Azure : What do I put in front of my (web) application?

Introduction

In almost every design session, the following question pops up…

“What do I put in front of my web application to secure it?”

Today we will take a look at the different options at hand. Or better said … What is the difference between the following services?

Azure CDN vs Azure Front Door versus Azure Application Gateway (WAF) vs Azure Traffic Manager

 

TL;DR

If you do not want to go through the entire post, here is a brief summary of the different options ;

My gut feeling tells me this will already help out like a lot! 😉

 

Web Application Firewall (WAF) : Azure Front Door vs Azure Application Gateway

Both Azure Front Door and Azure Application Gateway state that they can be configured to act as a Web Application Firewall. They key difference here is that the Azure Application Gateway can do a “detection only”-mode and that it supports CRS 2.2.9, 3.0, and 3.1. This means that there are out-of-the-box rules that provide a baseline security against most of the top-10 vulnerabilities that Open Web Application Security Project (OWASP) identifies. With Azure Front Door, you need to configure the rules yourself to your liking.

In terms of networking, there also is a very important difference between both. An Azure Application Gateway can be deployed (injected) in(to) an Azure VNET (Virtual Network). By doing so, the traffic between this gateway and your internal backend will flow through a private network. With Azure Front Door, your backend is always based on a public endpoint. Though you can harden / lock down the connectivity between Azure Front Door and your application by restricting the ingress of the traffic.

 

Geographic Redundancy : Azure Front Door vs Azure Traffic Manager

If you want to publish your webapp across regions, then you can leverage Azure Front Door or Azure Traffic Manager to do so. The most important thing to know is that Azure Traffic Manager is DNS based and serves as a redirection mechanism. Azure Front Door will serve as an entrypoint (think reverse proxy). So when using Traffic Manager, you will typically look at another reverse proxy / WAF (like Azure Application Gateway) to cover the need for the secure entrypoint for your application. Next to that, the Azure Traffic Manager is more feature rich in terms of the routing mechanisms, though Azure Front Door (just like Azure Application Gateway) have the advantage of working at layer 7 (Reference : OSI Model), thus also do header/path based routing.

 

Caching Content : Azure CDN vs Azure FrontDoor

The first thing to realize is what the intent was of both solutions?

  • Azure CDN is a Content Delivery Network and was designed to delivery content. Think in terms of media files (“video”) for instance.
  • Azure Front Door was built as a scalable entry point for applications (like Office 365)

Both will do caching (check the links above), though they differ in the sweet spots. Azure Front Door will cache files up to 8MB (as a side trait), where you should think that this is mainly done to optimize the delivery of your “web app”. Azure CDN its core function is caching… It was built to ensure that your files would be distributed world wide and delivered from a local pop.

The funky thing here, is that (if you ignore the Verizon and Akamai flavors of Azure CDN) both Azure CDN and Azure Front Door share the same POPs! Though the caching mechanics of both work differently.

 

DDOS

All services will have DDOS protection (“Basic”), as this is native to any Azure service! It is a key component of the Microsoft backbone actually. Though you can augment the services that reside in your VNET with the “Standard” protection. That being said, do know that the Azure Application Gateway does not scale as dynamic as the other services mentioned here (Azure Front Door and Azure Traffic Manager). So this could become a bottleneck for your design.

 

Closing Thoughts

With more than 100 services in Azure, you are bound to have services that overlap in terms of capabilities. I do hope this post provides you with some guidance towards a the external facing endpoints of your application! The above things are the recurring patterns I see in discussions with the organizations I talk to when deploying web applications on Azure.

3 thoughts on “Azure : What do I put in front of my (web) application?

  1. I have Azure Front Door with a Azure Firewall behind this which forwards to an Azure loadbalancer. I have a number of external URLs which need to forward to sites behind the loadbalncer. What rules would i need to configure on the Firewall?

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