Using DNS in Azure Stack
Applies to: Azure Stack integrated systems and Azure Stack Development Kit
Azure Stack supports the following Azure DNS features:
- DNS hostname resolution
- Create and manage DNS zones and records using the API
Support for DNS hostname resolution
You can specify a DNS domain name label for public IP resources. Azure Stack uses domainnamelabel.location.cloudapp.azurestack.external for the label name and maps it to the public IP address in Azure Stack-managed DNS servers.
For example, if you create a public IP resource with contoso as a domain name label in the local Azure Stack location, the fully qualified domain name (FQDN) contoso.local.cloudapp.azurestack.external resolves to the public IP address of the resource. You can use this FQDN to create a custom domain CNAME record that points to the public IP address in Azure Stack.
To learn more about name resolution, see the DNS resolution article.
Each domain name label you create must be unique within its Azure Stack location.
The following screenshot shows the Create public IP address dialog for creating a public IP address using the portal:
You have a load balancer processing requests from a web application. Behind the load balancer is a web site running on one or more virtual machines. You can access the load-balanced web site using a DNS name, instead of an IP address.
Create and manage DNS zones and records using the API
You can create and manage DNS zones and records in Azure Stack.
Azure Stack provides a DNS service similar to Azure, using APIs that are consistent with the Azure DNS APIs. By hosting your domains in Azure Stack DNS, you can manage your DNS records using the same credentials, APIs, and tools. You can also use the same billing and support as your other Azure services.
The Azure Stack DNS infrastructure is more compact than Azure. The size and location of an Azure Stack deployment affects DNS scope, scale, and performance. This also means that performance, availability, global distribution, and high availability can vary from deployment to deployment.
Comparison with Azure DNS
DNS in Azure Stack is similar to DNS in Azure, but there are a few important exceptions:
Does not support AAAA records: Azure Stack does not support AAAA records because Azure Stack does not support IPv6 addresses. This is a key difference between DNS in Azure and Azure Stack.
Is not multi-tenant: The DNS Service in Azure Stack is not multi-tenant. Each tenant cannot create the same DNS zone. Only the first subscription that attempts to create the zone succeeds, and subsequent requests fail. This is another key difference between Azure and Azure Stack DNS.
Tags, metadata, and Etags: There are minor differences in how Azure Stack handles tags, metadata, Etags, and limits.
To learn more about Azure DNS, see DNS zones and records.
Azure Stack DNS supports using Azure Resource Manager tags on DNS zone resources. It does not support tags on DNS record sets, although as an alternative, metadata is supported on DNS record sets, as explained in the next section.
As an alternative to record set tags, Azure Stack DNS supports annotating record sets using metadata. Similar to tags, metadata enables you to associate name-value pairs with each record set. For example, this can be useful to record the purpose of each record set. Unlike tags, you cannot use metadata to provide a filtered view of your Azure bill, and metadata cannot be specified in an Azure Resource Manager policy.
Suppose two people or two processes try to modify a DNS record at the same time. Which one wins? And does the winner know that they've overwritten changes created by someone else?
Azure Stack DNS uses Etags to safely handle concurrent changes to the same resource. Etags are different from Azure Resource Manager Tags. Each DNS resource (zone or record set) has an Etag associated with it. When a resource is retrieved, its Etag is also retrieved. When updating a resource, you can choose to pass back the Etag so Azure Stack DNS can verify that the Etag on the server matches. Since each update to a resource results in the Etag being regenerated, an Etag mismatch indicates a concurrent change has occurred. Etags can also be used when creating a new resource to ensure that the resource does not already exist.
By default, Azure Stack DNS PowerShell cmdlets use Etags to block concurrent changes to zones and record sets. You can use the optional
-Overwrite switch to suppress Etag checks, which causes any concurrent changes that have occurred to be overwritten.
At the level of the Azure Stack DNS REST API, Etags are specified using HTTP headers. Their behavior is described in the following table:
|None||PUT always succeeds (no Etag checks)|
|If-match||PUT only succeeds if resource exists and Etag matches|
|If-match *||PUT only succeeds if resource exists|
|If-none-match *||PUT only succeeds if resource does not exist|
The following default limits apply when using Azure Stack DNS:
|Zones per subscription||100|
|Record sets per zone||5000|
|Records per record set||20|
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