opentracing_rails - Unleashing opentracing for Rails

Distributed tracing instrumentation for Ruby on Rails applications based on Opentracing standard.

Installation

Add this line to your application's Gemfile:

gem 'opentracing_rails'

This gem is based on Opentracing standard but is not bound to any implementation of it. Therefore, you need to choose which implementation want to use.

Once you have chosen the backend, add the following lines into an initializer specifying it:

Jaeger

For instance, the CNCF project Jaeger and its ruby implementation jaeger-client-ruby.

# config/initializers/opentracing.rb

require 'jaeger/client'

OpenTracing.global_tracer = Jaeger::Client.build(
  service_name: Rails.application.class.parent_name,
  host: 'localhost',
  port: 6831)

Zipkin

An alternative to Jaeger, there is Zipkin which has its ruby implementation zipking-ruby-opentracing.

# config/initializers/opentracing.rb

require 'zipkin/tracer'
OpenTracing.global_tracer = Zipkin::Tracer.build(
  url: 'http://localhost:9411',
  service_name: Rails.application.class.parent_name)

Environment preparation

For running a Jaeger instance, you can use the official All-in-one docker image they provide for testing purposes. Within this image, also, you can find running the Jaeger UI running on http://localhost:16686.

The simplest way to start the all in one docker image is to use the pre-built image published to DockerHub (a single command line).

docker run -d -e COLLECTOR_ZIPKIN_HTTP_PORT=9411 -p5775:5775/udp -p6831:6831/udp -p6832:6832/udp \
  -p5778:5778 -p16686:16686 -p14268:14268 -p9411:9411 jaegertracing/all-in-one:latest

Usage

current_span

OpenTracing::Rails defines a current_span method which tells the whole trace information collected until the moment. TODO: more info, if needed. maybe classname?

Tracking http communications

TODO: section aim description

conn = Faraday.new(url: 'http://localhost:3001/') do |faraday|
  faraday.use Faraday::Tracer, span: current_span

  faraday.request :url_encoded
  faraday.adapter Faraday.default_adapter
end

p conn.get('/').body

Tracing special operations

TODO: explain how to create a new span inside the current trace. smth like that:

span = @tracer.start_span('interesting_transaction,
  child_of: parent_span,
  tags: {
    'component' => 'faraday',
    'span.kind' => 'client',
    'http.method' => 'GET'
    'http.url' => 'internal'
  }
)

# do all the interesting things here

span.finish

Tracing ActiveRecord

OpenTracing::Rails traces all ActiveRecord transactions by default, without any configuration. There are some options that can be set, though:

• skip_schema_queries: Avoid adding to the trace internal AR queries for schema, to not pollute the trace. Default: true.

Draft tasks to do in future

• Avoid changing config.ru for adding use Rack::Tracer
• Add ActiveRecord tracer within a middleware
• Add Sidekiq support
• Set railsy names to traces (for better understanding on Opentracing backend)