Enable Always On when running on dedicated App Service Plan

Azure Functions can run on either a Consumption Plan or a dedicated App Service Plan. If you run in a dedicated mode, you need to turn on the Always On setting for your Function App to run properly. The Function runtime will go idle after a few minutes of inactivity, so only HTTP triggers will actually "wake up" your functions. This is similar to how WebJobs must have Always On enabled.

To turn on Always On, go to Function App Settings -> App Service Settings -> Application settings -> Always On. (Tip: you can also search for "Always on" in the search box at the top.)

Note that the Always On setting is only available when running on a Basic or higher tier of App Service Plan. While it is possible to use a Free or Shared tier App Service Plan, most customers will be better suited with a Consumption App Service Plan which offers a substantial number of free executions (see Azure Functions Consumption Plan Pricing. Free or Shared can still be used for development purposes, but triggers will only execute when the Function App is active in the Azure Portal and the first request to an HTTP trigger may be very slow.