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Elixir Phoenix

Implement OpenTelemetry instrumentation for Phoenix applications to collect traces; monitor HTTP requestsand database queries using the Elixir OTel SDK.

Note: This guide provides a concise overview based on the official OpenTelemetry documentation. For complete information, please consult the official OpenTelemetry documentation.

Overview​

This guide walks through setting up automatic OpenTelemetry instrumentation for Phoenix applications, including HTTP request tracing, database query monitoring with Ecto, and log correlation. The instrumentation automatically exports telemetry data to Scout Collector for visualization.

Prerequisites​

Before starting, ensure you have:

  • Elixir 1.13 or later installed
  • Phoenix application set up
  • Access to package installation (Mix)
  • Scout collector endpoint

Required Packages​

Install the following necessary packages by adding them to mix.exs and running mix deps.get.

mix.exs
defp deps do
  [
    # OpenTelemetry core packages
    {:opentelemetry, "~> 1.3"},
    {:opentelemetry_exporter, "~> 1.6"},

    # Automatic instrumentation for Phoenix and Ecto
    {:opentelemetry_phoenix, "~> 1.1"},
    {:opentelemetry_ecto, "~> 1.1"}
  ]
end

After adding the dependencies, install them:

mix deps.get

Traces​

Traces give us the big picture of what happens when a request is made to an application. Whether your application is a monolith with a single database or a sophisticated mesh of services, traces are essential to understanding the full "path" a request takes in your application.

Auto Instrumentation of Traces​

Step 1: Initialize OpenTelemetry Instrumentation​

Add the following setup calls in your application module's start/2 function:

lib/phoenix_app/application.ex
def start(_type, _args) do
  # Initialize Phoenix instrumentation
  OpentelemetryPhoenix.setup()

  # Initialize Ecto instrumentation
  OpentelemetryEcto.setup([:phoenix_app, :repo])

  # ... rest of your application setup
end

Step 2: Configure OpenTelemetry Exporter​

Add OpenTelemetry configuration to your runtime configuration:

config/runtime.exs
import Config

# OpenTelemetry resource configuration
config :opentelemetry,
  resource: [
    service: [
      name: "phoenix-app",
      version: "1.0.0"
    ]
  ]

# OpenTelemetry exporter configuration
config :opentelemetry_exporter,
  otlp_protocol: :http_protobuf,
  otlp_endpoint: "http://localhost:4318"

Replace localhost:4318 with your Scout collector endpoint.

Official Traces Documentation

Step 3: Configure Logger with Trace Context​

Add trace context to your logs for correlation:

config/config.exs
config :logger, :default_formatter,
  format: "$time [$level] $message trace_id=$otel_trace_id span_id=$otel_span_id\n",
  metadata: [:otel_trace_id, :otel_span_id]

View these traces in base14 Scout observability backend.

That's it! Head over to Scout Grafana to visualize the traces.

References​

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