Send OpenTelemetry from Rails to your Mac

Ruby instruments Rails, the HTTP clients, and the database from one initializer.

Before you start

• Loggerhead is open.
• You know the effective port. Open Collectors → Loggerhead receiver → Connection and copy the HTTP port. The first workspace uses 4318. See Ports and the effective port.

Step 1: add the gems

Gemfile

gem 'opentelemetry-sdk'
gem 'opentelemetry-exporter-otlp'
gem 'opentelemetry-instrumentation-all'

Then run bundle install.

Step 2: write the initializer

config/initializers/opentelemetry.rb

require 'opentelemetry/sdk'
require 'opentelemetry/instrumentation/all'

OpenTelemetry::SDK.configure do |c|
  c.service_name = 'my-rails-app'
  c.use_all
end

Step 3: set the endpoint

.env

OTEL_EXPORTER_OTLP_ENDPOINT=http://127.0.0.1:4318

The Ruby exporter speaks HTTP with protobuf and needs no protocol setting.

Start the server with bin/rails server and open one page.

What arrives

Signal	State
Traces	Every request, with the controller, the view, and each SQL statement.
Metrics	Only what you record yourself. The Ruby metrics SDK is young.
Logs	Not from these gems. Send the Rails log through a branch collector. See Docker branch example.

Tag the environment

OTEL_RESOURCE_ATTRIBUTES=deployment.environment.name=staging

See Workspaces and environments.

Then read it with your agent

1. Open Traces in Loggerhead and click a request to open its waterfall.
2. Connect your coding agent once, and it reads the same data. See Claude Code.