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Upgrade your AKS Kubernetes version before 27 February 2020
You're receiving this email because you are using the Azure Kubernetes Service (AKS).
We detected that one or more AKS clusters for the Subscription ID(s) listed in the Account Information section are using Kubernetes v1.13 or lower. AKS will be retiring v1.13 on 27 February 2020. To stay within supported versions and SLO please upgrade your clusters to 1.14 or higher.
How to Upgrade AKS Kubernetes version?
[Note: As we migrate from MSDN, this question has been posted by an Azure Cloud Engineer as a frequently asked question.] Source: MSDN Thread Link