Container Engine for Kubernetes now supports Kubernetes version 1.19.7, in addition to versions 1.18.10, 1.17.13, and 1.16.15. Oracle recommends you upgrade your Kubernetes environment to version 1.19.7. With the availability of support for Kubernetes version 1.19.7, Container Engine for Kubernetes will cease support for Kubernetes versions 1.17.9, 1.16.15, and 1.16.8 on April 17th 2021.

Note the following:

• You can upgrade control plane nodes through unsupported minor versions. Kubernetes requires that you upgrade control plane nodes one minor version at a time. So if a control plane node is running Kubernetes version 1.15.7 (an unsupported minor version), upgrade it to Kubernetes version 1.16.8 (also an unsupported minor version), before upgrading it to 1.17.13.
• Kubernetes version 1.19 is built with golang version 1.15. Golang no longer supports x509 certificates that contain only CommonName. Before upgrading to Kubernetes version 1.19, Oracle recommends you check whether any clusters have admission webhooks that use an x509 certificate containing only CommonName. If there is such a cluster, update the admission webhook to use a new x509 certificate that contains a Subject Alternative Name (SAN). If you don't update the admission webhook, kube-apiserver cannot call it. As a result, any deployment dependent on the admission webhook will not be deployed in the cluster.
• Container Engine for Kubernetes will cease support for Kubernetes version 1.16.15 and 1.16.8 on April 17th, 2021. As a result, you will no longer be able to:
  • create new clusters running Kubernetes versions 1.16.15 and 1.16.8
  • add new node pools to existing clusters running Kubernetes versions 1.16.15 and 1.16.8

  (Note that although Kubernetes version 1.17.9 is no longer supported, it is still available to provision new clusters and new node pools).

• If you currently have existing clusters running Kubernetes versions 1.17.9, 1.16.15, or 1.16.8, Oracle strongly recommends you immediately upgrade those clusters to Kubernetes versions 1.19.7, 1.18.10, or 1.17.13.

To upgrade a cluster to a new Kubernetes minor version:

1. Upgrade the Kubernetes version running on the control plane by following the instructions here. 
2. Having upgraded the control plane, upgrade the Kubernetes version running on worker nodes in a node pool by following the instructions here.

Note:

Always follow the Kubernetes skew policy for Kubernetes minor version support.

Example skew policy:

• Kubernetes control plane nodes are at version 1.19.7
• Kubernetes worker nodes must be at version 1.19.7, 1.18.10, or 1.17.13

Note that although the worker nodes in a node pool must follow the Kubernetes skew policy, you do not have to upgrade them one minor version at a time.

For more information, see Upgrading Clusters to Newer Kubernetes Versions.