Instrument your Elixir application with OpenTelemetry

This walkthrough shows how to add observability to your Elixir application using the OpenTelemetry Elixir libraries and tools.

Feature	Supported
Automatic Instrumentation	No
Automatic OneAgent Ingestion	No

Prerequisites

Dynatrace version 1.222+
For tracing, W3C Trace Context is enabled
1. From the Dynatrace menu, go to Settings > Preferences > OneAgent features.
2. Turn on Send W3C Trace Context HTTP headers.

Get the Dynatrace access details

Determine the API base URL

For details on how to assemble the base OTLP endpoint URL, see Export with OTLP. The URL should end in /api/v2/otlp.

Get API access token

The access token for ingesting traces, logs, and metrics can be generated in your Dynatrace menu under Access tokens.

Export with OTLP has more details on the format and the necessary access scopes.

Set up OpenTelemetry

Add the current versions of the following dependencies to mix.exs.

plaintext
defp deps do
  [
    {:opentelemetry_api, "~> 1.2.1"},
    {:opentelemetry, "~> 1.3.0"},
    {:opentelemetry_exporter, "~> 1.4.1"}
  ]
end

Add a release section to the application definition in mix.exs.

plaintext
releases: [
  <project_name>: [
    version: "<project_version>",
    applications: [opentelemetry_exporter: :permanent, opentelemetry: :temporary]
  ]
]

Enable the context propagation dependencies with the following line in runtime.exs.
```
plaintext
text_map_propagators: [:baggage, :trace_context],
```

Add the following configuration to config/runtime.exs and replace [URL] and [TOKEN] with the respective values for the Dynatrace URL and access token.

plaintext
import Config

config :opentelemetry,
  resource: [service: %{name: "elixir-quickstart", version: "1.0.1"}], #TODO Replace with the name and version of your application
  span_processor: :batch,
  traces_exporter: :otlp,
  resource_detectors: [
    :otel_resource_app_env,
    :otel_resource_env_var,
    ExtraMetadata
  ]

config :opentelemetry_exporter,
  otlp_protocol: :http_protobuf,
  otlp_traces_endpoint: "[URL]", #TODO Replace [URL] to your SaaS/Managed URL as mentioned in the next step
  otlp_traces_headers: [{"Authorization", "Api-Token [TOKEN]"}] #TODO Replace [TOKEN] with your API Token as mentioned in the next step

Save the following code in lib/extra_metadata.ex.

elixir
defmodule ExtraMetadata do

  @behaviour :otel_resource_detector

  def get_resource(_) do
    metadata = read_file("/var/lib/dynatrace/enrichment/dt_metadata.properties") |> unwrap_lines
    file_path = read_file("dt_metadata_e617c525669e072eebe3d0f08212e8f2.properties") |> unwrap_lines
    metadata2 = read_file(file_path) |> unwrap_lines
    attributes = get_attributes(Enum.concat(metadata, metadata2))
    :otel_resource.create(attributes)
  end

  defp unwrap_lines({:ok, metadata}), do: metadata
  defp unwrap_lines({:error, _}), do: []

  defp read_file(file_name) do
    try do
      {:ok, String.split(File.read!(file_name), "\n")}
    rescue
      File.Error ->
        {:error, "File does not exist, safe to continue"}
    end
  end

  defp get_attributes(metadata) do
    Enum.map(metadata, fn(line) ->
      if String.length(line) > 0 do
        [key, value] = String.split(line, "=")
        {key, value}
      else
        {:error, "EOF"}
      end
    end)
  end
end

Instrument your application

Add tracing

Spans are started with the macro with_span and accept an optional list of span attributes, as well as the code block for this span. The span automatically finishes when the code block returns.

elixir
require OpenTelemetry.Tracer, as: Tracer

def hello do
  Tracer.with_span "my-span", %{attributes: [{<<"my-key-1">>, <<"my-value-1">>}]} do #TODO add attributes at span creation
    Tracer.set_attributes([{"another-key-1", "another-value-1"}]) #TODO add attributes after span creation
    # Your code goes here
  end
end

Collect metrics

OpenTelemetry metrics for Elixir are under development.

Connect logs

OpenTelemetry logging for Elixir is under development.

Ensure context propagation optional

Context propagation is particularly important when network calls (for example, REST) are involved.

Extracting the context when receiving a request

To extract information on an existing context, we pass the headers to the otel_propagator_text_map.extract function, which parses the context information provided by the headers and sets the current context based on that.

elixir
#extract headers
:otel_propagator_text_map.extract(conn.req_headers)

span_ctx = OpenTelemetry.Tracer.start_span(<<"span-name">>)
ctx = OpenTelemetry.Ctx.get_current()

task = Task.async(fn ->
    OpenTelemetry.Ctx.attach(ctx)
    OpenTelemetry.Tracer.set_current_span(span_ctx)
    # do work here

    OpenTelemetry.Tracer.end_span(span_ctx)
end)

Injecting the context when sending requests

The following example uses otel_propagator_text_map:inject to provide the HTTP headers (necessary for context propagation) in merged_headers. The headers are then passed to HTTPoison.get, which allows the receiving endpoint to continue the trace with the provided information.

elixir
OpenTelemetry.Tracer.with_span "span-name" do
    ...
    # do work here
    ...
    headers = [{"content-type", "application/json"}, {"X-Custom-Header", "some-value"}]

    merged_headers = :otel_propagator_text_map.inject(headers)

    case HTTPoison.get(URL, merged_headers, []) do
        {:ok, res} -> IO.puts("Response: #{inspect(res)}")
        {:error, _} -> raise "request failed"

    end
end

Configure data capture to meet privacy requirements optional

While Dynatrace automatically captures all OpenTelemetry resource and span attributes, only attribute values specified in the allowlist are stored and displayed in the Dynatrace web UI. This prevents accidental storage of personal data, so you can meet your privacy requirements and control the amount of monitoring data stored.

To view your custom span attributes, you need to allow them in the Dynatrace web UI first.

Span attributes: In the Dynatrace menu, go to Settings and select Server-side service monitoring > Span attributes.
Resource attributes: In the Dynatrace menu, go to Settings and select Server-side service monitoring > Resource attributes.

Verify data ingestion into Dynatrace

Once you have finished the instrumentation of your application, perform a couple of test actions to create and send demo traces, metrics, and logs and verify that they were correctly ingested into Dynatrace.

To do that for traces, in the Dynatrace menu, go to Distributed traces and select the Ingested traces tab. If you use OneAgent, select PurePaths instead.

Metrics and logs can be found under their respective entries at Observe and explore.