Hello @ashok hirpara ,
Microsoft Azure periodically performs updates across the globe to improve the reliability, performance, and security of the host infrastructure that underlies VMs. Many of these updates, including memory-preserving updates, are performed without any impact on your VMs or cloud services. However, some updates do require a reboot. In such cases, the VMs are shut down while we patch the infrastructure, and then the VMs are restarted.
The mail reason for the downtime you experience is due to the above reason.
There can be other instances also like Host maintenance, windows critical and security update, unplanned maintenance, storage issues, network related issues etc.
Azure services by Microsoft offers 99.95 percent Azure SLA and above. At the same time, the best way to protect an application that's running on Azure against VM reboots and downtime is to configure the VMs for high availability.
To provide this level of redundancy to your application, we recommend that you group two or more VMs in an availability set. This configuration ensures that during either a planned or unplanned maintenance event, at least one VM is available
Please mark as "Accept the answer" if the above steps helps you. Others with similar issues can also follow the solution as per your suggestion
Regards,
Manu