OpenTelemetry ActionPack Instrumentation

The Action Pack instrumentation is a community-maintained instrumentation for the Action Pack portion of the Ruby on Rails web-application framework.

How do I get started?

Install the gem using:

gem install opentelemetry-instrumentation-action_pack

Or, if you use bundler, include opentelemetry-instrumentation-action_pack in your Gemfile.

Usage

To use the instrumentation, call use with the name of the instrumentation:

OpenTelemetry::SDK.configure do |c|
  c.use 'OpenTelemetry::Instrumentation::ActionPack'
end

Alternatively, you can also call use_all to install all the available instrumentation.

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

Active Support Instrumentation

Earlier versions of this instrumentation relied on patching custom dispatch hooks from Rails's Action Controller to extract request information.

This instrumentation now relies on ActiveSupport::Notifications and registers a custom Subscriber that listens to relevant events to modify the Rack span.

See the table below for details of what Rails Framework Hook Events are recorded by this instrumentation:

Event Name	Subscribe?	Creates Span?	Notes
process_action.action_controller	:white_check_mark:	:x:	It modifies the existing Rack span

Semantic Conventions

This instrumentation generally uses HTTP server semantic conventions to update the existing Rack span.

For Rails 7.1+, the span name is updated to match the HTTP method and route that was matched for the request using ActionDispatch::Request#route_uri_pattern, e.g.: GET /users/:id

For older versions of Rails the span name is updated to match the HTTP method, controller, and action name that was the target of the request, e.g.: GET /example/index

![NOTE]: Users may override the span_naming option to default to Legacy Span Naming Behavior that uses the controller's class name and action in Ruby documentation syntax, e.g. ExampleController#index.

This instrumentation does not emit any custom attributes.

Attribute Name	Type	Notes
code.namespace	String	ActionController class name
code.function	String	ActionController action name e.g. index, show, edit, etc...
http.route	String	(Rails 7.1+) the route that was matched for the request
http.target	String	The request.filtered_path

Error Handling for Action Controller

If an error is triggered by Action Controller (such as a 500 internal server error), Action Pack will typically employ the default ActionDispatch::PublicExceptions.new(Rails.public_path) as the exceptions_app, as detailed in the documentation.

The error object will be retained within payload[:exception_object]. Additionally, its storage in request.env['action_dispatch.exception'] is contingent upon the configuration of action_dispatch.show_exceptions in Rails.

Examples

Example usage can be seen in the ./example/trace_demonstration.rb file here

How can I get involved?

The opentelemetry-instrumentation-action_pack gem source is on github, along with related gems including opentelemetry-api and opentelemetry-sdk.

The OpenTelemetry Ruby gems are maintained by the OpenTelemetry Ruby special interest group (SIG). You can get involved by joining us on our GitHub Discussions, Slack Channel or attending our weekly meeting. See the meeting calendar for dates and times. For more information on this and other language SIGs, see the OpenTelemetry community page.

License

The opentelemetry-instrumentation-action_pack gem is distributed under the Apache 2.0 license. See LICENSE for more information.