# Set Up Tracing | Sentry for Rack Middleware

With [tracing](https://docs.sentry.io/product/insights/overview.md), Sentry tracks your software performance, measuring metrics like throughput and latency, and displaying the impact of errors across multiple systems. Sentry captures distributed traces consisting of transactions and spans, which measure individual services and individual operations within those services. Learn more about our model in [Distributed Tracing](https://docs.sentry.io/product/sentry-basics/tracing/distributed-tracing.md).

If you’re adopting Tracing in a high-throughput environment, we recommend testing prior to deployment to ensure that your service’s performance characteristics maintain expectations.

Sentry can integrate with **OpenTelemetry**. You can find more information about it [here](https://docs.sentry.io/platforms/ruby/guides/rack/tracing/instrumentation/opentelemetry.md).

## [Configure](https://docs.sentry.io/platforms/ruby/guides/rack/tracing.md#configure)

First, enable tracing and configure the sample rate for transactions. Set the sample rate for your transactions by either:

* Setting a uniform sample rate for all transactions using the `traces_sample_rate` option in your SDK config to a number between `0` and `1`. (For example, to send 20% of transactions, set `traces_sample_rate` to `0.2`.)
* Controlling the sample rate based on the transaction itself and the context in which it's captured, by providing a function to the `traces_sampler` config option.

The two options are meant to be mutually exclusive. If you set both, `traces_sampler` will take precedence.

Tracing is available for our updated Ruby SDK (`sentry-ruby`, not `sentry-raven`).

```ruby
Sentry.init do |config|
  #...

  # Set a uniform sample rate between 0.0 and 1.0
  # We recommend adjusting the value in production:
  config.traces_sample_rate = 1.0

  # or control sampling dynamically
  config.traces_sampler = lambda do |sampling_context|
    # sampling_context[:transaction_context] contains the information about the transaction
    # sampling_context[:parent_sampled] contains the transaction's parent's sample decision
    true # return value can be a boolean or a float between 0.0 and 1.0
  end
end
```

Learn more about tracing [options](https://docs.sentry.io/platforms/ruby/guides/rack/configuration/options.md#tracing-options), how to use the [traces\_sampler](https://docs.sentry.io/platforms/ruby/guides/rack/configuration/sampling.md#setting-a-sampling-function) function, or how to [sample transactions](https://docs.sentry.io/platforms/ruby/guides/rack/configuration/sampling.md#sampling-transaction-events).

## [Verify](https://docs.sentry.io/platforms/ruby/guides/rack/tracing.md#verify)

Test out tracing by starting and finishing a transaction, which you *must* do so transactions can be sent to Sentry. Learn how in our [Custom Instrumentation](https://docs.sentry.io/platforms/ruby/guides/rack/tracing/instrumentation/custom-instrumentation.md) content.

While you're testing, set `traces_sample_rate` to `1.0`, as that ensures that every transaction will be sent to Sentry. Once testing is complete, you may want to set a lower `traces_sample_rate` value, or switch to using `traces_sampler` to selectively sample and filter your transactions, based on contextual data.

## [Next Steps](https://docs.sentry.io/platforms/ruby/guides/rack/tracing.md#next-steps)

* #### [Instrumentation](https://docs.sentry.io/platforms/ruby/guides/rack/tracing/instrumentation.md)

  Learn how to instrument tracing in your app.

* #### [Trace Propagation](https://docs.sentry.io/platforms/ruby/guides/rack/tracing/trace-propagation.md)

  Learn how to connect events across applications/services.

## Pages in this section

- [Instrumentation](https://docs.sentry.io/platforms/ruby/guides/rack/tracing/instrumentation.md)
- [Trace Propagation](https://docs.sentry.io/platforms/ruby/guides/rack/tracing/trace-propagation.md)
