The difference between the structures of shiny apps for local and server deployment

Question

I've made some shiny apps that work well when run locally, but not when deployed online on a shiny server (placed in /srv/shiny-server/). Here are the contents of a simple shiny_test.R file as an example. When deployed online it just displays an index (see image).

library(shiny)

###################################################
# ui
###################################################
# Define UI for app that draws a histogram ----
ui <- fluidPage(
  
  # App title ----
  titlePanel("Hello Shiny!"),
  
  # Sidebar layout with input and output definitions ----
  sidebarLayout(
    
    # Sidebar panel for inputs ----
    sidebarPanel(
      
      # Input: Slider for the number of bins ----
      sliderInput(inputId = "bins",
                  label = "Number of bins:",
                  min = 1,
                  max = 50,
                  value = 30)
      
    ),
    
    # Main panel for displaying outputs ----
    mainPanel(
      
      # Output: Histogram ----
      plotOutput(outputId = "distPlot")
      
    )
  )
)

###################################################
# server
###################################################
# Define server logic required to draw a histogram ----
server <- function(input, output) {
  
  # Histogram of the Old Faithful Geyser Data ----
  # with requested number of bins
  # This expression that generates a histogram is wrapped in a call
  # to renderPlot to indicate that:
  #
  # 1. It is "reactive" and therefore should be automatically
  #    re-executed when inputs (input$bins) change
  # 2. Its output type is a plot
  output$distPlot <- renderPlot({
    
    x    <- faithful$waiting
    bins <- seq(min(x), max(x), length.out = input$bins + 1)
    
    hist(x, breaks = bins, col = "#75AADB", border = "white",
         xlab = "Waiting time to next eruption (in mins)",
         main = "Histogram of waiting times")
    
  })
  
}

###################################################
# Run app
###################################################
# runApp("my_app")
shinyApp(ui = ui, server = server)

I've seen that historically shiny apps used to have two files - server.R and ui.R, and wondered whether that would solve it, but I'm not sure what the rules are?

Answer 1

Unfortunately this is not the time to be creative with file names. Rename shiny_test.R to app.R and try again. Proof:

Download shiny server docker image so that I don't have to install it on my system.

➜ docker pull rocker/shiny
Using default tag: latest
latest: Pulling from rocker/shiny
d7bfe07ed847: Pull complete 
896c02edbac0: Pull complete 
5297d3569d0f: Pull complete 
267bd2730782: Pull complete 
c9a275481623: Pull complete 
e82cec2b1844: Pull complete 
Digest: sha256:bc29f76ebe1f1e32d798cadff9e383fecfab9e9f16bf76148c7ed75dbf9965ee
Status: Downloaded newer image for rocker/shiny:latest
docker.io/rocker/shiny:latest

Run the broken app with shiny_test.R and the result.

➜ docker run --rm -p 3838:3838 -v /.../test:/srv/shiny-server/test rocker/shiny
[s6-init] making user provided files available at /var/run/s6/etc...exited 0.
[s6-init] ensuring user provided files have correct perms...exited 0.
[fix-attrs.d] applying ownership & permissions fixes...
[fix-attrs.d] done.
[cont-init.d] executing container initialization scripts...
[cont-init.d] 01_set_env: executing... 
skipping /var/run/s6/container_environment/HOME
[cont-init.d] 01_set_env: exited 0.
[cont-init.d] done.
[services.d] starting services
[services.d] done.

And then rename the R script and run again.

➜ mv shiny_test.R app.R
➜ docker run --rm -p 3838:3838 -v /.../test:/srv/shiny-server/test rocker/shiny
[s6-init] making user provided files available at /var/run/s6/etc...exited 0.
[s6-init] ensuring user provided files have correct perms...exited 0.
[fix-attrs.d] applying ownership & permissions fixes...
[fix-attrs.d] done.
[cont-init.d] executing container initialization scripts...
[cont-init.d] 01_set_env: executing... 
skipping /var/run/s6/container_environment/HOME
[cont-init.d] 01_set_env: exited 0.
[cont-init.d] done.
[services.d] starting services
[services.d] done.