Shiny Server unable to open connection to any shiny application

Question

When I attempt to connect to any shiny application on my webserver I receive the following error:

   ERROR: cannot open the connection

I am currently storing the application within the /srv/shiny-server folder on the server and the folder does currently have the correct read/write permissions. Earlier when I uploaded my application it ran without issue but I made several changes and when I updated the files I suddenly started getting this error. I tried rolling back all of the changes but the error persisted and so eventually I attempted uploading an example application from the Shiny Website and that also gets the same error.

Here is the code for the sample application I'm currently trying to get working but I do not think that it is the issue:

ui.R

    library(shiny)

bootstrapPage(

  selectInput(inputId = "n_breaks",
              label = "Number of bins in histogram (approximate):",
              choices = c(10, 20, 35, 50),
              selected = 20),

  checkboxInput(inputId = "individual_obs",
                label = strong("Show individual observations"),
                value = FALSE),

  checkboxInput(inputId = "density",
                label = strong("Show density estimate"),
                value = FALSE),

  plotOutput(outputId = "main_plot", height = "300px"),

  # Display this only if the density is shown
  conditionalPanel(condition = "input.density == true",
                   sliderInput(inputId = "bw_adjust",
                               label = "Bandwidth adjustment:",
                               min = 0.2, max = 2, value = 1, step = 0.2))
  )

server.R

library(shiny)


function(input, output) {

  output$main_plot <- renderPlot({

    hist(faithful$eruptions,
         probability = TRUE,
         breaks = as.numeric(input$n_breaks),
         xlab = "Duration (minutes)",
         main = "Geyser eruption duration")

    if (input$individual_obs) {
      rug(faithful$eruptions)
    }

    if (input$density) {
      dens <- density(faithful$eruptions,
                      adjust = input$bw_adjust)
      lines(dens, col = "blue")
    }

  })
}

Answer 1

I opened up the logs for the application located in /var/log/shiny-server and it turned out that permission was being denied to the folder. After googling the problem I found this question which helped me solve the issue