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Office 365 Public Content Delivery Network Comes to SharePoint Sites

Office 365 Public Content Delivery Network (CD), which is free for Office 365 tenancies, aims to speed up the performance of SharePoint Online sites.

Microsoft announced the "general availability" of the Office 365 Public CDN on Friday, following a preview release back in September. The CDN is a means of hosting resources to speed up content delivery for end users, based on their locations. For Office 365 services, these CDNs are typically hosted on Microsoft Azure datacenter infrastructure or on Akamai's datacenters. The content that gets stored in a Public CDN typically includes generic items, such as files, images and scripts.

Private CDNs also are available. Today, Microsoft also announced a preview of its Office 365 Private CDN with a new "Publishing Feature Auto-Rewrite integration" capability, which is just available now for Office 365 tenancies signed up to be on the "first-release" Office 365 update cycle. The first-release branch is typically used for testing purposes.  

Organizations might use the Office 365 Public or Private CDNs to support their intranet portals, which typically use custom JavaScript, Cascading Style Sheets and images. CDN use can improve latency issues for those portals.

"The Public/Private CDN feature will help improve the latency of these [intranet] sites because the CDN assets are geo-distributed so they are cached closer to the user and the CDN domain supports the HTTP/2 protocol which provides parallel downloading," explained Vesa Juvonen, a senior program manager for OneDrive-SharePoint engineering at Microsoft, in the announcement. "This means we are no longer limited to 6 ports per domain like with HTTP/1.1."

It's possible to use the Office 365 Public CDN and the Office 365 Private CDN at the same time, which is "a common scenario" according to Juvonen. The Private CDN might be used to house author content images, he added.

A description of public vs. private Office 365 CDNs can be found in Microsoft's "Content Delivery Networks" support document. The difference has to do with token use for security purposes, but private CDNs also can be distinguished by ownership, according to the document:

Private CDNs are owned and operated by a single company, and only that company's applications and services can use it. Public CDNs are run by companies who lease usage to multiple companies. Depending on where you're located, it might be most efficient for Office 365 to download generic images for you from a CDN that Office 365 owns and runs, a public CDN, or a combination of the two.

Microsoft includes access to the CDNs at no extra cost to Office 365 subscribers. However, IT pros have to enable the access. They'll have to run a few SharePoint Online Management PowerShell cmdlets ("commandlets"), as described in Microsoft's announcement, to turn on CDN support for SharePoint Online sites. A requirement for using those cmdlets is to have the latest version of the SharePoint Online Management Shell installed.

One benefit of using the Office 365 Public CDN is that it can be used to host "SharePoint Framework client-side web part files," Juvonen noted. However, it's not possible to host those WebPart files on the Office 365 Private CDN right now, he added.

Microsoft's announcement explained that the Office 365 Public CDN uses a static URL for the housed content. In contrast, the Office 365 Private CDN uses URLs that have been "dynamically generated by SharePoint Online" and are associated with tokens to limit access.

Microsoft is planning to release a new tutorial in "upcoming days" that will describe how to host WebPart files using the Office 365 CDN, Juvonen promised.

About the Author

Kurt Mackie is senior news producer for the 1105 Enterprise Computing Group.

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