add HTTP telemetry events for Cog startup

config/config.exs

@@ -1,6 +1,18 @@
 use Mix.Config
 import Cog.Config.Helpers
 
+# ========================================================================
+# Cog Telemetry - By default, Cog is configured to send an event to the
+# Operable telemetry service every time it starts. This event contains a
+# unique ID (based on the SHA256 of the UUID for your operable bundle)
+# and the Cog version number.
+#
+# If you would like to opt-out of sending this data, you can set the
+# COG_TELEMETRY environment variable to "false".
+# ========================================================================
+
+config :cog, :telemetry, ensure_boolean(System.get_env("COG_TELEMETRY") || true)
+
 # ========================================================================
 # Set this to :unenforcing to globally disable all access rules.
 # NOTE: This is a global setting.

lib/cog.ex

@@ -50,6 +50,9 @@ defmodule Cog do
         Logger.info("Ensuring common templates are up-to-date")
         Cog.Repository.Templates.refresh_common_templates!
 
+        # Send a start event to the Operable telemetry service
+        Cog.Telemetry.send_event(:start)
+
         {:ok, top_sup}
       error ->
         error

lib/cog/telemetry.ex

@@ -0,0 +1,48 @@
+defmodule Cog.Telemetry do
+  require Logger
+
+  @telemetry_url "asdf;a8sw3rjasdfkl;asdf"
+
+  def send_event(type) do
+    if telemetry_enabled do
+      spawn fn ->
+        case build_event(type) do
+          {:ok, event_body} ->
+            post_telemetry(type, event_body)
+        end
+      end
+    end
+  end
+
+  defp build_event(:start) do
+    bundle_id =
+      "operable"
+      |> Cog.Queries.Bundles.bundle_id_from_name
+      |> Cog.Repo.one
+
+    case bundle_id do
+      nil ->
+        {:error, "Cannot find ID for embedded bundle."}
+      bundle_id ->
+        telemetry_id = Base.encode16(:crypto.hash(:sha256, bundle_id))
+        {:ok, version} = :application.get_key(:cog, :vsn)
+        {:ok, %{ cog: %{ id: telemetry_id, version: to_string(version) }}}
+    end
+  end
+
+  defp telemetry_enabled do
+    Application.fetch_env!(:cog, :telemetry)
+  end
+
+  defp post_telemetry(event_type, event_body) do
+    post_url = @telemetry_url <> "/events/" <> Atom.to_string(event_type)
+    post_body = Poison.encode!(event_body)
+
+    Logger.info "Sending telemetry data to Operable: #{post_body}"
+    Logger.info "To disable telemetry, set the COG_TELEMETRY environment variable to false."
+
+    HTTPotion.post(post_url, headers: ["Content-Type": "application/json",
+                                       "Accepts": "application/json"],
+                             body: post_body)
+  end
+end