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Example 2: A/B traffic split - AWS Elemental MediaTailor
ScenarioConfigurationFunction mappingWhat happens when the function runs

Example 2: A/B traffic split

Scenario

A streaming service wants to use a CUSTOM_OUTPUT function to randomly split ad request traffic between two ad decision server (ADS) URLs for A/B testing. Half of the ad requests go to the v1 endpoint and half go to the v2 endpoint.

Configuration

A/B traffic split (CUSTOM_OUTPUT):

{
    "FunctionId": "abTestAdsUrl",
    "FunctionType": "CUSTOM_OUTPUT",
    "CustomOutputConfiguration": {
        "Runtime": "JSONATA",
        "Output": {
            "adsRequest.url": "{%$random() < 0.5 ? 'https://ads.example.com/v1/decision?session=' & session.id : 'https://ads.example.com/v2/decision?session=' & session.id%}"
        }
    }
}

In this configuration:

  • FunctionId — A unique name for this function.

  • FunctionType — CUSTOM_OUTPUT evaluates expressions without making HTTP calls.

  • Output — Maps adsRequest.url to an expression that randomly selects one of two ADS URLs.

Function mapping

{
    "FunctionMapping": {
        "PRE_ADS_REQUEST": "abTestAdsUrl"
    }
}

What happens when the function runs

  1. An ad break is encountered during playback.

  2. MediaTailor runs the PRE_ADS_REQUEST lifecycle hook and runs abTestAdsUrl.

  3. The $random() function returns a value between 0 and 1. If the value is less than 0.5, the function sets the ADS URL to the v1 endpoint. Otherwise, it sets the URL to the v2 endpoint.

The $random() function is evaluated on each ad break, so the split is per ad request, not per session.

Tip

To adjust the traffic split ratio, change the threshold value. For example, $random() < 0.8 sends 80% of traffic to the first URL and 20% to the second.

Note

Writing to adsRequest.url overrides the default ADS URL configured in the playback configuration for the current ad break.

For more information, see CUSTOM_OUTPUT, PRE_ADS_REQUEST, and JSONata expression reference.