Table of contents

Ruby on Rails

This guide will help you instrument your Ruby on Rails application(s) with OpenTelemetry and send traces to Checkly.

Although this guide is for Ruby on Rails, the steps are largely the same as instrumenting any Ruby application with OpenTelemetry. This guide assumes you have a basic understanding of Ruby on Rails and already have a working Rails application.

Go to the root of your Rails app and add the basic OpenTelemetry SDK, OTLP exporter and instrumentation gems to your Gemfile:

bundle add opentelemetry-sdk \
opentelemetry-exporter-otlp \
opentelemetry-instrumentation-all

This should add the following lines:

# Gemfile
gem "opentelemetry-sdk", "~> 1.4"
gem "opentelemetry-exporter-otlp", "~> 0.26.3"
gem "opentelemetry-instrumentation-all", "~> 0.60.0"

As per the Ruby on Rails convention, we add an instrumentation.rb file to the config/initializers directory.

# config/initializers/instrumentation.rb

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

class ChecklySampler

    def should_sample?(trace_id:, parent_context:, links:, name:, kind:, attributes:)
      tracestate = OpenTelemetry::Trace.current_span(parent_context).context.tracestate
      decision = tracestate.value('checkly') ? OpenTelemetry::SDK::Trace::Samplers::Decision::RECORD_AND_SAMPLE : 
        OpenTelemetry::SDK::Trace::Samplers::Decision::DROP
      puts(decision)  
      OpenTelemetry::SDK::Trace::Samplers::Result.new(decision: decision, attributes: {}, tracestate: tracestate)
    end
  
    def description
      'ChecklySampler'
    end
  end

OpenTelemetry::SDK.configure do |c|
  c.use_all()
end

OpenTelemetry.tracer_provider.sampler = ChecklySampler.new

Notice the ChecklySampler configuration. This is a custom, head-based sampler that will only sample spans that are generated by Checkly by inspecting the trace state. This way you only pay for the egress traffic generated by Checkly and not for any other traffic. Also note that the use_all() method will automatically install all available instrumentation libraries.

First, make sure to switch on the Basic HTTP Instrumentation. This will add the necessary headers to your HTTP requests.

Then, toggle on Send Traces, grab your OTel API key in the OTel API keys section of the Open Telemetry Integration page in the Checkly app and take a note of the endpoint for the region you want to use.

Now, export your API key in your shell by setting the OTEL_EXPORTER_OTLP_HEADERS environment variable.

export OTEL_EXPORTER_OTLP_HEADERS="authorization=<your-api-key>"

Next, export the endpoint for the region you want to use and give your service a name.

export OTEL_EXPORTER_OTLP_ENDPOINT="https://otel.eu-west-1.checklyhq.com"
export OTEL_SERVICE_NAME="your-service-name"

We are using the standard OpenTelemetry environment variables here to configure the OTLP exporter.

You can now restart your Rails app with the instrumentation enabled.

rails server

If you run into any issues, you can also output any traces to the console as follows:

env OTEL_TRACES_EXPORTER=console rails server

Similarly, you can set the OTEL_LOG_LEVEL environment variable to DEBUG to get more detailed logs.

env OTEL_LOG_LEVEL=DEBUG rails server

• https://opentelemetry.io/docs/languages/ruby/getting-started/

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Last updated on June 7, 2024. You can contribute to this documentation by editing this page on Github