[8.x] [8.17] Document impact of using logsDB for security users (back…

…port #6272) (#6304)

* [8.17] Document impact of using logsDB for security users (#6272)

* First draft

* Removes serverless content

* Minor change

* Removes unnecessary words

* Fixes casing for all mentions of logsdb

ESS and Serverless

* Update docs/detections/detections-logsdb-impact.asciidoc

Co-authored-by: natasha-moore-elastic <[email protected]>

* Update docs/detections/detections-logsdb-impact.asciidoc

Co-authored-by: natasha-moore-elastic <[email protected]>

* Update docs/serverless/rules/detections-logsdb-impact.asciidoc

Co-authored-by: natasha-moore-elastic <[email protected]>

* Update docs/serverless/rules/detections-logsdb-impact.asciidoc

Co-authored-by: natasha-moore-elastic <[email protected]>

* Adds licensing info

---------

Co-authored-by: natasha-moore-elastic <[email protected]>
(cherry picked from commit 61b1f1b)

# Conflicts:
#	docs/serverless/rules/detection-engine-overview.asciidoc
#	docs/serverless/rules/detections-logsdb-impact.asciidoc

* Delete docs/serverless directory and its contents

---------

Co-authored-by: Nastasha Solomon <[email protected]>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

docs/detections/detection-engine-intro.asciidoc

@@ -167,3 +167,9 @@ and you should contact your {kib} administrator.
 NOTE: For *self-managed* {stack} deployments only, this message may be
 displayed when the <<detections-permissions, `xpack.security.enabled`>>
 setting is not enabled in the `elasticsearch.yml` file. For more information, refer to <<detections-on-prem-requirements>>.
+
+[discrete]
+[[detections-logsdb-index-mode]]
+== Using logsdb index mode 
+
+To learn how your rules and alerts are affected by using the {ref}/logs-data-stream.html[logsdb index mode], refer to <<detections-logsdb-index-mode-impact>>. 

docs/detections/detections-index.asciidoc

@@ -2,6 +2,8 @@ include::detection-engine-intro.asciidoc[]
 
 include::detections-req.asciidoc[leveloffset=+1]
 
+include::detections-logsdb-impact.asciidoc[leveloffset=+1]
+
 include::about-rules.asciidoc[]
 
 

docs/detections/detections-logsdb-impact.asciidoc

@@ -0,0 +1,65 @@
+[[detections-logsdb-index-mode-impact]]
+= Using logsdb index mode with {elastic-sec}
+
+NOTE: To use the {ref}/mapping-source-field.html#synthetic-source[synthetic `_source`] feature, you must have the appropriate subscription. Refer to the subscription page for https://www.elastic.co/subscriptions/cloud[Elastic Cloud] and {subscriptions}[Elastic Stack/self-managed] for the breakdown of available features and their associated subscription tiers.
+
+This topic explains the impact of using logsdb index mode with {elastic-sec}.
+
+With logsdb index mode, the original `_source` field is not stored in the index but can be reconstructed using {ref}/mapping-source-field.html#synthetic-source[synthetic `_source`].
+
+When the `_source` is reconstructed, {ref}/mapping-source-field.html#synthetic-source-modifications[modifications] are possible. Therefore, there could be a mismatch between users' expectations and how fields are formatted.
+
+Continue reading to find out how this affects specific {elastic-sec} components. 
+
+[discrete]
+[[logsdb-alerts]]
+== Alerts
+
+When alerts are generated, the `_source` event is copied into the alert to retain the original data. When the logsdb index mode is applied, the `_source` event stored in the alert is reconstructed using synthetic `_source`.
+
+If you're switching to use logsdb index mode, the `_source` field stored in the alert might look different in certain situations:
+
+* {ref}/mapping-source-field.html#synthetic-source-modifications-leaf-arrays[Arrays can be reconstructed differently or deduplicated]
+* {ref}/mapping-source-field.html#synthetic-source-modifications-field-names[Field names] 
+* `geo_point` data fields (refer to {ref}/mapping-source-field.html#synthetic-source-modifications-ranges[Representation of ranges] and {ref}/mapping-source-field.html#synthetic-source-precision-loss-for-point-types[Reduced precision of `geo_point` values] for more information)
+
+Alerts generated by the following rule types could be affected:
+
+* Custom query
+* Event correlation (non-sequence only)
+* Non-aggregate rule types (for example, {esql} rules that use non-aggregating queries)
+
+Alerts that are generated by threshold, {ml}, and event correlation sequence rules are not affected since they do not contain copies of the original source.
+
+[discrete]
+[[logsdb-rule-actions]]
+== Rule actions
+
+While we do not recommend using `_source` for actions, in cases where the action relies on the `_source`, the same limitations and changes apply.
+
+If you send alert notifications by enabling {kibana-ref}/alerting-getting-started.html#alerting-concepts-actions[actions] to the external systems that have workflows or automations based on fields formatted from the original source, they may be affected. In particular, this can happen when the fields used are arrays of objects.
+
+We recommend checking and adjusting the rule actions using `_source` before switching to logsdb index mode.
+
+[discrete]
+[[logsdb-runtime-fields]]
+== Runtime fields
+
+Runtime fields that reference `_source` may be affected. Some runtime fields might not work and need to be adjusted. For example, if an event was indexed with the value of `agent.name` in the dot-notation form, it will be returned in the nested form and might not work. 
+
+The following is an example of accessing `_source` that works with the logsdb index mode enabled:
+
+[source,console]
+----
+"source": """  emit(params._source.agent.name + "_____" + doc['agent.name'].value ); """ 
+"source": """  emit(params._source['agent']['name'] + "_____" + doc['agent.name'].value );  """
+"source": """  emit(field('agent.name').get(null) + "_____" + doc['agent.name'].value ); """
+"source": """  emit($('agent.name', null) + "_____" + doc['agent.name'].value ); """
+----
+
+The following will not work with synthetic source (logsdb index mode enabled):
+
+[source,console]
+----
+"source": """  emit(params._source['agent.name'] + "_____" + doc['agent.name'].value );  """
+----