Graham McIntire
6c5d066121
Without the deferral the cron-driven ETS flush GenServer fires every 7.5s alongside Prometheus scrapes, calls PromEx.get_metrics in a Task, and dies with `Task.await ... time out` (hardcoded 10s) under contention. Mirrors upstream PromEx.Plug, which calls defer_ets_flush after a successful render specifically to suppress the cron while scraping is healthy.
62 lines
1.6 KiB
Elixir
62 lines
1.6 KiB
Elixir
defmodule MicrowavepropWeb.MetricsPlug do
|
|
@moduledoc """
|
|
Serves PromEx metrics at `/metrics`. Optionally gated by a bearer
|
|
token via `config :microwaveprop, :prometheus_auth_token`, sourced
|
|
from the `PROMETHEUS_AUTH_TOKEN` env var in `runtime.exs`.
|
|
"""
|
|
|
|
@behaviour Plug
|
|
|
|
import Plug.Conn
|
|
|
|
@impl true
|
|
def init(opts), do: opts
|
|
|
|
@impl true
|
|
def call(conn, _opts) do
|
|
case authorized?(conn) do
|
|
:ok ->
|
|
body = PromEx.get_metrics(Microwaveprop.PromEx)
|
|
|
|
# Defer the ETS cron flusher; otherwise it runs every
|
|
# `ets_flush_interval` (7.5s) concurrently with scrapes and its
|
|
# `Task.await` (hardcoded 10s) trips under contention, killing
|
|
# the GenServer. Upstream `PromEx.Plug` does the same.
|
|
PromEx.ETSCronFlusher.defer_ets_flush(Microwaveprop.PromEx.__ets_cron_flusher_name__())
|
|
|
|
conn
|
|
|> put_resp_content_type("text/plain; version=0.0.4")
|
|
|> send_resp(200, body)
|
|
|> halt()
|
|
|
|
:denied ->
|
|
conn
|
|
|> put_resp_header("www-authenticate", ~s(Bearer realm="metrics"))
|
|
|> send_resp(401, "unauthorized")
|
|
|> halt()
|
|
end
|
|
end
|
|
|
|
defp authorized?(conn) do
|
|
case Application.get_env(:microwaveprop, :prometheus_auth_token) do
|
|
token when is_binary(token) and token != "" ->
|
|
check_token(conn, token)
|
|
|
|
_ ->
|
|
:ok
|
|
end
|
|
end
|
|
|
|
defp check_token(conn, expected) do
|
|
conn
|
|
|> get_req_header("authorization")
|
|
|> List.first()
|
|
|> case do
|
|
"Bearer " <> token ->
|
|
if Plug.Crypto.secure_compare(token, expected), do: :ok, else: :denied
|
|
|
|
_ ->
|
|
:denied
|
|
end
|
|
end
|
|
end
|