Running Stateful Applications in Kubernetes: Storage Provisioning and Allocation
In the last part of this series, we explored how the concept of volumes brings persistence to containers. This article builds upon the understanding of volumes to introduce persistent volumes and claims, which form the robust storage infrastructure of Kubernetes.
To appreciate how Kubernetes manages storage pools that provide persistence to applications, we need to understand the architecture and the workflow related to application deployment.
Kubernetes is used in various roles — by developers, system administrators, operations, and DevOps teams. Each of these personas, if you will, interact with the infrastructure in a distinct way. The system administration team is responsible for configuring the physical infrastructure for running Kubernetes cluster. The operations team maintains the Kubernetes cluster through patching, upgrading, and scaling the cluster. DevOps teams deal with Kubernetes to configure CI/CD, monitoring, logging, rolling upgrades, and canary deployments. Developers consume the API and the resources exposed by the Kubernetes infrastructure. They are never expected to have visibility into the underlying physical infrastructure that runs the master and nodes.
Developers “ask” for the resources they need to run their applications through a declarative mechanism, typically described in YAML or JSON. The Kubernetes master is responsible for ensuring that the appropriate resources are selected as requested by the developers. But before it can do that, the administrators will need to provision the required compute, storage, and networking capacity.
For example, a developer may ask Kubernetes to schedule a pod backed by SSD running powered by a certain number of cores and memory. Assuming that the infrastructure is capable, Kubernetes master honors the request by choosing the right node(s) to run the pod.
To understand this concept, let’s look at the relationship between a pod and node. Nodes are pre-provisioned servers configured by administrators and operations team. Developers create pods that utilize the compute resources exposed by the nodes.
This architecture of Kubernetes enables clean separation of concerns among developers, administrators, and operations.
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Janakiram MSV is an analyst, advisor, and architect. Follow him on Twitter, Facebook and LinkedIn.