kill prometheus errors at startup when prometheus is not configured

config/config.exs

@@ -239,7 +239,8 @@ config :pleroma, :instance,
   welcome_message: nil,
   max_report_comment_size: 1000,
   safe_dm_mentions: false,
-  healthcheck: false
+  healthcheck: false,
+  instrumentation: false
 
 config :pleroma, :app_account_creation, enabled: true, max_requests: 25, interval: 1800
 

docs/config.md

@@ -104,6 +104,7 @@ config :pleroma, Pleroma.Emails.Mailer,
 * `max_report_comment_size`: The maximum size of the report comment (Default: `1000`)
 * `safe_dm_mentions`: If set to true, only mentions at the beginning of a post will be used to address people in direct messages. This is to prevent accidental mentioning of people when talking about them (e.g. "@friend hey i really don't like @enemy"). (Default: `false`)
 * `healthcheck`: if set to true, system data will be shown on ``/api/pleroma/healthcheck``.
+* `instrumentation`: enable instrumenters for Prometheus metrics
 
 ## :app_account_creation
 REST API for creating an account settings

lib/pleroma/application.ex

@@ -25,7 +25,10 @@ defmodule Pleroma.Application do
     import Cachex.Spec
 
     Pleroma.Config.DeprecationWarnings.warn()
-    setup_instrumenters()
+
+    if Pleroma.Config.get([:instance, :instrumentation]) do
+      setup_instrumenters()
+    end
 
     # Define workers and child supervisors to be supervised
     children =