PromEx

Prometheus metrics and Grafana dashboards for all of your favorite Elixir libraries.

Contents

• Installation
• Design Philosophy
• Available Plugins
• Grafana Dashboards
• Setting Up Metrics
• Performance Concerns
• Attribution

Installation

This library is still under active development with changing API contracts and forked dependencies...use at your own risk for now :).

Available in Hex, the package can be installed by adding prom_ex to your list of dependencies in mix.exs:

def deps do
  [
    {:prom_ex, "~> 0.1.13-beta"}
  ]
end

Documentation can be found at https://hexdocs.pm/prom_ex.

Design Philosophy

With the widespread adoption of the Telemetry library and the other libraries in the BEAM Telemetry GitHub Org, we have reached a point where we have a consistent means of surfacing application and library metrics. This allows us to have a great level of insight into our applications and dependencies given that they all leverage the same fundamental tooling. The goal of this project is to provide a "Plug-in" style library where you can easily add new plug-ins to surface metrics so that Prometheus can scrape them. Ideally, this project acts as the "Metrics" pillar in your application (in reference to The Three Pillars of Observability).

To this end, while PromEx does provide a certain level of configurability (like the polling rate, starting behaviour for manual metrics and all the options that the plugins receive), the goal is not to make an infinitely configurable tool. For example, you are not able to edit the names/descriptions of Prometheus metrics via plugin options or even the tags that are attached to the data points.

Instead, if there things that you don't agree with or that are incompatible with your usage of a certain 1st party plugin and want to edit how the PromEx plugins react to Telemetry events, it is recommended that you fork the plugin in question and edit it to your specific use case. If you think that the community can benefit for your changes, do not hesitate to make a PR and I'll be sure to review it. This is not to say that event configurability will never come to PromEx, but I want to make sure that the public facing API is clean and straightforward and not bogged down with configuration. That and the Grafana dashboards would then have to become templatized to accommodate all this configurability.

PromEx provides a few utilities to you in order to accomplish this goal:

• The PromEx.Plug module that can be used in your Phoenix or Plug application to expose the collected metrics
• A Mix task to upload the provided complimentary Grafana dashboards
• A Mix task to create a PromEx metrics capture module
• A behaviour that defines the contract for PromEx plug-ins
• A behaviour that defines the functionality of a PromEx metrics capture module
• Grafana dashboards tailored to each specific Plugin so that metrics work out of the box with dashboards

Available Plugins

Plugin	Status	Description
PromEx.Plugins.Application	Beta	Collect metrics on your application dependencies
PromEx.Plugins.Beam	Beta	Collect metrics regarding the BEAM virtual machine
PromEx.Plugins.Phoenix	Beta	Collect request metrics emitted by Phoenix
PromEx.Plugins.Ecto	Beta	Collect query metrics emitted by Ecto
PromEx.Plugins.Oban	Beta	Collect queue processing metrics emitted by Oban
PromEx.Plugins.PhoenixLiveView	In progress	Collect metrics emitted by Phoenix LiveView
PromEx.Plugins.Broadway	Coming soon	Collect message processing metrics emitted by Broadway
PromEx.Plugins.Absinthe	Coming soon	Collect GraphQL metrics emitted by Absinthe
PromEx.Plugins.Finch	Coming soon	Collect HTTP request metrics emitted by Finch
PromEx.Plugins.Redix	Coming soon	Collect Redis request metrics emitted by Redix
More to come...

Grafana Dashboards

PromEx comes with a custom tailored Grafana Dashboard per Plugin. Click here to check out sample screenshots of each Plugin specific Grafana Dashbaord.

Setting Up Metrics

The goal of PromEx is to have metrics set up be as simple and streamlined as possible. In that spirit, all that you need to do to start leveraging PromEx along with the built-in plugins is to run the following mix task:

$ mix prom_ex.gen.config --datasource YOUR_PROMETHEUS_DATASOURCE_ID

Then add the generated module to your application.ex file supervision tree:

defmodule MyCoolApp.Application do
  use Application

  def start(_type, _args) do
    children = [
      ...

