Modularizing an Existing Shiny App

Peter Baranovskiy breaks it down:

There are multiple tutorials available online on writing modular Shiny apps. So why one more? Well, when I just started with building modular apps myself, these didn’t do much for me. So I really only learned how to write modules when I had an opportunity to team up with an experienced R Shiny developer. The reason I guess is that Shiny modules is an advanced topic, and you typically get to writing modules only when you finally need to scale your apps – and keep opportunities for further scaling open. This typically means when your app goes into production. By then you probably have already developed multiple apps, and switching over to a way of thinking required to write modules may be challenging. If you don’t know what modules are, I recommend starting here and then coming back to this post. Otherwise, read on.

So, I decided to try a different approach and instead of building a simple modular app from scratch, to go in the opposite direction by breaking down a complex real-life app into modules. Here’s the app’s original non-modular code. Note a single app.R file that contains the entire app. static_assets.R includes some object definitions which I moved to a separate file for convenience. calgary_crime_data_prep.R is not part of the app; it is a data retrieval and cleaning script executed once a month with cron. Running the script each time the app launches would have made it extremely slow and would use way too much bandwidth, as the script downloads and processes 150+ Mb of data on each run.

Read on for the reasoning behind using modules, as well as Peter’s notes on the process.