Document cloud aggregation options. Resolve #194

src/data/markdown/translated-guides/en/02 Using k6/11 Environment variables.md

@@ -93,3 +93,41 @@ behavior of k6:
 | `K6_CLOUD_TOKEN`     | An authentication token to use in API calls to the cloud service, when the --cloud results output option is specified. |
 | `K6_NO_USAGE_REPORT` | Define this to disable [usage reports](/misc/usage-collection).                                                        |
 | `K6_OUT`             | Specify results output, same as --out command-line option.                                                             |
+
+When streaming test data to [k6 cloud](/cloud) with `k6 -o cloud`, k6 will
+collect all data and send it in batches.
+
+| Name | Description |
+| ---- | ----------- |
+| `K6_CLOUD_METRIC_PUSH_INTERVAL`               | How often to send data to the k6 cloud (default `'6s'`).                                        |
+
+k6 can also _aggregate_ the data it sends to the k6 cloud each batch.
+Aggregation is disabled by default.
+
+When using aggregation, k6 will collect incoming test data into time-buckets.
+For each data-type collected in such a bucket, it will figure out the dispersion
+(by default the [interquartile range](iqr)) around the median value. Data far
+outside the lower and upper quartiles are not aggregated, but sent as-is in
+order to not lose potentially important testing information.
+
+Aggregation is controlled by a series of environment variables you don't need to
+modify unless you have very specific statistical needs.
+
+> When running a test entirely in the cloud with `k6 cloud`, `k6` will always
+> aggregate. In this case the aggregation settings are set by the infrastructure
+> in the cloud and are not controllable from the CLI.
+
+| Name                                          | Description                                                                                              |
+|---------------------------------------------- |----------------------------------------------------------------------------------------------------------|
+| `K6_CLOUD_AGGREGATION_PERIOD`                 | >0s to activate aggregation (default disabled, `'3s'` is a good example to try) |
+| `K6_CLOUD_AGGREGATION_CALC_INTERVAL`          | How often new data will be aggregated (default `'3s'`).                                                    |
+| `K6_CLOUD_AGGREGATION_WAIT_PERIOD`            | How long to wait for period samples to accumulate before aggregating them (default `'5s'`).                |
+| `K6_CLOUD_AGGREGATION_MIN_SAMPLES`            | If fewer samples than this arrived in interval, skip aggregation (default `100`).                          |
+| `K6_CLOUD_AGGREGATION_OUTLIER_IQR_RADIUS`     | Outlier sampling from median to use for Q1 and Q3 quartiles (fraction) (default `0.25` (i.e. [IQR][iqr])). |
+| `K6_CLOUD_AGGREGATION_OUTLIER_IQR_COEF_LOWER` | How many quartiles below the lower quartile are non-aggregatable outliers (default 1.5)                            |
+| `K6_CLOUD_AGGREGATION_OUTLIER_IQR_COEF_UPPER` | How many quartiles above the upper quartile are non-aggregatable outliers (default 1.3)                            |
+
+
+
+[iqr]: https://en.wikipedia.org/wiki/Interquartile_range
+