed or deleted, their volumes stick around until they’re garbage collected by the system (which often happens automatically). This means your applications can always access old data even if pods are deleted.
Kubernetes has a volume type abstraction that can be implemented by storage providers and used in any scenario they want to support. This means you’re not limited when it comes to what types of storage you can use with your clusters – in fact, there’s already an ecosystem of volume providers built around Kubernetes so you have plenty of options to choose from.
Some volume types are managed by the cluster itself, while others are managed by external storage providers that support them directly through cloud services or other APIs. This means your cluster administrator can manage shared storage for all nodes in a unified way instead of having to provision and configure storage devices on each node manually.
Volumes can be used to preserve data across pod restarts or even cluster restarts, so if a container suddenly dies, you won’t lose the application state. This is particularly essential for stateful applications like databases. There’s also a method to mount externally provisioned volumes directly from pods, allowing you to use third-party tools like cloud disks
Finally, volumes may be mounted in Kubernetes in a variety of ways. The volume management API enables you to mount them manually, but there’s also support for mounting directories from other pods in the cluster. There are even choices for automatically generating volumes at startup, allowing stateless applications to run inside pods without having to worry about how they save