Rob Allen has continued his series of posts covering the use of PHP on the OpenWhisk platform. In his latest tutorial he shows how to use dependency injection for use in "non-trivial PHP applications".

Any non-trivial PHP applications use various components to do its work, from PDO though to classes from Packagist. It’s fairly common in a standard PHP application to use Dependency Injection to configure and load these classes when necessary. How do we do this in a serverless environment such as OpenWhisk?

This question comes up because we do not have a single entry point into our application, instead we have one entry point per action. If we’re using Serverless to write an API, then we probably

He uses a common connection type - PDO to a database - to illustrate a method for injecting dependencies in a serverless application. In his example, he starts with a simple script that returns a set of "todo" items from the database (with the PDO connection code embedded in it). Using dependency injection is a better way to manage that PDO connection so he shows how to update it to use the Pimple DI container and inject it via the constructor to make it available to the rest of the application.