Add a Health Check to a Shiny App

Registers one or more healthcheck endpoints on a Shiny app by decorating the app object's internal HTTP handler. Requests matching a registered path (via GET) are answered by handler before any UI rendering, session creation, or authentication occurs; all other requests fall through to the app unchanged.

Because the interception happens on the app object's own handler, no uiPattern adjustment is required and the endpoint works regardless of how the app was constructed (plain shiny::shinyApp(), golem, UI wrappers, etc.).

Registrations stack: call add_healthcheck() multiple times with different paths to expose e.g. separate liveness and readiness endpoints (/livez, /readyz) with their own handlers.

Usage

add_healthcheck(
  app,
  path = "/health",
  handler = health_handler_default,
  verbose = shiny::in_devmode()
)

Arguments

app

A shiny application object, typically created using shiny::shinyApp().

path

Character vector of URL paths to register (each must begin with /). Default "/health".

handler

A healthcheck handler: a function of req returning a health_response(), a shiny::httpResponse(), or a named list. See health_handler_default() for the full contract. Errors thrown by the handler are converted into a 503 "fail" response.

verbose

Logical; log a console message for each healthcheck request received. Evaluated once at registration time. Defaults to shiny::in_devmode().

Value

The modified app object, classed c("shinyhealth_app", "shiny.appobj"), with registration metadata stored in the shinyhealth attribute.

See also

health_response(), health_handler_default(), has_healthcheck(), healthcheck_paths()

Examples

app <- shiny::shinyApp(
  ui = shiny::fluidPage("hello"),
  server = function(input, output, session) {}
)

app <- add_healthcheck(app)
has_healthcheck(app)
#> [1] TRUE
healthcheck_paths(app)
#> [1] "/health"

# stack a second endpoint with a custom handler
app <- add_healthcheck(app, path = "/readyz", handler = function(req) {
  health_response(checks = list(database = list(status = "pass")))
})
healthcheck_paths(app)
#> [1] "/health" "/readyz"