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WAC? OOS? OOS and WAC?

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Previous versions of Exchange used Web-ready Document Viewing for the built-in preview of Office and PDF documents. Exchange 2013 also had the ability to make the experience richer by configuring it to use an Office Web Apps Server. Now Exchange 2016 is here, we are leveraging the power of Office Online Server (OOS), which is the vNext of Office Web Apps Server (also known as WAC).  Now, those of you with a keen eye may have spotted that Office Online Server is only available in Preview at the moment, which means it is not supported in production environments.  So this leaves us a bit stuck when it comes to an Exchange 2016 deployment where we do not want users to have to download attachments to view them.  Chances are, if you are using OWA, you may not be somewhere where you have a full Office client to be able to open the downloaded document. 

 So what can you do? 

 In short, nothing. You will have to wait until OOS reaches General Availability. But hey, every cloud has a silver lining: it will give you time to properly plan your new Exchange 2016 environment!

 

Now, there is another part of the WAC/OOS story.  Namely, co-existence in a 2013 environment. First, let's recap how Exchange 2013 uses WAC.  WAC is configured at Organization level for 2013. If you've already got a WAC server in place (for Lync/SfB), the setup is nice and simple:

 

Set-OrganizationConfig -WACDiscoveryEndPoint https://Server1/hosting/discovery

 If only everything was that simple.

 Now, in Exchange 2016 things are a little different. We have two different places where we can configure our endpoint: at the organization level, and at the Mailbox server level. Where you configure the endpoint depends on the size of your organization and the location of your servers and users.

 

Organization - There are a couple of reasons why you might configure the Office Online Server Preview endpoint at the organization level:

  • Single-server or single-location deployment You can configure the endpoint at the organization level if all of your Exchange 2016 Mailbox servers are in the same location and you don't plan on having geographically distributed Office Online Server Preview servers.
  • Fallback for large deployments You can configure an endpoint at the organization level as a fallback if the endpoint configured on a Mailbox server isn't available. If an Office Web Apps server isn't available, the client will try to connect to the endpoint configured at the organization level.

 

Mailbox server - If you want to distribute client requests between two or more Office Online Server Preview servers, if you want to geographically distribute Office Online Server Preview servers, or if you have Exchange 2013 in your organization, configure the endpoints at the Exchange 2016 Mailbox server level. When you configure an endpoint at the server level, mailboxes located on that server will send requests to the configured Office Online Server Preview server.

Before we move on, take in the following:

Exchange 2013 uses Office Web Apps Server and does not support Office Online Server.

Exchange 2016 uses Offline Online Server and does not support Office Web Apps Server.

Exchange 2013 was an Organization level configuration.

Let's think about this.. If I have configured WAC for Exchange 2013 and I want to introduce Exchange 2016 into my environment, I am going to have a problem. Exchange 2016 does not work with the settings configured at Organization level because they are pointing to the WAC server, which is not supported.  I cannot change the Organization-level settings to OOS because Exchange 2013 servers do not support it.

So we're stuck, right?  Well, not quite.  Remember we can now configure our endpoint at server level in Exchange 2016! So that's what we do:

 

Set-MailboxServer ShinyNew2016Server -WacDiscoveryEndpoint "https://oos.internal.contoso.com/hosting/discovery"

 

Easy, right?  Well, yes, but we need to remember one small point about how Exchange 2016 works. It was mentioned above, but let's say it again here and highlight the important bit. "You can configure an endpoint at the organization level as a fallback if the endpoint configured on a Mailbox server isn't available. If an Office Web Apps server isn't available, the client will try to connect to the endpoint configured at the organization level."

Do you spot the potential issue here? What if my OOS server goes down?  Or what about when we need to patch it? That's right, we would fall back to the Organization-level setting, which has been configured with a WAC endpoint for our Exchange 2013 deployment. Not supported, remember?

Hmm.. So what's the Microsoft guidance for this situation then?

You will need to make sure that you configure your endpoint at server level on your Exchange 2016 servers, and that the endpoints are highly available. By this, we mean you would need to deploy at least two OOS servers in a farm configuration to make sure that, should one go down, you will still have an OOS endpoint available.  This will make fall-back to the WAC server configured at Organization level no longer a possibility and keep everything working in a supported configuration.