We touched on this topic at the beginning of this chapter, so you should have an idea of what we are going to cover now. As you remember, when App Service is created, you have to select (or create) an App Service Plan, which defines both available performance and additional features. Let's cover all three categories, this time focusing on the differences between each tier.

App Service Plans designed for development and testing environments can be found in the Dev / Test category:

We have three different tiers available:

• F1 (Free): The most basic option, with shared infrastructure, 1 GB of memory available, and 60 minutes of compute per day. When using shared tiers, some features of App Services are unavailable (such as Always on, or your selected platform). F1 is perfect for quick-testing or deploying an application for a presentation or demonstration. You will not be charged for using this App Service Plan.
• D1 (Shared): Similar to F1, but this also allows for setting a custom domain for your App Service. What is more, you can run your application four times longer than when using the free tier. Still, this is shared infrastructure, so some features cannot be used.
• B1: The first tier recommended for running production workloads. It guarantees dedicated A-series machines, and more memory and storage. It is also the first tier that you can scale—although only manually. The Basic tier comes with additional versions (B2 and B3), which provide more compute power.

In this category, there are many more options when it comes to choosing different features available. Remember that, in terms of hardware, the Basic tier offers the very same performance as the Standard tier:

Here, we can choose between the following:

• Standard (S1): The same A-series as B1. What we are getting here is autoscaling, staging slots, backups, and the possibility to use Traffic Manager (which will be described in coming chapters). This is the best tier for most production applications, as it supports blue-green deployment scenarios and can handle a bigger load (thanks to integration with Traffic Manager). If you need more compute power, you can choose either S2 or S3.
• Premium (P1v2): This is the new recommended option replacing P1, with new Dv2-series virtual machines underneath. It offers better performance and higher limits when it comes to scaling (a maximum of 20 instances, compared to 10 in Standard) and staging slots. You also have the option to choose P2 or P3.

In general, Standard should meet most requirements when it comes to performance, reliability, and automation possibilities. However, if you are going to run a very popular website in Azure, you may need Premium, as it offers more flexibility and better scalability.

Sometimes you need even more than the Premium tier has to offer. Maybe you have to isolate your application from an external network. Maybe you would like to offer access only to some specific users. Maybe 20 instances are still not enough. This is why Azure introduced the Isolated category:

In this category, we have only one tier divided into three versions:

• Isolated (I1/I2/I3): The same virtual machines as in the Premium tier (Dv2). Also includes huge storage to store your files (1 TB), private app access, an integrated virtual network (so you can access, for example, internal applications), and a more stable environment. This is the most expensive tier, but offers the most when it comes to functionality and the range of features provided.