This post was originally published here

Recently I was asked by a client: how do I deploy an API App or a Logic App to a Virtual Network (VNet)?

If you’ve ever used BizTalk Services (MABS) then you’ll know one of the biggest limitations with MABS was that it didn’t support VNets: a lot of companies create VNets, and hook them up to their on-premises network, so that their Azure environment becomes a secure extension of their on-premises network.

VNets can also be set to only allow trusted connections from external users through the use of firewalls, network appliances or network configuration.

At the date of writing, there is currently no support for running Logic Apps in a VNet (yet, but watch this space) but there is for the other parts of Azure App Service (AAS): the problem is solved through the use of App Service Environments (ASEs).

Introduction to App Service Environments (ASEs)

ASEs have been around for a while (they previewed in April 2015, just after AAS went into preview, and Logic Apps/API Apps were announced) but there hasn’t been too much coverage of them, hence my client’s question. ASEs are part of Azure App Service.

An ASE is effectively a private deployment of all the VMs and services needed to run your AAS apps. Instead of running on either shared VMs (Free and Standard Plans) or dedicated VMs in the public portions of your subscription, ASEs give an entire deployment of everything needed to host AAS apps but in a VNet – with the added benefit that you get a lot of control over the scale up/scale out options.

When you create an ASE it *has* to exist in a VNet: you can’t create one outside of a VNet. The VNet is either created for you (with default values) or you can select a pre-existing VNet when you create the ASE.

Configuration of an ASE can look a bit daunting, but it becomes easier if you think of it as your own set of virtual servers, with a set of front-end servers and 3 groups of processing servers running in your VNet. All of the supported AAS goodies (web apps, api apps, etc.) are deployed onto these servers, and you get to control the number of servers available to handle load.

Servers are grouped into either Front-End, Worker Pool 1, Worker Pool 2, or Worker Pool 3.

You can set the number of instances per group – so the default is for a front-end group with 2 servers, and single worker pool group with 2 servers, plus one allocated IP address. Note that these aren’t the actual number of instances assigned to your API App (or Web or Mobile) when you deploy it – this is the just the number of instances that exist in the group that can be used. When you deploy your AAS app, you choose which group it uses.

In ASE terminology, each group is known as a pool, and the servers as instances: so if you want two servers running on a worker process group, you’d have two worker pool instances running in your worker pool.

Technically, each pool instance is a compute resource: you can have a maximum of 55 compute resources spread across your front-end pool and worker pools, and a maximum of 10 IP addresses e.g. 5 front-end instances, and 2 worker pools each with 25 instances (the Azure portal has some pretty nifty code in it which adjusts the ratio on the sliders as you adjust the numbers!).

ASEs are part of the Premium tier, which means they can get expensive: even at the default settings the per hour cost is reasonably high, even with nothing running in the ASE and no storage. As you add more instances, or more pools, the price per day increases.

How to create an ASE

The option to create an ASE can be found under Web + Mobile, right under the Logic App item, when you click New in the Azure portal:

When you select App Service Environment you’ll be given the option to give it a name, select or create the Resource Group the ASE will belong to, select or create a VNet, and choose scaling options:

On this screen you specify:

  1. Your ASE name – note that your ASE is given a name on the domain – you’ll have to make your ASE name unique amongst all other ASE names.

  2. The subscription your ASE will be created in.

  3. The Resource group your ASE will belong to (this can be a new one or an existing one).

  4. The Virtual Network/Location for your ASE (by default a new VNet is created for you, but you either choose an existing VNet, or change the options of the default VNet that is created).

  5. Scalability i.e. how many pools and pool instances you want.

Note the information box that indicates it will take a minimum of 2 hours to create your ASE – this is accurate, as I’ve found from experience.

Selecting the Scale option shows this screen:

Here you can specify what pricing tier you want to use for your pools (each pool can be set to a different pricing tier, although the Front End Pool must be at P2 at minimum).

After this, you can set the number of instances in each pool, and how many IP Addresses you need.

If you select one of the tier options for a pool, you’ll see a screen like this:

What this lets you do is set the number of cores available for each of your instances i.e. the number of cores for each of your virtual servers.

Looking at those numbers, and knowing the defaults for an ASE, you can see that the default settings will cost you a minimum of £272.70/month (about US$400/mo), and that’s without any additional storage or traffic charges.

Note: ASEs can be expensive, but they’re in the Premium tier for a reason: they’re designed to handle very high load (if necessary) for customers that need an isolated environment within a virtual network e.g. 50 8-core virtual servers. Plus, there’s one thing you can do with ASEs that is difficult to do otherwise: you can provide automated geographic redundancy (more on this later).

After you click the Create button, Azure goes off and creates your ASE – this will take a minimum of 2 hours.

How to deploy an API App to an ASE

OK, so now you have your shiny new ASE – how do we deploy an API App to it? Well this is the really easy part: Your ASE will show up in your list of Locations when you create your API App (as long as you select the correct subscription).

For example, if I create an instance of the BizTalk Flat File Encoder, my location happens to automatically default to the ASE I created earlier:

Note that we now have a new option available – Worker Pool Size. This lets us select the worker pool to use with the API App (remember setting up Worker Pools when you created the ASE?). You use this to select which worker pool you want to use (i.e. Worker Pool 1, Worker Pool 2, etc.).

Also, I note that you can select an existing resource group, or create a new one, although the facility to choose an existing one wasn’t working correctly at the time of this post.

If we select the Location option, we can see that the ASE appears in the list of locations:

Benefits of deploying API Apps or Logic Apps to an ASE

The two main benefits of an ASE are these:

  1. Ability to deploy to a VNet.

  2. Ability to scale worker instances beyond that which is available in AAS outside on an ASE.

The VNet argument should be easy: if you have an on-premises network which you are connecting to Azure (either by VPN or ExpressRoute or similar), then an ASE allows you to both access your AAS apps from your on-premises servers as well as allowing your AAS apps to access on-premises server – no hybrid connectivity or service bus relay needed! Plus you can use network security groups to restrict traffic access to your AAS apps on an IP level.

The ability to scale is essential if your workload is going to go beyond the capabilities offered by vanilla AAS: up to 55 dedicated compute resources, each with up to 8 cores. The ability for your ASE to autoscale as demand requires it is also essential for enterprise apps.

Why can’t we add Logic Apps to an ASE?

When ASEs first came out, there was a bit of confusion about whether Logic Apps and API apps were supported: the initial announcements indicated they were, but there appeared to be no way of adding API Apps and Logic Apps to ASEs. That has changed, with the official guidance now updated to indicate that Web Apps, Mobile Apps, and API apps are all supported, but not Logic Apps.

Given that Logic Apps are still in preview, this is perhaps not surprising – and I wouldn’t be surprised if we find Logic Apps gaining ASE support before the GA of Logic Apps next year (perhaps even during one of the earlier updates mentioned in the Logic Apps Roadmap).

Further Resources

There’s a wealth of information from Microsoft on ASEs – here’s a partial list, including a very cool use of geographic scaling using multiple ASEs: