docs: adds RoR docs + tweaks [sc-00]

site/content/docs/open-telemetry/instrumenting-code/_index.md

@@ -56,13 +56,6 @@ Below you will find instructions on how to instrument your popular languages and
 	img="/docs/images/integrations/otel/otel-languages/go_icon.svg"
 	link="/docs/open-telemetry/instrumenting-code/go/"
 >}}
-{{< doc-card
-	class="three-column-card"
-	headerTag="h3"
-	title="Ruby"
-	img="/docs/images/integrations/otel/otel-languages/ruby_icon.svg"
-	link="/docs/open-telemetry/instrumenting-code/ruby/"
->}}
 </div>
 <br>
 
@@ -86,9 +79,9 @@ Below you will find instructions on how to instrument your popular languages and
 {{< doc-card
 	class="three-column-card"
 	headerTag="h3"
-	title=".NET"
-	img="/docs/images/integrations/otel/otel-languages/dot-net_icon.svg"
-	link="/docs/open-telemetry/instrumenting-code/dot-net/"
+	title="Ruby on Rails"
+	img="/docs/images/integrations/otel/otel-languages/ruby_on_rails_icon.svg"
+	link="/docs/open-telemetry/instrumenting-code/ruby-on-rails/"
 >}}
 </div>
 <br>

site/content/docs/open-telemetry/instrumenting-code/express.md

@@ -1,6 +1,11 @@
 ---
 title: Express
 weight: 38
+head:
+  title: "Instrumenting Express.js with OpenTelemetry"
+metatags:
+  title: "Instrumenting Express.js with OpenTelemetry"
+  description: "Instrument your Express.js application with OpenTelemetry and send traces to Checkly."
 menu:
   integrations:
     parent: "Instrumenting your code with OpenTelemetry"

site/content/docs/open-telemetry/instrumenting-code/ruby-on-rails.md

@@ -0,0 +1,101 @@
+---
+title: Ruby on Rails
+weight: 36
+head:
+  title: "Instrumenting Ruby on Rails with OpenTelemetry"
+metatags:
+  title: "Instrumenting Ruby on Rails with OpenTelemetry"
+  description: "Instrument your Ruby on Rails application with OpenTelemetry and send traces to Checkly."
+menu:
+  integrations:
+    parent: "Instrumenting your code with OpenTelemetry"
+beta: true
+---
+
+This guide will help you instrument your Ruby on Rails application(s) with OpenTelemetry and send traces to Checkly.
+<!--more-->
+Although this guide is for [Ruby on Rails](https://rubyonrails.org/), the steps are largely the same as instrumenting 
+any Ruby application with OpenTelemetry. This guide assumes you have a basic understanding of Ruby on Rails and already 
+have a working Rails application.
+
+## Step 1: Install the OpenTelemetry package
+
+Go to the root of your Rails app and add the basic OpenTelemetry SDK, OTLP exporter and instrumentation gems to your Gemfile:
+
+```bash
+bundle add opentelemetry-sdk \
+opentelemetry-exporter-otlp \
+opentelemetry-instrumentation-all
+```
+
+This should add the following lines:
+```ruby
+# Gemfile
+gem "opentelemetry-sdk", "~> 1.4"
+gem "opentelemetry-exporter-otlp", "~> 0.26.3"
+gem "opentelemetry-instrumentation-all", "~> 0.60.0"
+```
+
+## Step 2: Initialize the instrumentation
+
+As per the Ruby on Rails convention, we add an `instrumentation.rb` file to the `config/initializers` directory.
+
+```ruby
+# config/initializers/instrumentation.rb
+
+require 'opentelemetry/sdk'
+require 'opentelemetry/instrumentation/all'
+
+class ChecklySampler
+
+    def should_sample?(trace_id:, parent_context:, links:, name:, kind:, attributes:)
+      tracestate = OpenTelemetry::Trace.current_span(parent_context).context.tracestate
+      decision = tracestate.value('checkly') ? OpenTelemetry::SDK::Trace::Samplers::Decision::RECORD_AND_SAMPLE : 
+        OpenTelemetry::SDK::Trace::Samplers::Decision::DROP
+      puts(decision)  
+      OpenTelemetry::SDK::Trace::Samplers::Result.new(decision: decision, attributes: {}, tracestate: tracestate)
+    end
+
+    def description
+      'ChecklySampler'
+    end
+  end
+
+OpenTelemetry::SDK.configure do |c|
+  c.use_all()
+end
+
+OpenTelemetry.tracer_provider.sampler = ChecklySampler.new
+```
+Notice the `ChecklySampler` configuration. This is a custom, **head-based sampler** that will only sample spans that 
+are generated by Checkly by inspecting the trace state. This way you only pay for the egress traffic generated by Checkly 
+and not for any other traffic. Also note that the `use_all()` method will automatically install all available 
+instrumentation libraries.
+
+## Step 3: Start your app with the instrumentation
+
+{{< markdownpartial "/_shared/otel-api-and-endpoint.md" >}}
+
+You can now restart your Rails app with the instrumentation enabled.
+
+```bash
+rails server
+```
+
+## Debugging and troubleshooting
+
+If you run into any issues, you can also output any traces to the console as follows:
+
+```bash
+env OTEL_TRACES_EXPORTER=console rails server
+```
+
+Similarly, you can set the `OTEL_LOG_LEVEL` environment variable to `DEBUG` to get more detailed logs.
+
+```bash
+env OTEL_LOG_LEVEL=DEBUG rails server
+```
+
+## Further reading
+
+- [https://opentelemetry.io/docs/languages/ruby/getting-started/](https://opentelemetry.io/docs/languages/ruby/getting-started/)