A new Japanese era and its associated calendar begin on May 1, 2019. Microsoft as a company has been planning and preparing for the required changes for some time.
Azure customers can deploy updates to Microsoft and third-party products to the Azure virtual machines that they manage, including operating systems, development frameworks and applications, as updates become available. You can find details about Microsoft products in the Updates for May 2019 Japanese era change KB Article.
Azure PaaS services rely on support from the underlying operating system and development frameworks for date-related functionality. We will gradually deploy the relevant new era updates to the Azure infrastructure as they become available over the coming weeks. Windows updates to support the new era have already been deployed for Azure App Service in the two Azure regions in Japan.