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

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.

HTTP semantic convention stability

In the OpenTelemetry ecosystem, HTTP semantic conventions have now reached a stable state. However, the initial Rack instrumentation, which Action Pack relies on, was introduced before this stability was achieved, which resulted in HTTP attributes being based on an older version of the semantic conventions.

To facilitate the migration to stable semantic conventions, you can use the OTEL_SEMCONV_STABILITY_OPT_IN environment variable. This variable allows you to opt-in to the new stable conventions, ensuring compatibility and future-proofing your instrumentation.

Sinatra instrumentation installs Rack middleware, but the middleware version it installs depends on which OTEL_SEMCONV_STABILITY_OPT_IN environment variable is set.

When setting the value for OTEL_SEMCONV_STABILITY_OPT_IN, you can specify which conventions you wish to adopt:

http - Emits the stable HTTP and networking conventions and ceases emitting the old conventions previously emitted by the instrumentation.
http/dup - Emits both the old and stable HTTP and networking conventions, enabling a phased rollout of the stable semantic conventions.
Default behavior (in the absence of either value) is to continue emitting the old HTTP and networking conventions the instrumentation previously emitted.

During the transition from old to stable conventions, Rack instrumentation code comes in three patch versions: dup, old, and stable. These versions are identical except for the attributes they send. Any changes to Rack instrumentation should consider all three patches.

For additional information on migration, please refer to our documentation.