opentelemetry-instrumentation-rack

OpenTelemetry Rack Instrumentation

The Rack instrumentation is a community-maintained instrumentation for the Rack web server interface.

How do I get started?

Install the gem using:

gem install opentelemetry-instrumentation-rack

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

Version Compatibility

Older versions of Rack are not supported by the latest version of this instrumentation. If you are using an older version of Rack and need an earlier version of this instrumentation, then consider installing and pinning the compatible gem version, e.g.:

gem opentelemetry-instrumentation-rack, "<version>"

Rack Version	Instrumentation Version
< 2.0	= 0.22.1
>= 2.0	~> 0.23

Usage

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

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

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

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

Rack Middleware vs Rack Events

Since v0.24.0, this instrumentation uses Rack::Events as opposed to Middleware to support Requests that use Buffered Response Bodies.

If your application does not support Rack::Events, you may disable it by setting use_rack_events: false, e.g.

OpenTelemetry::SDK.configure do |c|
  c.use 'OpenTelemetry::Instrumentation::Rack', use_rack_events: false
end

This will switch to using Rack::Middleware by default in dependent instrumentations.

See #342 for more details.

Controlling span name cardinality

By default we will set the rack span name to match the format "HTTP #{method}" (ie. HTTP GET). There are different ways to control span names with this instrumentation.

Enriching rack spans

We surface a hook to easily retrieve the rack span within the context of a request so that you can add information to or rename your server span.

This is how the rails controller instrumentation is able to rename the span names to match the controller and action that process the request. See https://github.com/open-telemetry/opentelemetry-ruby-contrib/blob/opentelemetry-instrumentation-action_pack/v0.9.0/instrumentation/action_pack/lib/opentelemetry/instrumentation/action_pack/handlers/action_controller.rb#L29 for an example.

High cardinality example

You can pass in an url quantization lambda that simply uses the URL path, the result is you will end up with high cardinality span names, however this may be acceptable in your deployment and is easy configurable using the following example.

OpenTelemetry::SDK.configure do |c|
  c.use 'OpenTelemetry::Instrumentation::Rack', { url_quantization: ->(path, _env) { path.to_s } }
end

Examples

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

How can I get involved?

The opentelemetry-instrumentation-rack 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-rack 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 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.

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.