# Example 2: A/B traffic split
<a name="monetization-functions-examples-ab"></a>

## Scenario
<a name="monetization-functions-examples-ab-scenario"></a>

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 name="monetization-functions-examples-ab-config"></a>

**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
<a name="monetization-functions-examples-ab-mapping"></a>

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

## What happens when the function runs
<a name="monetization-functions-examples-ab-runtime"></a>

1. An ad break is encountered during playback.

1. MediaTailor runs the `PRE_ADS_REQUEST` lifecycle hook and runs `abTestAdsUrl`.

1. 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](monetization-functions-types-custom-output.md), [PRE\_ADS\_REQUEST](monetization-functions-hooks-pre-ads.md), and [JSONata expression reference](monetization-functions-jsonata.md).