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

Traces

Yes

Metrics

Logs

Prerequisites

Dynatrace version 1.222+
For tracing, W3C Trace Context is enabled
1. 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 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.

defp deps do
  [
    # Add any additional dependancies here
    {:httpoison, version: :latest},
    {:plug_cowboy, version: :latest},
    {:jason, version: :latest},
    {:plug, version: :latest},
    {:opentelemetry_exporter, version: :latest},
    {:opentelemetry_api, version: :latest},
    {:opentelemetry, version: :latest}
  ]
end

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

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

Enable the context propagation dependencies with the following line in runtime.exs.
```
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.

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,
  # Add your text map propagator from previous step here
  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.

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))
    metadata3 = read_file("/var/lib/dynatrace/enrichment/dt_host_metadata.properties") |> unwrap_lines
    attributes = get_attributes(Enum.concat(metadata, metadata2) ++ metadata3)
    :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.

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

No example yet, as OpenTelemetry for Elixir does not have stable support for metrics yet.

Connect logs

No example yet, as OpenTelemetry for Elixir does not have stable support for logs yet.

Depending on the status of the OpenTelemetry SDK, the pre-release version may nonetheless already allow the ingestion of your logs.

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.

# 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.

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 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 attributes, you need to allow them in the Dynatrace web UI first. To learn how to configure attribute storage and masking, see Attribute redaction.

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, go to Distributed Traces and select the Ingested traces tab. If you use OneAgent, select PurePaths instead.

For metrics and logs, go to Metrics or Logs or Logs & Events (latest Dynatrace).