Chapter 6. Fault tolerance with Supervisors
This chapter covers
- Using the OTP Supervisor behavior
- Working with Erlang Term Storage (ETS)
- Using Supervisors with normal processes and other OTP behaviors
- Implementing a basic worker-pool application
In the previous chapter, you built a naïve Supervisor made from primitives provided by the Elixir language: monitors, links, and processes. You should now have a good understanding of how Supervisors work under the hood.
After teasing you in the previous chapter, in this chapter I’ll finally show you how to use the real thing: the OTP Supervisor behavior. The sole responsibility of a Supervisor is to observe an attached child process, check to see if it goes down, and take some action if that happens.
The OTP version offers a few more bells and whistles than your previous implementation of a Supervisor. Take restart strategies, for example, which dictate how a Supervisor should restart the children if something goes wrong. Supervisor also offers options for limiting the number of restarts within a specific timeframe; this is especially useful for preventing infinite restarts.
To really understand Supervisors, it’s important to try them for yourself. Therefore, instead of boring you with every single Supervisor option, I’ll walk you through building the worker-pool application shown in its full glory (courtesy of the Observer application) in figure 6.1.
