Resolving Application Error screen

When trying to access your Shiny application, do you see the screen below?

An application crash

If so, something is wrong with your application. The most common culprits are listed below in order of their likeliness:

• You ran out of system memory. See Limiting the number of R Threads

• You're installing a package from GitHub rather than CRAN. See Using Packrat.

• You're using packages.install() outside of init.R, in your R server function. See Using Packrat

• A required R library has a system-level dependency that isn't articulated in your Aptfile. See Adding System Packages

• You're trying to install rJava without installing a JDK. See Adding System Packages

How can you determine which of the above (or, if you're lucky - an entirely different problem) is responsible for your application crash? Read on!