Overview

When instrumenting a RUM application, you can remotely control the RUM initialization configurations based on your immediate needs, such as an ongoing incident where you might need higher fidelity data.

Instead of having to deploy the changes to your RUM initialization configurations, you can use feature flags. Feature flag management companies like LaunchDarkly evaluate feature flags on the server side and thus allow you to make changes to your code without needing to redeploy it.

Setting up your flag in LaunchDarkly

To set up your flag in LaunchDarkly, start by following their documentation on setting up an SDK. For additional details, see LaunchDarkly’s Client-side SDK documentation.

LaunchDarkly supports multivariate flags, which lets you customize the number and types of variations they return. Multivariate flag types include:

• String flags: Frequently used to pass simple configuration values or even content.
• Number flags: Frequently used to pass simple numeric configuration values.
• JSON flags: Can be used to pass complex configuration objects or even structured content.

Feature flag options

This guide covers two ways you can set up your feature flags to modify your RUM configuration remotely:

1. Create a feature flag for each individual parameter you’d like to configure.
2. Create a feature flag for the entire RUM configuration.

Tip: Using the first option to create individual flags for each parameter can give you more fine-grained control over your RUM configuration. Creating a feature flag for the entire RUM configuration may result in lots of different variants that can be harder to keep track of and cause overhead for your developers to determine what the specific differences between the variants are.

Individual parameter option

In the example below, a feature flag for an individual parameter, sessionSampleRate, of the RUM Configuration is created.

1. Create a new feature flag in LaunchDarkly and provide a name, and key.

2. Specify the flag variations. For the sessionSampleRate parameter, you’ll want to pass a number value, so you can choose the flag type to be Number and add the Sample Rates you would like as the value in the variation fields.

   Note: You can create multiple different flag variations if you’d like. Don’t worry about adding all the possible sample rates that you might want now. You can always add a new variation of values later.

3. Set your default rules. In the example below, the “Default Sample Rate” is set when the feature flag is off and the “High Fidelity Sample Rate” when the feature flag is on.

Entire RUM configuration option

In this example, a feature flag for the entire RUM Configuration Object is created.

1. Create a new feature flag in LaunchDarkly and provide a name, and key.

2. Modify the Flag Variations. For the RUM configuration, you’ll want to pass an Object, so you can choose the flag type to be JSON, add the configurations you’d like as the values, and modify the JSON to an Object in our code later.

   Note: You can create multiple different flag variations if you’d like. Don’t worry about adding all possible configurations that you might want, you can always go in and add a new variation of values whenever you want.

3. Set your default rules. The “Default Configuration” is set when the feature flag is off and the “High Fidelity Configuration” when the feature flag is on.

Adding your feature flag to your RUM configuration

Once you’ve got set up with LaunchDarkly as mentioned above, installed the dependencies, and initialized the LaunchDarkly client ), you can add the feature flag evaluation into Datadog’s code. You can read more about evaluating flags in LaunchDarkly here.

Individual parameter option

Before you initialize the RUM SDK for an individual parameter, you need to first evaluate your LaunchDarkly feature flags.

In this example, you can add an evaluation in JS like the code snippet below.

const RUM_sample_rate = client.variation('rum-sample-rate-configuration', false);

Then add this to your RUM initialization:

datadogRum.init({
  applicationId: '<DATADOG_APPLICATION_ID>',
  clientToken: '<DATADOG_CLIENT_TOKEN>',
  site: '<DATADOG_SITE>',
  service: 'my-web-application',
  env: 'production',
  version: '1.0.0',
  sessionSampleRate: RUM_sample_rate,
  sessionReplaySampleRate: 100,
  trackResources: true,
  trackLongTasks: true,
  trackUserInteractions: true,
})

Entire RUM configuration option

Before you initialize the RUM SDK, you need to first evaluate your LaunchDarkly feature flags. For example, in JS you can add an evaluation like this:

const RUM_configuration = client.variation('rum-configuration', false);

However, before you can pass in the configuration to initialize RUM, you’ll need to create an Object from the flag JSON value. Once you’ve done that, you can initialize the RUM SDK.

datadogRum.init(RUM_configuration_object)

Embed LaunchDarkly’s controls to configure RUM directly in your Dashboards

If you want to change your RUM configuration directly in your Datadog application, you can embed the LaunchDarkly UI into Datadog and switch your feature flag on/off. The feature flags are set up so you can keep them off, with the default values. When you want to have higher fidelity data, you can turn on your feature flag and the values you set for the ON variation are used for the RUM initialization.

LaunchDarkly’s Datadog App integration embeds the feature flag management UI as a dashboard widget. You can use this widget to toggle feature flags without ever leaving Datadog. You can embed the LaunchDarkly widget within a new or existing dashboard that displays key metrics. If there is an incident or spike in errors, you can toggle the feature flag for your RUM configuration from within Datadog to begin sampling more data and ensuring your teams have access to the information they need to address and resolve your issue.

If you need to change the values that you originally set for your configuration, you can update your flag within LaunchDarkly at any time. After you save your changes, all new flag evaluations have your updated values.

Further Reading

Documentation, liens et articles supplémentaires utiles:

Visualize your RUM data in the RUM ExplorerDOCUMENTATION