How Microsoft helps you NOT break your Windows Azure Application: Storage Services Versioning

BuckWoody — Tue, 06 Dec 2011 14:42:57 GMT

One of the advantages of using Windows Azure to run your code is that you don’t have to constantly manage upgrades on your platform. While that’s a big advantage indeed, it immediately brings up the question - how do the upgrades happen? Microsoft upgrades the Azure platform in periodic increments, and the components that are affected are documented.

This brings up another question - upgrades mean change, and change can sometimes alter the way you might implement a feature. What if you have taken a dependency on some feature in your code that has been altered by an upgrade? Windows Azure does have an Application Lifecycle Management (ALM) Process, which I’ll reference at the end of this post. But beyond that, there are some features we’ve put into place that will help you manage many of these changes. One of those is being able to set the version of storage features you would like your code to use.

Windows Azure is made up of three main component areas: Computing, Storage and a group of features called the Application Fabric. You can use these components together or separately, depending on what you would like your application to do. In this post I’ll deal with the version control in the storage subsystem - in other posts I’ll explain how to track and in some cases control the versions of the other components you work with.

When you send a request to a Windows Azure resource, you’re actually using a REST call. That’s a three-part call to the system that has a request (called a URI), a header, and a body of code you want to send. So a typical call, such as to a table, might look like this example, which changes the properties of a Blob:

URI:
PUT http://myaccount.table.core.windows.net/?restype=service&comp=properties HTTP/1.1

Header:
x-ms-version: 2011-08-18
x-ms-date: Tue, 30 Aug 2011 04:28:19 GMT
Authorization: SharedKey
myaccount:Z1lTLDwtq5o1UYQluucdsXk6/iB7YxEu0m6VofAEkUE=
Host: myaccount.table.core.windows.net

Body:
<?xml version="1.0" encoding="utf-8"?>
<StorageServiceProperties>
    <Logging>
        <Version>1.0</Version>
        <Delete>true</Delete>
        <Read>false</Read>
        <Write>true</Write>
        <RetentionPolicy>
            <Enabled>true</Enabled>
            <Days>7</Days>
        </RetentionPolicy>
    </Logging>
    <Metrics>
        <Version>1.0</Version>
        <Enabled>true</Enabled>
        <IncludeAPIs>false</IncludeAPIs>
        <RetentionPolicy>
            <Enabled>true</Enabled>
            <Days>7</Days>
        </RetentionPolicy>
    </Metrics>
</StorageServiceProperties>

(Source of this code)

You can see that I’ve highlighted a portion of the header block - that’s where you set the version of the Storage Services you would like to use. You can find a list of the features introduced in each version here. It’s not a requirement of adding that element to the header, but it’s best practices to do so.

You don’t have to use REST calls directly, however. It’s more common to use the API in the Software Development Kit to just change the property in your IDE environment - the setting you’re looking for there is the Set Storage Service Properties call.

Interestingly, rather than a breaking change you might run into an unexpected behavior if you are not aware of these parameters. In some code I recently reviewed a newer feature from the storage system failed when it was called. On inspection I found that the developer had used an older codeblock from a previous version of the storage system - he was not aware you can set the version of storage in the call. We changed the header to the latest version, and everything worked as expected.

References:

The Storage Services Versioning and the changes for each version:

http://msdn.microsoft.com/en-us/library/windowsazure/dd894041.aspx

Windows Azure Application Lifecycle Management:

http://msdn.microsoft.com/en-us/library/ff803362.aspx

http://channel9.msdn.com/posts/Windows-Azure-Jump-Start-03-Windows-Azure-Lifecycle-Part-1

http://channel9.msdn.com/Events/TechEd/Australia/Tech-Ed-Australia-2011/COS201

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How Microsoft helps you NOT break your Windows Azure Application: Storage Services Versioning