Managing Stateful Applications in Kubernetes

Stateful applications, such as database services and message brokers, record and manage the information generated within an enterprise platform. Though Kubernetes has always supported stateless applications — which are horizontally scalable due to the interchangeability of each pod — stateful applications require stronger guarantees for the storage they use.

Why the need for extra guarantees when it comes to stateful vs stateless? Whereas the storage used by stateless containerized applications can simply be re-initialized when a pod is rescheduled to a different node in the cluster, stateful applications are recording business-critical information that must be preserved at all costs — that requires persistent storage with an independent lifetime.

In Kubernetes, persistent volumes fill that role and can be created using a variety of storage provisioners. The actual back-end storage services each provisioner interfaces with is responsible for providing adequate data protection, such as backup/restore and high availability, and other data management features. With data protection, high availability, and flexible provisioning across the cluster all outside the scope of Kubernetes, what can you do to help ensure those things for your Kubernetes deployments?

Kubernetes deployment persistent volumes are used to create a layer of abstraction between pods and their provisioned storage, allowing each to be managed separately. Pods use a persistent volume claim as a request for storage that is matched to a persistent volume by the Kubernetes cluster.

In both static and dynamic provisioning scenarios, stateful applications have a very real need for reliable storage that is resilient against failure, and data protection features, such as backup and restore. In and of itself, these facilities are not provided by Kubernetes, but are instead delegated to the provisioner used and the storage backend. Users have to find outside solutions, such as Trident and Cloud Volumes ONTAP.

Trident provisions new persistent container storage that benefit from all of NetApp’s data management capabilities. Using stateful sets simplifies the deployment of all stateful applications by automating much of the required provisioning and administrative activity. If a pod in a stateful set goes down, Kubernetes will automatically bind a new instantiation of the pod to the dynamically provisioned persistent volume it was previously using.

Stateful applications in Kubernetes require persistent storage with an independent lifecycle from their pods. This can be achieved using persistent volumes directly, however, stateful sets and dynamic provisioning provide a solution that is easier to manage and scale up. Dynamically provisioning storage for stateful sets using Trident and Cloud Volumes ONTAP provides the data protection, high availability, and flexible storage management that is a must for reliably storing enterprise information.

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