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  • ALIF Consulting

Azure Compute Gallery

Updated: Oct 27

About Alif : Alif empowers Microsoft MSP-CSP partners to provide exceptional IT services to their clients to ensure that the partners reduce their costs and focus on their business. We provide white-labelled managed services for technologies like Microsoft Azure, Microsoft 365, Microsoft Dynamics 365, Microsoft Security, SharePoint, Power Platform, SQL, Azure DevOps and a lot more. Our headquarter is in Pune, India whereas we work with over 50 partners across the globe that trust us with their client delivery.


An Azure Compute Gallery helps you build structure and organization around your Azure resources, like images and applications. An Azure Compute Gallery provides:

  • Global replication.1

  • Versioning and grouping of resources for easier management.

  • Highly available resources with Zone Redundant Storage (ZRS) accounts in regions that support Availability Zones. ZRS offers better resilience against zonal failures.

  • Premium storage support (Premium_LRS).

  • Sharing to the community, across subscriptions, and between Active Directory (AD) tenants.

  • Scaling your deployments with resource replicas in each region.

  • With a gallery, you can share your resources to everyone, or limit sharing to different users, service principals, or AD groups within your organization. Resources can be replicated to multiple regions, for quicker scaling of your deployments.

  • 1 The Azure Compute Gallery service is not a global resource. For disaster recovery scenarios, it is a best practice is to have at least two galleries, in different regions.

Store an Image in Azure Compute Gallery

An image is a copy of either a full VM (including any attached data disks) or just the OS disk, depending on how it is created. When you create a VM from the image, a copy of the VHDs in the image are used to create the disks for the new VM. The image remains in storage and can be used over and over again to create new VMs.

If you have a large number of images that you need to maintain and would like to make them available throughout your company, you can use an Azure Compute Gallery as a repository.

When you use a gallery to store images, multiple resource types are created:


Resource

Description

Image source

This is a resource that can be used to create an image version in a gallery. An image source can be an existing Azure VM that is either generalized or specialized, a managed image, a snapshot, a VHD or an image version in another gallery.

Gallery

Like the Azure Marketplace, a gallery is a repository for managing and sharing images and other resources, but you control who has access.

Image definition

Image definitions are created within a gallery and they carry information about the image and any requirements for using it to create VMs. This includes whether the image is Windows or Linux, release notes, and minimum and maximum memory requirements. It is a definition of a type of image.

Image version

An image version is what you use to create a VM when using a gallery. You can have multiple versions of an image as needed for your environment. Like a managed image, when you use an image version to create a VM, the image version is used to create new disks for the VM. Image versions can be used multiple times.


VM apps

While you can create an image of a VM with apps pre-installed, you would need to update your image each time you have application changes. Separating your application installation from your VM images means there’s no need to publish a new image for every line of code change.


Regional Support

All public regions can be target regions, but certain regions require that customers go through a request process in order to gain access. To request that a subscription is added to the allow list for a region such as Australia Central or Australia Central 2, submit an access request

Limits

There are limits, per subscription, for deploying resources using Azure Compute Galleries:

  • 100 galleries, per subscription, per region

  • 1,000 image definitions, per subscription, per region

  • 10,000 image versions, per subscription, per region

  • 100 image version replicas, per subscription, per region however 50 replicas should be sufficient for most use cases

  • Any disk attached to the image must be less than or equal to 1TB in size


Scaling

Azure Compute Gallery allows you to specify the number of replicas you want to keep. This helps in multi-VM deployment scenarios as the VM deployments can be spread to different replicas reducing the chance of instance creation processing being throttled due to overloading of a single replica.

With Azure Compute Gallery, you can deploy up to a 1,000 VM instances in a virtual machine scale set. You can set a different replica count in each target region, based on the scale needs for the region. Since each replica is a copy of your resource, this helps scale your deployments linearly with each extra replica. While we understand no two resources or regions are the same, here's our general guideline on how to use replicas in a region:

· For every 20 VMs that you create concurrently, we recommend you keep one replica. For example, if you are creating 120 VMs concurrently using the same image in a region, we suggest you keep at least 6 replicas of your image.

· For each scale set you create concurrently, we recommend you keep one replica.

We always recommend that to over-provision the number of replicas due to factors like resource size, content and OS type.


High availability

Azure Zone Redundant Storage (ZRS) provides resilience against an Availability Zone failure in the region. With the general availability of Azure Compute Gallery, you can choose to store your images in ZRS accounts in regions with Availability Zones.

You can also choose the account type for each of the target regions. The default storage account type is Standard_LRS, but you can choose Standard_ZRS for regions with Availability Zones. For more information on regional availability of ZRS, see Data redundancy.


Replication

Azure Compute Gallery also allows you to replicate your resources to other Azure regions automatically. Each image version can be replicated to different regions depending on what makes sense for your organization. One example is to always replicate the latest image in multi-regions while all older image versions are only available in 1 region. This can help save on storage costs.

The regions that a resource is replicated to can be updated after creation time. The time it takes to replicate to different regions depends on the amount of data being copied and the number of regions the version is replicated to. This can take a few hours in some cases. While the replication is happening, you can view the status of replication per region. Once the image replication is complete in a region, you can then deploy a VM or scale-set using that resource in the region.


Sharing

There are three main ways to share images in an Azure Compute Gallery, depending on who you want to share with:


Share with:

Option

Role-based access control (RBAC) lets you share resources to specific people, groups, or service principals on a granular level.

​Direct shared gallery (preview) lets you share to everyone in a subscription or tenant.

Community gallery (preview) lets you share your entire gallery publicly, to all Azure users.

RBAC

As the Azure Compute Gallery, definition, and version are all resources, they can be shared using the built-in native Azure Roles-based Access Control (RBAC) roles. Using Azure RBAC roles you can share these resources to other users, service principals, and groups. You can even share access to individuals outside of the tenant they were created within. Once a user has access to the resource version, they can use it to deploy a VM or a Virtual Machine Scale Set. Here is the sharing matrix that helps understand what the user gets access to:


Shared with User

Azure Compute Gallery

Image Definition

Image version

​Azure Compute Gallery

Yes

Yes

Yes

Image Definition

No

Yes

Yes


We recommend sharing at the Gallery level for the best experience. We do not recommend sharing individual image versions. For more information about Azure RBAC

Shared directly to a tenant or subscription

Give specific subscriptions or tenants access to a direct shared Azure Compute Gallery. Sharing a gallery with tenants and subscriptions give them read-only access to your gallery.

Limitations

During the preview:

  • You can only share to subscriptions that are also in the preview.

  • You can only share to 30 subscriptions and 5 tenants.

  • A direct shared gallery cannot contain encrypted image versions. Encrypted images cannot be created within a gallery that is directly shared.

  • Only the owner of a subscription, or a user or service principal assigned to the Compute Gallery Sharing Admin role at the subscription or gallery level will be able to enable group-based sharing.

  • You need to create a new gallery, with the property sharingProfile.permissions set to Groups. When using the CLI to create a gallery, use the --permissions groups parameter. You can't use an existing gallery; the property can't currently be updated.

  • Billing

  • There is no extra charge for using the Azure Compute Gallery service. You will be charged for the following resources:

  • Storage costs of storing each replica. For images, the storage cost is charged as a snapshot and is based on the occupied size of the image version, the number of replicas of the image version and the number of regions the version is replicated to.

  • Network egress charges for replication of the first resource version from the source region to the replicated regions. Subsequent replicas are handled within the region, so there are no additional charges.


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