      MyCoolApp.PromEx
    ]

    opts = [strategy: :one_for_one, name: MyCoolApp.Supervisor]
    Supervisor.start_link(children, opts)
  end
end

With that in place, all that you need to do is then add the PromEx plug somewhere in your endpoint.ex file (I would suggest putting it before your plug Plug.Telemetry call so that you do not pollute your logs with calls to /metrics):

defmodule MyCoolAppWeb.Endpoint do
  use Phoenix.Endpoint, otp_app: :my_cool_app

  ...

  plug PromEx.Plug, prom_ex_module: MyCoolApp.PromEx
  # Or plug PromEx.plug, path: "/some/other/metrics/path", prom_ex_module: MyCoolApp.PromEx

  ...

  plug Plug.RequestId
  plug Plug.Telemetry, event_prefix: [:phoenix, :endpoint]

  ...

  plug MyCoolAppWeb.Router
end

With that in place, all you need to do is start your server and you should be able to hit your metrics endpoint and see your application metrics:

$ curl localhost:4000/metrics
# HELP my_cool_app_application_dependency_info Information regarding the application's dependencies.
# TYPE my_cool_app_application_dependency_info gauge
my_cool_app_application_dependency_info{modules="69",name="hex",version="0.20.5"} 1
my_cool_app_application_dependency_info{modules="1",name="connection",version="1.0.4"} 1
my_cool_app_application_dependency_info{modules="4",name="telemetry_poller",version="0.5.1"} 1
...
...

Be sure to check out the module docs for each plugin that you choose to use to ensure that you are familiar with all of the options that they provide.

Performance Concerns

You may think to yourself that with all these metrics being collected and scraped, that the performance of your application my be negatively impacted. Luckily PromEx is built upon the solid foundation established by the Telemetry, TelemetryMetrics, and the TelemetryMetricsPrometheus projects. These libraries were designed to be as lightweight and performant as possible. From some basic stress tests that I have run, I have been unable to observe any meaningful or measurable performance reduction (thank you OTP and particularly ETS ;)). Here are six sample stress tests using wrk2 with PromEx enabled and disabled with the following configuration:

defmodule WebApp.PromEx
  use PromEx, otp_app: :web_app

  @impl true
  def plugins do
    [
      {PromEx.Plugins.Application, otp_app: :web_app},
      PromEx.Plugins.Beam,
      {PromEx.Plugins.Phoenix, router: WebAppWeb.Router}
    ]
  end
end

With out PromEx metrics collection:

$ wrk2 -t5 -c50 -R 1000 -d10s 'http://localhost:4000/'
Running 10s test @ http://localhost:4000/
  5 threads and 50 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     4.25ms    1.02ms  22.00ms   71.90%
    Req/Sec       -nan      -nan   0.00      0.00%
  10003 requests in 10.01s, 38.60MB read
Requests/sec:    999.78
Transfer/sec:      3.86MB

$ wrk2 -t5 -c50 -R 1000 -d10s 'http://localhost:4000/'
Running 10s test @ http://localhost:4000/
  5 threads and 50 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     4.15ms    0.92ms  15.06ms   67.75%
    Req/Sec       -nan      -nan   0.00      0.00%
  10002 requests in 10.00s, 38.59MB read
Requests/sec:    999.73
Transfer/sec:      3.86MB

$ wrk2 -t5 -c50 -R 1000 -d10s 'http://localhost:4000/'
Running 10s test @ http://localhost:4000/
  5 threads and 50 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     4.23ms    1.31ms  29.82ms   84.14%
    Req/Sec       -nan      -nan   0.00      0.00%
  10001 requests in 10.00s, 38.59MB read
Requests/sec:    999.82
Transfer/sec:      3.86MB

With PromEx metrics collection:

$ wrk2 -t5 -c50 -R 1000 -d10s 'http://localhost:4000/'
Running 10s test @ http://localhost:4000/
  5 threads and 50 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     4.55ms    1.69ms  36.86ms   94.40%
    Req/Sec       -nan      -nan   0.00      0.00%
  9999 requests in 10.00s, 38.58MB read
Requests/sec:   1000.11
Transfer/sec:      3.86MB

$ wrk2 -t5 -c50 -R 1000 -d10s 'http://localhost:4000/'
Running 10s test @ http://localhost:4000/
  5 threads and 50 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     4.42ms    1.56ms  31.58ms   90.48%
    Req/Sec       -nan      -nan   0.00      0.00%
  10004 requests in 10.00s, 38.60MB read
Requests/sec:    999.93
Transfer/sec:      3.86MB

$ wrk2 -t5 -c50 -R 1000 -d10s 'http://localhost:4000/'
Running 10s test @ http://localhost:4000/
  5 threads and 50 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     4.39ms    1.09ms  18.56ms   72.96%
    Req/Sec       -nan      -nan   0.00      0.00%
  10001 requests in 10.00s, 38.59MB read
Requests/sec:    999.81
Transfer/sec:      3.86MB

Attribution

It wouldn't be right to not include somewhere in this project a "thanks" to the various projects that helped make this possible:

• The various projects available in BEAM Telemetry
• All of the Prometheus libraries that Ilya Khaprov (@deadtrickster) maintains
• The logo for the project is an edited version of an SVG image from the unDraw project