Download Kubernetes 1.21

Version 1.21 of Kubernetes has been released. Kubernetes is an open source and cross-platform system for managing, deploying and running applications in containers. It was originally designed by Google, but is now published by the Linux Foundation. Sufficient release notes for version 1.21 can be found on this page, these are briefly the most important changes:

CronJobs Graduate to Stable!

CronJobs (previously ScheduledJobs) has been a beta feature since Kubernetes 1.8! With 1.21 we get to finally see this widely used API graduate to stable.

CronJobs are meant for performing regular scheduled actions such as backups, report generation, and so on. Each of those tasks should be configured to recur indefinitely (for example: once a day / week / month); you can define the point in time within that interval when the job should start.

Immutable Secrets and ConfigMaps

Immutable Secrets and ConfigMaps add a new field to those resource types that will reject changes to those objects if set. Secrets and ConfigMaps by default are mutable which is beneficial for pods that are able to consume changes. Mutating Secrets and ConfigMaps can also cause problems if a bad configuration is pushed for pods that use them.

By marking Secrets and ConfigMaps as immutable you can be sure your application configuration won’t change. If you want to make changes you’ll need to create a new, uniquly named Secret or ConfigMap and deploy a new pod to consume that resource. Immutable resources also have scaling benefits because controllers do not need to poll the API server to watch for changes. This feature has graduated to stable in Kubernetes 1.21.

IPv4/IPv6 dual stack support

IP addresses are a consumable resource that cluster operators and administrators need to make sure are not exhausted. In particular, public IPv4 addresses are now scarce. Having dual-stack support enables native IPv6 routing to pods and services, whilst still allowing your cluster to talk IPv4 where needed. Dual-stack cluster networking also improves a possible scaling limitation for workloads.

Dual-stack support in Kubernetes means that pods, services, and nodes can get IPv4 addresses and IPv6 addresses. In Kubernetes 1.21 dual stack networking has graduated from alpha to beta, and is now enabled by default.

Graceful Node Shutdown

Graceful Node shutdown also graduated to beta with this release (and will now be available to a much larger group of users)! This is a hugely beneficial feature that allows the kubelet to be aware of node shutdown, and gracefully terminate pods that are scheduled to that node.

Currently, when a node shuts down, pods do not follow the expected termination lifecycle and are not shut down gracefully. This can introduce problems with a lot of different workloads. Going forward, the kubelet will be able to detect imminent system shutdown through systemd, then inform running pods so they can terminate as gracefully as possible.

PersistentVolume Health Monitor

Persistent Volumes (PV) are commonly used in applications to get local, file-based storage. They can be used in many different ways and help users migrate applications without needing to re-write storage backends.

Kubernetes 1.21 has a new alpha feature which allows PVs to be monitored for health of the volume and marked accordingly if the volume becomes unhealthy. Workloads will be able to react to the health state to protect data from being written or read from a volume that is unhealthy.

Reducing Kubernetes Build Maintenance

Previously Kubernetes has maintained multiple build systems. This has often been a source of friction and complexity for new and current contributors.

Over the last release cycle, a lot of work has been put in to simplify the build process, and standardize on the native Golang build tools. This should empower broader community maintenance, and lower the barrier to entry for new contributors.