I've used shinyapps.io in the past and it provides a loading animation (spinner) while the application starts up. This is useful because I load 200MB of .RData-files into the memory (once on startup, not for every server()). This takes up to 40 seconds (in future, I will transition towards storing the data in a database, but for now this is what I got).
For other applications, I've used the docker image rocker/shiny and wanted to fully transition to a Docker-based approach and put all my shiny applications on one server and move away from shinyapps.io. However, the one issue I have with this application is that it does not display a loading animation while it starts so the user is left with a grey screen for a good 30-40 seconds while the data is loaded in the background.
As for the code, I load all data and then I source ui.R and server.R before running shiny::shinyApp(ui = ui, server = server).
Does any of you know a way to specify a loading animation on startup of the application (I haven't found anything in the server configuration itself but I could have overlooked something)? Or have you found a nice workaround to achieve the desired result?
So what I ended up doing was to follow this workaround suggested here: http://www.mazsoft.com/blog/post/2018/01/01/show-progress-bar-when-pre-loading-data-in-shiny-app
The idea is that we initialize all data variables with NULL. Then there is a readData() function outside of server and ui where we load all the data into the global variables and at the beginning of the server function block we check if one of our data variables is.null() which would lead us to call the readData() function.
It is an okay solution for my problem as it's a nice workaround, yet I wasn't able to figure out how to actually display a loading animation on startup, just while loading the data. I hope this helps people with a similar same problem.