Monthly Archives: October 2013

Azure FAQ: IP Addresses and DNS

The Azure FAQWhen deploying an application or service to Windows Azure, a public IP address is assigned, making it easy to host a web server, API, or other services. Here are some of the more frequently asked questions asked about these IP addresses.

Q. Will my IP Address be Stable?

Short answer: Yes. Longer answer: For Cloud Services and Virtual Machines (but not Azure Web Sites) the IP address – once assigned – is stable, provided you do not remove the deployment. If you delete the deployment, your IP address goes back into the pool. For most production cloud applications it would very unusual to ever delete the deployment, so this is reasonable. Windows Azure supports in-place updates as well as the VIP Swap approach for Cloud Services, both of which always preserve the IP Address. Windows Azure Web Sites also has an IP Address-preserving swap feature.

Q. Can I map a “Naked” Domain to my Azure App or Service?

Short answer: Yes. The formal name for a so-called “naked” domain is a zone apex. But regardless of what we call it, it is simply a domain without any subdomain prefix. The address “devpartners.com” is a “naked” or “apex” domain, whereas  “www.devpartners.com” is not. And it is not just about counting periods in the domain: “amazon.co.jp” is also an apex domain. A DNS Address Record – or “A Record” for short – is used to configure an apex domain, and an A Record must be mapped to an IP Address. As noted in the question immediately above, you can have a stable IP address in Windows Azure, so therefore a stable A Record is possible, so therefore you can definitely map an apex record to your Windows Azure application or service. You can also use a DNS Canonical Name Record – or “CNAME” for short – to refer to a subdomain in your service. This is easy since, in addition to the stable IP address support mentioned above, Windows Azure provides a DNS name you can assign CNAMEs against. In Cloud Services (which includes Virtual Machines) this is of the form mycloudservice.cloudapp.net. [As opposed to Azure Web Sites which are of the form mywebsite.azurewebsites.net.]

Q. Is the IP Address Range Known?

Short answer: Yes. Longer answer: Microsoft publishes the IP Address Ranges used, organized by data center. So this published list of ranges can be consulted to review the possible IP address ranges. Specifically, the IP Address Ranges are documented here (http://msdn.microsoft.com/en-us/library/windowsazure/dn175718.aspx) and are expressed in Classless Inter-Domain Routing (CIDR) format. Be aware that as capacity increases and new data centers come on line, these ranges will evolve (I assume mostly the number of addresses will grow).

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