Designing for Scalability with Erlang/OTP

Chapter 10. Special Processes and Your Own Behaviors

OTP behaviors, in the vast majority of cases, provide you with the concurrency design patterns you need in your projects. There might, however, be occasions where you want to create an OTP-compliant application while attaching processes that are not standard behaviors to your supervision tree. For instance, existing behaviors might have performance impacts caused by the overhead of the layers added as a result of abstracting out the generic parts and error handling. You may want to write new behaviors after separating your code into generic and specific modules. Or you might want to do something as simple as adding pure Erlang processes to a supervision tree, making your release OTP compliant beyond the capabilities provided by supervision bridges. For instance, you might have to preserve that proof of concept you wrote when you first started exploring Erlang that, against your better judgment, wound up in production.¹

We refer to a process that can be added to an OTP supervision tree and packaged in an application as a special process. This chapter explains how to write your own special processes, providing you with the flexibility of pure Erlang while retaining all of the advantages of OTP. We also explain how you can take your special processes a step further, turning them into OTP behaviors by splitting the code into generic and specific modules that interface with each other through predefined callback functions. If you are ...