OpenTracing Rails Instrumentation

This gem is an attempt to introduce OpenTracing instrumentation into Rails. It’s in an early stage.

The following instrumentation is supported:

• ActionDispatch - The library introduces a rack middleware, which is intended to be used together with rack-tracer, to generate more informative operation names based on information supplied by ActionDispatch.
• ActiveRecord - The library hooks up into Rails, and instruments all ActiveRecord query.
• ActionSupport::Cache - The library hooks up into Rails, and instruments cache events.

Installation

Add this line to your application’s Gemfile:

gem 'rails-tracer'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rails-tracer

Rails::Tracer

The library hooks up into Rails using ActiveSupport::Notifications, and instruments all previously mentioned modules.
To enable instrumentation, you can either use sub-tracers directly (see sections below) or global Rails::Tracer which
will enabled all of them (except for Rack/ActionDispatch instrumentation).

Configuration Options

• tracer: OpenTracing::Tracer an OT compatible tracer. Default OpenTracing.global_tracer
• active_span: boolean an active span provider. Default: nil.
• active_record: boolean whether to enable ActiveRecord instrumentation. Default: true.
• active_support_cache: boolean whether to enable ActionDispatch::Cache instrumentation. Default: true.
  • dalli: boolean if set to true you will hook up into Dalli low-level details. Default: false.
• rack: boolean whether to enable extended Rack instrumentation. Default: false.
  • middlewares: ActionDispatch::MiddlewareStack a middlewares stack. Default: Rails.configuration.middleware.

Usage

require 'rails/tracer'
Rails::Tracer.instrument

ActionDispatch

When you use rack-tracer, the generated operation name corresponds to the request’s http method e.g. GET, POST etc.
It’s not perfect. You need to dig into the trace to understand with what url it’s related.

The rails-tracer introduces another rack middleware, which is intended to be used together with rack-tracer, to generate more informative operation names in the form ControllerName#action.

Usage

require 'rack/tracer'
require 'rails/tracer'
Rails.configuration.middleware.use(Rack::Tracer)
Rails.configuration.middleware.insert_after(Rack::Tracer, Rails::Rack::Tracer)

or simpler

Rails::Rack::Tracer.instrument

optionally you can pass tracer argument to instrument method.

ActiveRecord

The library hooks up into Rails using ActiveSupport::Notifications, and instruments all ActiveRecord query.

Usage

Auto-instrumentation example.

require 'rails/tracer'
ActiveRecord::Tracer.instrument(tracer: OpenTracing.global_tracer,
                               active_span: -> { OpenTracing.global_tracer.active_span })

There are times when you might want to skip ActiveRecord’s magic, and use connection directly. Still the library
can help you with span creation. Instead of auto-instrumenting you can manually call ActiveRecord::Tracer.start_span as shown below.

def q(name, sql)
  span = ActiveRecord::Tracer.start_span(name, 
                                          tracer: OpenTracing.global_tracer,
                                          active_span: -> { OpenTracing.global_tracer.active_span },
                                          sql: sql)
  ActiveRecord::Base.
    connection.
    raw_connection.
    query(sql).
    each(as: :hash)
ensure
  span&.finish
end
q("FirstUser", "SELECT * FROM users LIMIT 1")

ActiveSupport::Cache

The library hooks up into Rails using ActiveSupport::Notifications, and instruments all ActiveSupport::Cache events.

Usage

Auto-instrumentation example.

require 'rails/tracer'
ActiveSupport::Cache::Tracer.instrument(tracer: OpenTracing.global_tracer, 
                                        active_span: -> { OpenTracing.global_tracer.active_span })

If you use Dalli and ActiveSupport::DalliStore as your application’s cache store, you can get low-level details about Memcached calls by setting dalli option to true. If you want to get even more details, simply require tracing-logger and Dalli error logs will be attached to the current active span. The library will wrap current Dalli.logger into a Tracing::CompositeLogger and append additional Tracing::Logger with severity level set to Logger::ERROR.

ActiveSupport::Cache::Tracer.instrument(tracer: OpenTracing.global_tracer, 
                                        active_span: -> { OpenTracing.global_tracer.active_span },
                                        dalli: true)

If you want to skip the auto-instrumentation, still the library can help you with span creation and setting up proper tags. Instead of auto-instrumenting, as shown above, you can manually call ActiveSupport::Tracer.start_span as shown below.

def read(key)
  span = ActiveSupport::Cache::Tracer.start_span("InMemoryCache#read", 
                                                 tracer: OpenTracing.global_tracer,
                                                 active_span: -> { OpenTracing.global_tracer.active_span },
                                                 key: key)
  result = in_memory_cache[key]
  span.set_tag('cache.hit', !!result) 
  result
ensure
  span&.finish
end
read("user-1")

Development

After checking out the repo, install dependencies.

bundle install
appraisal install

The tests depends on having memcached running locally within docker container. It means you need to install docker, and docker-compose first.
Once you’re done to run the containers:

docker-compose up -d

Then, to run tests for all appraisals:

appraisal bundle exec rspec spec

You can also run bin/console for an interactive prompt that will allow you to experiment.

To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/iaintshine/ruby-rails-tracer. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.