Experimenter Configuration

The structure of this configuration is a key-value collection with the full metric identification of the Glean metric serving as the key in the format <metric_category.metric_name>.

The values of the key-value pair are booleans which represent whether the metric is enabled (true) or not (false).

In the example below gleanMetricConfiguration is the name of the variable defined in the Nimbus feature.

This configuration would be what is entered into the branch configuration setup in Experimenter when defining an experiment or rollout.

Example Configuration:

{
  "gleanMetricConfiguration": {
    "metrics_enabled": {
      "urlbar.abandonment": true,
      "urlbar.engagement": true,
      "urlbar.impression": true
    }
  }
}

Server Knobs Configuration in Pings

When Server Knobs configuration is applied through applyServerKnobsConfig, the entire configuration is automatically recorded as an ObjectMetric and included in the ping_info section of all pings except for those with metadata.include_info_sections: false.

This makes it easier to identify which metrics are being controlled by Server Knobs and to calculate effective sampling rates in analysis.

The configuration is stored using a standard ObjectMetric (at glean.internal.metrics.server_knobs_config), which provides schema definition support for downstream tooling and requires minimal changes to ingestion pipeline schemas.

How It Appears in Pings

The complete Server Knobs configuration is included in ping_info.server_knobs_config:

{
  "ping_info": {
    "seq": 123,
    "start_time": "2024-01-01T00:00:00Z",
    "end_time": "2024-01-01T01:00:00Z",
    "server_knobs_config": {
      "metrics_enabled": {
        "urlbar.engagement": true,
        "urlbar.impression": true
      }
    }
  },
  "metrics": {
    "counter": {
      "urlbar.engagement": 5,
      "urlbar.impression": 2
    }
  }
}