Kubernetes 1.15 releases with extensibility around core Kubernetes APIs, cluster lifecycle stability, and more!

Update: On July 23rd, the Enhancements Lead of Kubernetes 1.15 at VMware, Kenny Coleman, published a “What's New in Kubernetes 1.15” video with Cloud Native Computing Foundation (CNCF). In the video, he explains in detail about the three new major features in Kubernetes 1.15, which include Dynamic HA Clusters with Kubeadm, Volume Cloning and CustomResourceDefinition (CRDs). Coleman also highlights each feature and explains its importance to users.

Watch the video below to know in detail about Kenny Coleman’s talk about Kubernetes 1.15.

https://www.youtube.com/watch?v=eq7dgHjPpzc

On June 19th, the Kubernetes team announced the release of Kubernetes 1.15, which consists of 25 enhancements, including 2 moving to stable, 13 in beta, and 10 in alpha. The key features of this release include extensibility around core Kubernetes APIs, cluster lifecycle stability, and usability improvements.

This is Kubernetes’ second release this year. The previous version Kubernetes 1.14, released three months ago, had 10 stable enhancements--the most amount of stable features revealed in a release.

In an interview to the New Stack, Claire Laurence, the team lead at Kubernetes said that in this release, “We’ve had a fair amount of features progress to beta. I think what we’ve been seeing a lot with these alpha and beta features as they progress is a lot of continued focus on stability and overall improvement before indicating that those features are stable.”

Let’s have a brief look at all the new features and updates.

#1 Extensibility around core Kubernetes APIs

The theme of the new developments around CustomResourceDefinitions is data consistency and native behavior. The Kubernetes team wants that a user should not notice whether the interaction is with a CustomResource or with a Golang-native resource. Hence, from v1.15 onwards, Kubernetes will check each schema against a restriction called “structural schema”. This enforces non-polymorphic and complete typing of each field in a CustomResource.

Out of the five enhancements, the ‘CustomResourceDefinition Defaulting’ is an alpha release. It is specified using the default keyword in the OpenAPI validation schema. Defaulting will be available as alpha in Kubernetes 1.15 for structural schemas. The other four enhancements are in beta which include:

CustomResourceDefinition Webhook Conversion

In Kubernetes, CustomResourceDefinitions gain the ability to convert between different versions on-the-fly, just like users are used to from native resources for the long term.

CustomResourceDefinition OpenAPI Publishing

OpenAPI publishing for CRDs will be available with Kubernetes 1.15 as beta, but only for structural schemas.

CustomResourceDefinitions Pruning

Pruning is the automatic removal of unknown fields in objects sent to a Kubernetes API. A field is unknown if it is not specified in the OpenAPI validation schema. It enforces that only data structures specified by the CRD developer are persisted to etcd. This is the behaviour of native resources, and will be available for CRDs as well, starting as beta in Kubernetes 1.15.

Admission Webhook Reinvocation & Improvements

In the earlier versions, mutating webhooks were only called once, in alphabetical order. An earlier run webhook cannot react on the output of webhooks, called later in the chain. With Kubernetes 1.15, mutating webhooks can opt-in into at least one re-invocation by specifying reinvocationPolicy: IfNeeded. If a later mutating webhook modifies the object, the earlier webhook will get a second chance.

#2 Cluster Lifecycle Stability and Usability Improvements

The cluster lifecycle building block, kubeadm, continues to receive features and stability work, which is needed for bootstrapping production clusters efficiently.

kubeadm has promoted high availability (HA) capability to beta, allowing users to use the familiar kubeadm init and kubeadm join commands to configure and deploy an HA control plane.

With kubeadm, certificate management has become more robust in 1.15, as it seamlessly rotates all the certificates before expiry.

The kubeadm configuration file API is moving from v1beta1 to v1beta2 in 1.15.

kubeadm now has its own new logo.

Continued Improvement of CSI

In Kubernetes 1.15, the Special Interests Groups (SIG) Storage enables migration of in-tree volume plugins to Container Storage Interface (CSI). SIG Storage worked on bringing CSI to feature parity with in-tree functionality, including functionality like resizing and inline volumes. SIG Storage introduces new alpha functionality in CSI that doesn’t exist in the Kubernetes Storage subsystem yet, like volume cloning.

Volume cloning enables users to specify another PVC as a “DataSource” when provisioning a new volume.

If the underlying storage system supports this functionality and implements the “CLONE_VOLUME” capability in its CSI driver, then the new volume becomes a clone of the source volume.

Additional feature updates

Support for go modules in Kubernetes Core

Continued preparation on cloud provider extraction and code organization. The cloud provider code has been moved to kubernetes/legacy-cloud-providers for easier removal later and external consumption.