> ## Documentation Index
> Fetch the complete documentation index at: https://docs.chronosphere.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Allow keys

export const entity_0 = "allow keys processing rule"

The allow keys [processing rule](/ingest/pipeline/processing-rules) preserves any keys
that match a specified regular expression, and then removes all other keys in
each record.

## Configuration parameters

Use the parameters in this section to configure the {entity_0}. The
Telemetry Pipeline web interface uses the items in the **Name** column to
describe these parameters. [Pipeline configuration files](/ingest/pipeline/v2/configure/config-files)
use the items in the **Key** column as YAML keys.

| Name                      | Key           | Description                                                                                                                                                                                                                                                                                                                                                                                                 | Default      |
| ------------------------- | ------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------ |
| **Regex**                 | `regex`       | Required. The regular expression that determines which keys to preserve.                                                                                                                                                                                                                                                                                                                                    | *none*       |
| **Match case** checkbox   | `matchCase`   | Indicates whether the regular expression is case-sensitive.                                                                                                                                                                                                                                                                                                                                                 | Not selected |
| **Regex engine**          | `regexEngine` | Required. The [engine](/ingest/pipeline/processing-rules#regex-engines) to parse your regular expression. Accepted values: `GNU`, `Oniguruma`, `PCRE2`, `POSIX`, `TRE`.                                                                                                                                                                                                                                     | `PCRE2`      |
| **Nested access pattern** | `nestedPath`  | The key of the highest object level to evaluate. If specified, the allow keys rule ignores any keys not contained within the specified object. If unspecified, this rule evaluates all top-level keys, but no keys nested within top-level keys. You can also use [record accessor syntax](/ingest/pipeline/processing-rules#record-accessor-syntax) to reference keys nested within another nested object. | *none*       |
| **Comment**               | `comment`     | A custom note or description of the rule's function. This text is displayed next to the rule's name in the **Actions** list in the processing rules interface.                                                                                                                                                                                                                                              | *none*       |

## Examples

Using the allow keys rule lets you pare down telemetry data by retaining only
the data you explicitly choose to keep.

### Flat example

For example, given this sample log data:

```json theme={null}
{"timestamp":"2023-03-28T09:08:41.64283645Z","user_id":3,"page_id":30,"action":"purchase"}
{"timestamp":"2023-03-28T09:08:42.643343109Z","user_id":4,"page_id":10,"action":"purchase"}
{"timestamp":"2023-03-28T09:08:48.643600498Z","user_id":1,"page_id":50,"action":"click"}
{"timestamp":"2023-03-28T09:08:50.643773688Z","user_id":5,"page_id":40,"action":"purchase"}
{"timestamp":"2023-03-28T09:08:51.643932272Z","user_id":1,"page_id":30,"action":"purchase"}
{"timestamp":"2023-03-28T09:08:56.644080944Z","user_id":2,"page_id":40,"action":"click"}
{"timestamp":"2023-03-28T09:09:03.64425954Z","user_id":3,"page_id":30,"action":"click"}
{"timestamp":"2023-03-28T09:09:03.644317046Z","user_id":1,"page_id":20,"action":"view"}
{"timestamp":"2023-03-28T09:09:10.64447719Z","user_id":2,"page_id":50,"action":"purchase"}
{"timestamp":"2023-03-28T09:09:17.644810963Z","user_id":2,"page_id":10,"action":"view"}
{"timestamp":"2023-03-28T09:09:20.644994805Z","user_id":1,"page_id":50,"action":"view"}
```

A processing rule with the **Regex** value `user` returns the following result:

```json theme={null}
{"user_id":3}
{"user_id":4}
{"user_id":1}
{"user_id":5}
{"user_id":1}
{"user_id":2}
{"user_id":3}
{"user_id":1}
{"user_id":2}
{"user_id":2}
{"user_id":1}
```

### Nested example

You can also use the allow keys rule to selectively retain information within a
nested object. For example, given this sample log data:

```json theme={null}
{"timestamp":"2023-03-28T09:08:41.64283645Z","user":{"vip":"no","id":3},"page_id":30,"action":"purchase"}
{"timestamp":"2023-03-28T09:08:42.643343109Z","user":{"vip":"yes","id":4},"page_id":10,"action":"purchase"}
{"timestamp":"2023-03-28T09:08:48.643600498Z","user":{"vip":"no","id":1},"page_id":50,"action":"click"}
{"timestamp":"2023-03-28T09:08:50.643773688Z","user":{"vip":"yes","id":5},"page_id":40,"action":"purchase"}
{"timestamp":"2023-03-28T09:08:51.643932272Z","user":{"vip":"no","id":1},"page_id":30,"action":"purchase"}
{"timestamp":"2023-03-28T09:08:56.644080944Z","user":{"vip":"yes","id":2},"page_id":40,"action":"click"}
{"timestamp":"2023-03-28T09:09:03.64425954Z","user":{"vip":"no","id":3},"page_id":30,"action":"click"}
{"timestamp":"2023-03-28T09:09:03.644317046Z","user":{"vip":"no","id":1},"page_id":20,"action":"view"}
{"timestamp":"2023-03-28T09:09:10.64447719Z","user":{"vip":"yes","id":2},"page_id":50,"action":"purchase"}
{"timestamp":"2023-03-28T09:09:17.644810963Z","user":{"vip":"yes","id":2},"page_id":10,"action":"view"}
{"timestamp":"2023-03-28T09:09:20.644994805Z","user":{"vip":"no","id":1},"page_id":50,"action":"view"}
```

A processing rule with the **Regex** value `vip` and the **Nested access pattern**
value `user` returns the following result:

```json theme={null}
{"page_id":30,"action":"purchase","timestamp":"2023-03-28T09:08:41.64283645Z","user":{"vip":"no"}}
{"page_id":10,"action":"purchase","timestamp":"2023-03-28T09:08:42.643343109Z","user":{"vip":"yes"}}
{"page_id":50,"action":"click","timestamp":"2023-03-28T09:08:48.643600498Z","user":{"vip":"no"}}
{"page_id":40,"action":"purchase","timestamp":"2023-03-28T09:08:50.643773688Z","user":{"vip":"yes"}}
{"page_id":30,"action":"purchase","timestamp":"2023-03-28T09:08:51.643932272Z","user":{"vip":"no"}}
{"page_id":40,"action":"click","timestamp":"2023-03-28T09:08:56.644080944Z","user":{"vip":"yes"}}
{"page_id":30,"action":"click","timestamp":"2023-03-28T09:09:03.64425954Z","user":{"vip":"no"}}
{"page_id":20,"action":"view","timestamp":"2023-03-28T09:09:03.644317046Z","user":{"vip":"no"}}
{"page_id":50,"action":"purchase","timestamp":"2023-03-28T09:09:10.64447719Z","user":{"vip":"yes"}}
{"page_id":10,"action":"view","timestamp":"2023-03-28T09:09:17.644810963Z","user":{"vip":"yes"}}
{"page_id":50,"action":"view","timestamp":"2023-03-28T09:09:20.644994805Z","user":{"vip":"no"}}

```

This rule retained the `vip` field within the `user` object and removed all other
fields within `user`. However, because the processing rule's scope was limited to
`user`, the rule didn't affect the `timestamp`, `page_id`, or `action` fields.

## Related rules

For a processing rule with the opposite effect, see
[block keys](/ingest/pipeline/processing-rules/block-keys).