The Office 365 CDN (Content Delivery Networks) may be activated to host SharePoint Online files in a more globally accessible manner. The general premise behind this is that static assets can be served to users from a location more local to them than the data centre in which the Office 365 tenant is located.

I won’t go into the real benefits of this beyond to say that my limited testing at this point leads me to believe that the performance impact of using a CDN will be negligible for the vast majority of users/organisations. This is because the volume of data which can be served via the CDN is not a significant proportion of the data impacting page load speed.

Regardless, the documentation around how to get started with the Office 365 CDN is decent. A good place to start is this link.

A couple of gotchas I’ve noticed

• Fetching an image rendition using the width query string parameter does NOT correctly return the image rendition as configured. It simply scales the image to the specified width (i.e. no cropping or positioning is performed).
• If all users are located in the same region as the Office 365 tenant, turning on the CDN may reduce performance due to CDN priming (replication of files to the CDN) and will complicate updates to files which are replicated (e.g. JavaScript in the Style Library).
• Search web parts must be configured for ‘Loading Behaviour’ – ‘Sync option: Issue query from the server’ in order for the auto rewrite of CDN hosted files to occur. This is true for display templates as well as the value of the PublishingImage managed property

Office 365 CDN PowerShell Samples

I’ve got some sample PowerShell below showing how to activate the Office 365 CDN (there’s private and public, you can use either or both) and associate origins with it (an origin is a document library which will be replicated to the CDN).

I’ve also got a simple sample of how to remove all origins as there is not a single cmdlet for this. It is worth noting that although an enabled CDN with no origins is functionally identical to a disabled CDN (i.e. no files are being replicated) they are not the same from a configuration perspective.

Please note that these are just sample scripts and have not been parameterised as you may require.

Calling the PowerShell functions:

$cdnType = "Private" # Private or Public
$serverRelSiteCollectionUrl = "/sites/mysite" # site collection URL or * for all site collections

Authenticate-PowerShell

Set-CdnConfiguration $serverRelSiteCollectionUrl $cdnType

#Remove-CdnConfiguration $cdnType # This removes all origins but the CDN is still enabled
#Set-SPOTenantCdnEnabled -CdnType $cdnType -Enable $false # This disables the CDN

The PowerShell functions:

Function Authenticate-PowerShell() {
	[string]$tenantUrl = "https://TENANT-admin.sharepoint.com"
	[string]$adminUsername = "USER@TENANT.onmicrosoft.com"
	[string]$adminPassword = "PASSWORD"

	# Ensure module is loaded
	if ((Get-Module Microsoft.Online.SharePoint.PowerShell).Count -eq 0) {
		Import-Module Microsoft.Online.SharePoint.PowerShell -DisableNameChecking
	}

	$secureAdminPassword = $(convertto-securestring $adminPassword -asplaintext -force)
	$cred = New-Object -TypeName System.Management.Automation.PSCredential -argumentlist $adminUsername, $secureAdminPassword
	Connect-SPOService -Url $tenantUrl -credential $cred
}

Function Set-CdnConfiguration($serverRelSiteCollectionUrl, $cdnType){
    #LogWaiting "Configuring CDN"
    #LogInfo ""

    $fileTypes = "GIF,ICO,JPEG,JPG,JS,PNG,CSS,EOT,SCG,TTF,WOFF"
    $cdnOrigins = @(
        "$serverRelSiteCollectionUrl/_catalogs/masterpage", 
        "$serverRelSiteCollectionUrl/style library",  
        "$serverRelSiteCollectionUrl/sitecollectionimages",
        "$serverRelSiteCollectionUrl/publishingimages"#,
        #"$serverRelSiteCollectionUrl/news/publishingimages"
    )

    # Enable cdn WITHOUT default origins
    $supressOutput = Set-SPOTenantCdnEnabled -CdnType $cdnType -Enable $true -NoDefaultOrigins -Confirm:$false

    # Configure cdn origins (incl ensure default origins)
    Ensure-CdnOrigin $cdnType $cdnOrigins

    # Extend list of file types
    $supressOutput = Set-SPOTenantCdnPolicy -CdnType $cdnType -PolicyType IncludeFileExtensions -PolicyValue $fileTypes

    #LogSuccess "done"

    # Print status
    Get-SPOTenantCdnOrigins -CdnType $cdnType
}

Function Ensure-CdnOrigin($cdnType, $originUrls){
  $originUrls | ForEach {
    $oUrl = $_
    try {
      #LogWaiting "Adding origin: $oUrl"
      $supressOutput = Add-SPOTenantCdnOrigin -CdnType $cdnType -OriginUrl $oUrl -Confirm:$false
    }
    catch {
      if($Error[0].Exception.ToString().Contains("The library is already registered as a CDN origin")) {
        # aleady present, do nothing
      }
      else {
        #LogError $Error[0]
        Exit
      }
    }
    #LogSuccess "done"
  }
}

Function Remove-CdnConfiguration($cdnType){
	(Get-SPOTenantCdnOrigins -CdnType $cdnType)	| ForEach { $_ | ForEach { $supress = Remove-SPOTenantCdnOrigin -CdnType $cdnType -OriginUrl $_ -Confirm:$false }}
}

Paul.