Azure VM Availability

See the Regions and availability page at Microsoft.

Maintenance and Downtime

There are three scenarios that can lead to virtual machine in Azure being impacted.

• Unplanned Hardware Maintenance - Occurs when the Azure platform predicts that the hardware or a platform component is about to fail. This will issue and hardware maintenance event. Azure uses Live Migration technology to move the VM to a healthy physical machine. Memory, open files and network connections are still active after a Live Migration. The performance may get reduced before and after the migration.
• Unexpected Downtime - Is when the hardware or infrastructure for the VM fails unexpectedly. This can include network, disk or rack (power) failures. When the Azure platform detects a failure the VM will migrate to a healthy physical machine. During the healing procedure the VM will be down and do a new boot. In some cases you will lose the temporary disk.
• Planned Maintenance - Are periodic updates made by Microsoft to the underlying platform. Most updates are without any impact on the VM. There are various maintenance scenarios, some will pause a machine, reboot a machine or perform a live migration.

Microsoft does not automatically update your VMs OS or software. The underlying software host and hardware are periodically patched. Also see the Azure VM Availability article.

Availability Sets

An Availability Set is a logical group of virtual servers to eliminate a single point of failure or upgraded at the same time. The VM machines in a availability set should be identical and perform the same functionality.

An Availability Set consists of the following two:

• Fault domains - VMs placed in Fault domain will ensure they will be spread across different physical servers, compute racks, storage units, and network switches.
• Update domains - If VMs are separated by an Update domain will not get updated at the same time. During planned maintenance, only one update domain is rebooted.

Keep the following rules in mind:

• Configure multiple virtual machines in an Availability Set.
• Configure Each Application tier in a separate Availability Set.
• Combine Load Balancers with Availability Sets.
• Use managed Disks with Availability Sets.

Availability zones

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Service Level Agreements

The Azure SLA is based on the availability.

• For two VMs in a availability set Microsoft will guarantee a connectivity of at least 99.95% of the time.
• For Two VMs or more deployed across two or more Availability Zones in the same Azure region, Microsoft will guarantee a connectivity of at least 99.99% of the time.
• For any Single Instance Virtual Machine using premium storage for all disks, we guarantee you will have Virtual Machine Connectivity of at least 99.9%.

See the Azure SLA for more details and return of credits.