Elixir Prometheus Telemetry

This is a simple, bare-bones example Elixir app, which shows how to add basic instrumentation through Telemetry and deliver it to Prometheus

Installation

$ mix deps.get
$ mix deps.compile

Run It

Once you've got all the dependencies pulled, start it up within iex so you can add a few counts to some fictitious commands

$ iex -S mix run

Now that you're within iex, you can add some command counts. Try the following

iex(1)> Basic.Metrics.CommandInstrumenter.execute("ONE")
:ok
iex(2)> Basic.Metrics.CommandInstrumenter.execute("TWO")
:ok
iex(3)> Basic.Metrics.CommandInstrumenter.execute("TWO")
:ok

At this point, you'll have command ONE with a count of 1 and command TWO with a count of 2. To see what metrics Prometheus will scrape from the app, you can visit the following endpoint within your browser

http://localhost:4000/metrics

When you hit this endpoint, you'll see something similar to this

# TYPE basic_command_total counter
# HELP basic_command_total Command Count
basic_command_total{command="ONE"} 1
basic_command_total{command="TWO"} 2
...

Where?

Obviously this is a very small project, and it's meant to be the smallest possible working example I could think to do. So, if you're just trying to get to the one place where all the action is, you'll want to look at lib/basic/metrics/command_instrumenter.ex. Everything interesting is happening there.

Prometheus

To see how metrics are actually pulled into Prometheus, you'll first need to install it and configure it. For more information on installation and configuration, check out the Prometheus Documentation. To add the app's endpoint to Prometheus, you'll want to add the following configuration to the prometheus.yml file under the scrape_configs: element within that file. Again, you'll want to check the documentation to figure out where this file is located for your installation.

scrape_configs:
  - job_name: "basic"
    scheme: "http"
    static_configs:
    - targets: ["localhost:4000"]

Once you start the Prometheus service, you should be able to explore the UI by visiting http://localhost:9090/graph within your browser. From the dropdown, select the the basic_command_total element, and add it to a graph by clicking the Execute button. Click on the Graph tab, and you'll see your app metrics! Enjoy!