Different cases of Azure VM 'reboots'

Full article: https://vunvulearadu.blogspot.ro/2018/04/different-cases-of-azure-vm-reboots.html

This post is focusing on different types of maintenance activities that can happen on your Azure Virtual Machine (VM). Depending on the actions that need to be done on your VM, this can have a direct or indirect impact on the machine availability or performance. 

Impact types

First of all, let's identify how a machine can be impacted by different maintenance activities. We do not include in this discussion cases like outages or disasters.

• Performance decrease: During a live migration of a machine, the performance of the machine can be lower than usual. This happens because of the live migration of a machine from one physical hardware to another that consumes resources.
• Pause: For a short period of time the machine is paused, but without data loss or connectivity problems (E.g., RDP connection is maintained, but delayed for a short period of time).
• Unplanned reboot: There are isolated cases when the VM needs a restart. In this situation, there is a short period of downtime until the machine restarts.
• Loss temporary drive: In specific situations, the temporary drive of the machine is lost. This shall not impact the applications that are running on the machine because the temporary drive should be used only for temporary data. 
• Planned reboot: In this situation in the time window specified by the user when system redeploy is allowed, Azure initiates a system update that might request a system reboot. 

Impact situations

There are 3 types of cases when our machine availability is impacted.

• Unplanned hardware maintenance: This is one of the most impressive scenarios. The platform can predict a hardware failure and trigger a migration from one physical hardware to another. This migration is done using live migrations technology that reduces the impact on the machine.
• Unexpected downtime: It is represented by the cases when physical hardware fails (E.g., disk failure, network failure) and the only thing that is possible to do is to migrate the machine to another hardware on another rack or datacenter. In this situations, the machine is down for a specific time. Even if the temporary disk can be lost, the data and OS disk are preserved. 
• Planned maintenance: Normal maintenance activities that are happening on Azure or machine level (E.g., OS update). In general, there is no impact on the machine availability, expect exceptional cases when a reboot is required. For this scenarios, Maintenance-Redeploy can be used to trigger the restart in a convenable time window. 

Full article: https://vunvulearadu.blogspot.ro/2018/04/different-cases-of-azure-vm-reboots.html