Saturday, October 6, 2018

Exchange 2016 Publishing REST/OData For API With Kemp Load Balancer

Our company is designing an app for users to have an all-in-one-do-everything portal that will incorporate a mail client that connects to our on-prem Exchange. The app utilizes the Outlook Mail REST API to grab messages from the user's mailbox.

**Note** Office365 supports REST by default; it wasn't until Exchange 2016 CU3 that it was available for on-prem (go figure).

You can find the details here:


If you're running on-prem, you should be patched up way beyond CU3, right?

The issue is: REST API is enabled on Exchange 2016 CU3+ but if you run a load balancer, like Kemp's super-awesome Load Master, the API won't be published out of the box.

By default, the Kemp Exchange templates don't enable Exchange API to be published. As a workaround, you can enable the "default" content rule on your SubVSs, but some IT security departments won't like that, because it's a blanket rule.

What we'll do instead, is create a Custom Content Rule, and apply it to our OWA SubVSs ('Sub-Virtual Services), which will allow the API to be published.

Create The Rule:

In your Load Master WUI, go to Rules & Checking > Content Rules > Create New Rule:

Kemp Add New Rule 1

Give it a name like "REST_API"

Rule type: leave as default (Content Matching)

Match type: leave as default (Regular Expression)

Match string: type in the following:


Tick Ignore Case

Click Create Rule:

Kemp Add New Rule 2

Your new rule will be listed:

Kemp Rule Created

Adding The New Rule:

Next, we'll add our new content rule to our OWA SubVSs

Navigate to Virtual Services > View/Modify Services

Click Modify next to your Internal Service:

Kemp Modify VSs 1

**Note** You can modify your external service if you want; it would just depend on your security requirements. For instance, our IT Security Department doesn't understand Exchange and therefore won't allow me to publish OWA externally, so I can only publish the API internally as well.

Expand SubVSs, and click the Rules button next to OWA:

Kemp Modify VSs 2

In the drop-down, select our new "API_REST" rule and click Add:

Kemp Add Rule 1
Kemp Add Rule 2
You'll now see the API_REST rule listed for the OWA rule set:
Kemp Rule Added to VSs
Testing The New Rule:
In a web browser navigate to your Exchange namespace with the API URL at the end, like so:
You will be presented with a Save/Open JSON prompt:
Mailbox json prompt
Open in Notepad, and you'll see your messages in your mailbox:
Mailbox API Messages Content
Now your on-premises Exchange API REST/OData is published, and the app (or whatever needs that service) can hit it!

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