Azure Dedicated Host is a service that provides physical servers that are able to host one or more virtual machines and are dedicated to one Azure subscription. Dedicated hosts are the same physical servers used in our data centers, provided as a resource. You can provision dedicated hosts within a region, availability zone, and fault domain. Then, you can place VMs directly into your provisioned hosts in whatever configuration best meets your needs.
Benefits
Reserving the entire host provides the following benefits:
Hardware isolation at the physical server level. No other VMs will be placed on your hosts. Dedicated hosts are deployed in the same data centers and share the same network and underlying storage infrastructure as other, non-isolated hosts.
Control over maintenance events initiated by the Azure platform. While the majority of maintenance events have little to no impact on your virtual machines, there are some sensitive workloads where each second of pause can have an impact. With dedicated hosts, you can opt into a maintenance window to reduce the impact to your service.
With the Azure Hybrid benefit, you can bring your own licenses for Windows and SQL to Azure. Using the hybrid benefits provides you with additional benefits.
Groups, hosts, and VMs
A host group is a resource that represents a collection of dedicated hosts. You create a host group in a region and an availability zone and add hosts to it.
A host is a resource mapped to a physical server in an Azure data center. The physical server is allocated when the host is created. A host is created within a host group. A host has a SKU describing which VM sizes can be created. Each host can host multiple VMs of different sizes as long as they are from the same size series.
High Availability considerations
For high availability, you should deploy multiple VMs, spread across multiple hosts (minimum of 2). With Azure Dedicated Hosts, you have several options to provision your infrastructure to shape your fault isolation boundaries.
Use Availability Zones for fault isolation
Availability zones are unique physical locations within an Azure region. Each zone is made up of one or more data centres equipped with independent power, cooling, and networking. A host group is created in a single availability zone. Once created, all hosts will be placed within that zone. To achieve high availability across zones, you need to create multiple host groups (one per zone) and spread your hosts accordingly.
If you assign a host group to an availability zone, all VMs created on that host must be created in the same zone.
Use Fault Domains for fault isolation
A host can be created in a specific fault domain. Just like VM in a scale set or availability set, hosts in different fault domains will be placed on different physical racks in the data center. When you create a host group, you are required to specify the fault domain count. When creating hosts within the host group, you assign a fault domain for each host. The VMs do not require any fault domain assignment.
Fault domains are not the same as colocation. Having the same fault domain for two hosts does not mean they are in proximity to each other.
Fault domains are scoped to the host group. You should not make any assumption on anti-affinity between two host groups (unless they are in different availability zones).
VMs deployed to hosts with different fault domains will have their underlying managed disk services on multiple storage stamps to increase fault isolation protection.
Using Availability Zones and Fault Domains
You can use both capabilities together to achieve even more fault isolation. In this case, you will specify the availability zone and fault domain count for each host group, assign a fault domain to each of your hosts in the group, and assign an availability zone to each of your VMs
The Resource Manager sample template uses zones and fault domains to spread hosts for maximum resiliency in a region.
Manual vs. automatic placement
When creating a VM in Azure, you can select which dedicated host to use. You can also use the option to automatically place your VMs on existing hosts within a host group.
When creating a new host group, make sure the automatic VM placement setting is selected. When creating your VM, select the host group and let Azure pick the best host for your VM.
Host groups that are enabled for automatic placement do not require all the VMs to be automatically placed. You will still be able to explicitly pick a host, even when automatic placement is selected for the host group.
Visibility and control
Azure Dedicated Hosts can assist in fulfilling organizations' compliance requirements regarding physical security, data integrity, and monitoring by enabling the deployment of Azure VMs on specific, dedicated physical servers. This service also caters to the needs of IT organizations that require host-level isolation.
Azure Dedicated Hosts offer visibility into the server infrastructure supporting your Azure Virtual Machines. They grant you more control over:
- The underlying hardware infrastructure (host type)
- Processor brand, capabilities, and more
- Number of cores
- Type and size of the Azure Virtual Machines for deployment
You can deploy different sizes of Azure Virtual Machines from the same virtual machine series on a single host.
By using an Azure Dedicated Host, you can manage all host-level platform maintenance initiated by Azure, such as host OS updates. With an Azure Dedicated Host, you have the flexibility to delay host maintenance operations and perform them within a specified maintenance window of 35 days. During this self-maintenance window, you have the ability to carry out maintenance on your hosts at your convenience, thus gaining complete control over the sequence and pace of the maintenance process.
Licensing cost savings
Microsoft are now providing Azure Hybrid Benefit for Windows Server and SQL Server on Azure Dedicated Hosts, which makes it the most economical dedicated cloud service for Microsoft workloads.
Azure Hybrid Benefit enables you to utilize existing licenses for Windows Server and SQL Server with Software Assurance or qualifying subscription licenses to pay a lower rate for Azure services.
We are also broadening the Azure Hybrid Benefit to allow you to make use of unrestricted virtualization for Windows Server and SQL Server with Azure Dedicated Hosts. Customers with Windows Server Datacenter licenses and Software Assurance can utilize unlimited virtualization rights in Azure Dedicated Hosts, meaning they can deploy as many Windows Server virtual machines as they like on the host, limited only by the physical capacity of the underlying server. Similarly, customers with SQL Server Enterprise Edition licenses and Software Assurance can make use of unlimited virtualization rights for SQL Server on their Azure Dedicated Hosts.
Just like with other Azure services, customers will receive free Extended Security Updates for Windows Server 2008/R2 and SQL Server 2008/R2 on Azure Dedicated Hosts.
Azure Dedicated Hosts allow you to use other existing software licenses, such as SUSE or RedHat Linux. Contact your vendors for detailed license terms.
With the introduction of Azure Dedicated Hosts, we are updating the outsourcing terms for Microsoft on-premises licenses to clarify the difference between on-premises/traditional outsourcing and cloud services.
Limitations
Known issues and limitations when using automatic VM placement:
You will not be able to redeploy your VM.
You will not be able to use DCv2, Lsv2, NVasv4, NVsv3, Msv2, or M-series VMs with dedicated hosts
Pricing
Users are charged per dedicated host, regardless how many VMs are deployed. In your monthly statement you will see a new billable resource type of hosts. The VMs on a dedicated host will still be shown in your statement but will carry a price of 0.
The host price is set based on VM family, type (hardware size), and region. A host price is relative to the largest VM size supported on the host.
Software licensing, storage and network usage are billed separately from the host and VMs. There is no change to those billable items.
Sizes and hardware generations
A SKU is defined for a host, and it represents the VM size series and type. You can mix multiple VMs of different sizes within a single host as long as they are of the same size series.
The type is the hardware generation. Different hardware types for the same VM series will be from different CPU vendors and have different CPU generations and number of cores.
Host life cycle
Azure monitors and manages the health status of your hosts. The following states will be returned when you query your host:
Health State | Description |
Host Available | There are no known issues with your host. |
Host Under Investigation | We’re looking into some issues with the host. This is a transitional state required for Azure to try to identify the scope and root cause of the issue identified. Virtual machines running on the host may be impacted. |
Host Pending Deallocate | Azure can’t restore the host back to a healthy state and ask you to redeploy your virtual machines out of this host. If autoReplaceOnFailure is enabled, your virtual machines are service healed to healthy hardware. Otherwise, your virtual machine may be running on a host that is about to fail. |
Host deallocated | All virtual machines have been removed from the host. You are no longer being charged for this host since the hardware was taken out of rotation. |
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