 If I had to pick one feature of App Service, I think it would have to be deployment slots as my favorite feature. Deployment slots allow our customers, or any user of App Service, to have what I call zero downtime deployment. Historically, when you deploy your application to a web server, at some point you have to put up a web page saying, we'll be right back, don't worry, site's not gone, but we're updating it. And when you update it, you copy the files to the server. Problem is, you don't know if those files have actually landed correctly or not until you take that page down and open it up to the world. At which point, if something bad happened, the entire world is there to see it, and you have to put the page back and try to troubleshoot without being able to see it. Deployment slots, however, give you an invisible version of your site behind your production slot. You can deploy there to your heart's content while your customers continue to use the production site. However, you can access that hidden or staging slot of your website. So you can go and make sure everything landed correctly, you can do any smoke test that you might want to do, and when you're ready to share it with the world, you simply swap the slots and everyone sees the new value with zero downtime. Let's say something still goes wrong, traffic starts to come on really heavily, you have a performance issue, all you have to do is swap them back, and then what used to be production is now back there again and you're ready to rock and roll. So deployment slots, zero downtime deployment, it's an amazing feature of App Service.