# TelemetryMetricsTelegraf
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[InfluxDB](https://www.influxdata.com/) reporter for [Telemetry.Metrics](https://github.com/beam-telemetry/telemetry_metrics).
The core idea of this implementation is to avoid any in-memory aggregation and let [telegraf](https://www.influxdata.com/time-series-platform/telegraf) do the heavy lifting.

## Installation

The package can be installed by adding `telemetry_metrics_telegraf` to your list of dependencies in `mix.exs`:

```elixir
def deps do
  [
    {:telemetry_metrics_telegraf, "~> 0.1"}
  ]
end
```

See documentation at [hexdocs.pm](https://hexdocs.pm/telemetry_metrics_telegraf).

## Quickstart guide

Consider we have a freshly generated phoenix app with [telemetry module](https://github.com/phoenixframework/phoenix/blob/master/installer/templates/phx_web/telemetry.ex) and we want to use [instream](https://github.com/mneudert/instream) as influxdb/telegraf client.


Add telemetry_metrics_telegraf to the app telemetry supervision tree
```elixir
defmodule MyAppWeb.Telemetry do
  def init(_arg) do
    children = [
      {:telemetry_poller, measurements: periodic_measurements(), period: 10_000},
      [
        {TelemetryMetricsTelegraf,
         metrics: metrics(),
         adapter:
           {TelemetryMetricsTelegraf.Adapters.Instream, [connection: MyApp.InstreamConnection]}}
      ]
    ]

    Supervisor.init(children, strategy: :one_for_one)
  end

  def metrics do
    [
      # Phoenix Metrics
      summary("phoenix.endpoint.stop.duration"),

      # Database Metrics
      summary("my_app.repo.query.total_time", unit: {:native, :millisecond}, tags: [:source]),
      summary("my_app.repo.query.decode_time", unit: {:native, :millisecond}, tags: [:source]),
      summary("my_app.repo.query.query_time", unit: {:native, :millisecond}, tags: [:source]),
      summary("my_app.repo.query.queue_time", unit: {:native, :millisecond}, tags: [:source]),
      summary("my_app.repo.query.idle_time", unit: {:native, :millisecond}, tags: [:source]),

      # VM Metrics
      summary("vm.memory.total", unit: {:byte, :kilobyte}),
      summary("vm.total_run_queue_lengths.total"),
      summary("vm.total_run_queue_lengths.cpu"),
      summary("vm.total_run_queue_lengths.io")
    ]
  end

  defp periodic_measurements do
    []
  end
end
```

The configuration above emits following influxdb measurements on corresponding telemetry events

```
phoenix.endpoint.stop duration=42
my_app.repo.query,source="users" total_time=10,decode_time=1,query_time=2,
queue_time=3,idle_time=4
vm.memory total=100
vm.total_run_queue_lengths total=42,cpu=40,io=2
```

In order to aggregate emitted measurements we can add the following to our telegraf config

```toml
[[aggregators.basicstats]]
period = "30s"
drop_original = true
namepass = ["vm.*", "my_app.repo.query", "phoenix.endpoint.stop"]
```

## TODO
* [ ] provide an ability to generate telegraf aggregations config from telemetry metrics