Finch: Failed to lookup telemetry handlers

Questions / Help
1

I have a simple Mix Task in one of my projects for making a request to a service with Finch. Here is a simple example of doing such a thing.

defmodule Mix.Tasks.Example.Request do
  use Mix.Task

  def run([]) do
    Finch.start_link(name: MyFinch)

    Finch.build(:get, "https://github.com")
    |> Finch.request(MyFinch)
  end
end

If I run this with mix example.request, I get the following output:

$ mix example.request
Compiling 1 file (.ex)

09:47:57.913 [warning] Failed to lookup telemetry handlers. Ensure the telemetry application has been started. 

09:47:57.920 [warning] Failed to lookup telemetry handlers. Ensure the telemetry application has been started. 

09:47:57.921 [warning] Failed to lookup telemetry handlers. Ensure the telemetry application has been started. 

09:47:57.921 [warning] Failed to lookup telemetry handlers. Ensure the telemetry application has been started. 

09:47:58.160 [warning] Failed to lookup telemetry handlers. Ensure the telemetry application has been started. 

09:47:58.161 [warning] Failed to lookup telemetry handlers. Ensure the telemetry application has been started. 

09:47:58.162 [warning] Failed to lookup telemetry handlers. Ensure the telemetry application has been started. 

09:47:58.162 [warning] Failed to lookup telemetry handlers. Ensure the telemetry application has been started. 

09:47:58.388 [warning] Failed to lookup telemetry handlers. Ensure the telemetry application has been started. 

09:47:58.388 [warning] Failed to lookup telemetry handlers. Ensure the telemetry application has been started.

The request completes as expected, but I get all of these warnings related to my telemetry application not being started. I don’t want to start any telemetry application, though. It’s a simple one-off Mix task that has nothing to do with the rest of my app per se and I don’t want to run app.start or similar.

Interestingly, if I do the same thing with a simple exs script, I get no warnings.

Mix.install([:finch])

Finch.start_link(name: MyFinch)

Finch.build(:get, "https://github.com")
|> Finch.request(MyFinch)

I have three questions:

  1. Why do I get these warnings?
  2. How can I silence them?
  3. Why do they only show up when run in a Mix task within the application, but not in a standalone Mix install script? I’m guessing something specified in my mix.exs file or in my config.exs file(s) is causing this, but not sure which.

Cheers,

2

Found it. The discrepancy lies in the fact that Mix.install/1 starts the application for each dependency by default.

Solution is to just add Application.ensure_started(:telemetry) at the beginning of the Mix task.

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