Chapter 1, Preparing for the Journey Ahead, starts our odyssey by introducing Elixir. It starts by covering the data types of Elixir and how pattern matching works, moving on to then explore how to create modules and functions, while also seeing, among other things, how to work with collections and use control flow in Elixir. After reading this chapter, you will be familiar with Elixir's syntax, and how to use it to write some simple functions.
Chapter 2, Innards of an Elixir Project, kicks off by analyzing what makes an Elixir application and what an Elixir project is. It then examines how to use the Mix tool to create projects and manage their dependencies. It's here that we'll create an umbrella project for the ElixirDrip application that will be developed throughout this book.
Chapter 3, Processes – The Bedrock for Concurrency and Fault-tolerance, starts by exploring how the BEAM VM works and its concurrency model, the actor model. Then, it shows how to create and work with processes in Elixir, building a piece of the ElixirDrip application as an example. This chapter also explores how to link and monitor processes, and how Supervisors build on top of this to detect crashing processes. Finally, this chapter explores how we can group Supervisors to create supervision trees, which enable the creation of fault-tolerant applications.
Chapter 4, Powered by Erlang/OTP, introduces OTP and examines both the battle-tested OTP abstractions that Elixir inherited from Erlang, such as GenServer and Erlang Term Storage, and the new Agent, Task and Registry abstractions that Elixir brought to life. Each abstraction is put to good use by implementing a media cache, a text search function, and a search results cache.
Chapter 5, Demand-Driven Processing, goes a long way to explain how the GenStage and Flow abstractions introduced by Elixir let the developer process data using a demand-driven paradigm. Instead of processing data as fast as possible to match the rate at which data is produced, this approach turns the problem on its head and forces the producer to inject new data into the pipeline at a rate controlled by the data consumers. It's in this chapter that the upload and download pipelines of the ElixirDrip application are developed.
Chapter 6, Metaprogramming–Code that Writes Itself, unveils the constructs that allow the developer to easily control what happens in compile time, by writing regular Elixir code that produces more code. The chapter starts by iterating on a macro whose purpose is to measure the time a function takes to execute, and ends by implementing a Domain-Specific language which significantly simplifies the media upload and download pipelines defined in the previous chapter.
Chapter 7, Persisting Data Using Ecto, explores how to work with databases. It starts by explaining how to connect an application to a database and how database structure changes can be applied as migrations. It then examines how to create and enforce table relations and how to use changesets to persist and update data. In the end, different ways to query the database are analyzed.
Chapter 8, Phoenix: A Flying Web Framework, introduces the Phoenix framework and explains how to use it to add a web layer to our ElixirDrip application. The chapter begins by the conventional topics, such as routers, controllers, and views, but toward the end, also explores more progressive concepts, such as building a JSON API or using Phoenix Channels.
Chapter 9, Find Zen through Testing, dives into different kinds of testing. It begins with unit and integration testing, and goes on to explore more elaborate topics, such as how to test macros and Phoenix components, and also how to write property tests.
Chapter 10, Deploy on the Cloud, takes the ElixirDrip application running to its live environment, storing media from real users. This chapter starts by explaining how to use Distillery to package the application in an efficient way and then introduces the concept of application containerization and how it suits the development and deployment phases of our application. The last half of the chapter examines how to deploy the application to a Kubernetes cluster and,ultimately, how to automate this process by using a continuous integration service.
Chapter 11, Keeping an Eye on Your Processes, teaches you how to monitor your application so that you can ensure that your application is working as it should. You will begin by learning how to collect metrics from your application. Then, we will teach you how to use an Erlang tool, called Observer, which allows us to tap into what is going on inside the BEAM virtual machine. You will learn how to get statistics from the BEAM (such as CPU and memory utilization), as well as from the state of each process inside your application. Lastly, we’ll look at how to inspect our application and check what’s happening under the hood. You will learn how to investigate a bottleneck by profiling our ElixirDrip application, while also checking how to use Erlang’s standard library to trace calls to a certain process.
