OpenTelemetry traces on server starting up

[marcosnav]

While testing the out-of-the-box features Shiny provides for OTel traces and logs in a few observability tools, I noticed that the very first span Shiny creates is session_start, and with a few more custom instrumentation I noticed there is a gap of time with unknown events between the call to shinyApp(ui, server) and the first session_start event.

There might be valuable information on the events happening while shiny starts up the server.

For example, similar code to the following snippet shows a span of ~12secs that happens just before session_start shows up.

.shiny_startup_span <- otel::start_span("shiny_framework_startup", attributes = list(app.instrumentation = "custom"))

server <- function(input, output) {
  otel::end_span(.shiny_startup_span)
  # ...
}

shinyApp(ui=ui, server=server)

So there is a ~12s span of things happening in Shiny just after shinyApp is called and the server function is called.

[cpsievert]

Hi @marcosnav, is this something you're noticing with a minimal Hello World Shiny app? Or is this something specific to a more complex app? If you are doing something like reading in lots of data at the top level of your server function, then that could explain the startup time here.

[marcosnav]

Hi @cpsievert, the shared example is a quite complex app. But the same can be seen in simple apps, like the one I'm sharing below.

library(shiny)
library(otel)
library(otelsdk)

ui <- fluidPage(
  titlePanel("Hello Shiny"),
  sidebarLayout(
    sidebarPanel(
      sliderInput("bins", "Number of bins:", min = 1, max = 50, value = 30)
    ),
    mainPanel(
      plotOutput("distPlot")
    )
  )
)

.shiny_startup_span <- otel::start_span(
  "shiny_framework_startup",
  attributes = list(app.instrumentation = "custom")
)

server <- function(input, output) {
  otel::end_span(.shiny_startup_span)

  output$distPlot <- renderPlot({
    x <- faithful$waiting
    bins <- seq(min(x), max(x), length.out = input$bins + 1)
    hist(x, breaks = bins, col = "steelblue", border = "white",
         main = "Old Faithful waiting times",
         xlab = "Waiting time (min)")
  })
}

shinyApp(ui = ui, server = server)