## Summary
Adds a workaround for EQL bug: https://github.com/elastic/elasticsearch/issues/77152
Adds the safety feature mentioned here: https://github.com/elastic/kibana/issues/110802
Adds the ability to ignore particular [fields](https://www.elastic.co/guide/en/elasticsearch/reference/current/search-fields.html#search-fields-param) when the field is merged with [_source](https://www.elastic.co/guide/en/elasticsearch/reference/current/search-fields.html#source-filtering). Also fixes an EQL bug where EQL is introducing the meta field of `_ignored` within the fields and causing documents to not be indexable when we merge with the fields from EQL.
Alerting document creation uses the fields API to get [runtime field](https://www.elastic.co/guide/en/elasticsearch/reference/current/runtime.html), [constant keyword](https://www.elastic.co/guide/en/elasticsearch/reference/master/keyword.html#constant-keyword-field-type), etc... that are only available within the [fields API](https://www.elastic.co/guide/en/elasticsearch/reference/current/search-fields.html#search-fields-param) and then merges the field values not found within the `_source` document with the `_source` document and then finally indexes this merged document as an alert document.
This fix/ability is a "safety feature" in that if a problematic [runtime field](https://www.elastic.co/guide/en/elasticsearch/reference/current/runtime.html), [constant keyword](https://www.elastic.co/guide/en/elasticsearch/reference/master/keyword.html#constant-keyword-field-type) is discovered or another bug along the stack we can set a `kibana.yml` key/value pair to ignore the problematic field.
This _WILL NOT_ remove problematic fields from the `_source` document. This will only ignore problematic constant keyword, runtime fields, aliases, or anything else found in the fields API that is causing merge issues.
This PR:
* Adds a `alertIgnoreFields` `kibana.yml` array key with a default of an empty array if not specified.
* Plumbs the `alertIgnoreFields` through the stack and into the fields/_source merge strategies of `missingFields` and `allFields`
* Adds a temporary `isEqlBug77152` where it hard codes an ignore of `_ignored` until the EQL problem is fixed and then we will remove the workaround
* Adds unit tests
* Adds e2e tests which covers the described use cases above.
The `alertIgnoreFields` key/value within `kibana.yml` if set should be an array of strings of each field you want to ignore. This can also contain regular expressions as long as they are of the form, `"/regex/"` in the array.
Example if you want to ignore fields that are problematic called "host.name" and then one in which you want to ignore all fields that start with "user." using a regular expression:
```yml
xpack.securitySolution.alertIgnoreFields: ['host.name', '/user\..*/']
```
Although there are e2e tests which exercise the use cases...
If you want to manual test the EQL bug fix you would add these documents in dev tools:
```json
# Delete and add a mapping with a small ignore_above.
DELETE eql-issue-ignore-fields-delme
PUT eql-issue-ignore-fields-delme
{
"mappings" : {
"dynamic": "strict",
"properties" : {
"@timestamp": {
"type": "date"
},
"some_keyword" : {
"ignore_above": 5,
"type" : "keyword"
},
"other_keyword" : {
"ignore_above": 10,
"type" : "keyword"
}
}
}
}
# Add a single document with one field that will be truncated and a second that will not.
PUT eql-issue-ignore-fields-delme/_doc/1
{
"@timestamp": "2021-09-02T04:13:05.626Z",
"some_keyword": "longer than normal",
"other_keyword": "normal"
}
```
Then create an alert which queries everything from it:
<img width="1155" alt="Screen Shot 2021-09-01 at 10 15 06 PM" src="https://user-images.githubusercontent.com/1151048/131781042-faa424cf-65a5-4ebb-b801-3f188940c81d.png">
and ensure signals are created:
<img width="2214" alt="Screen Shot 2021-09-01 at 10 30 18 PM" src="https://user-images.githubusercontent.com/1151048/131782069-b9ab959c-f22d-44d5-baf0-561fe349c037.png">
To test the manual exclusions of any other problematic fields, create any index which has runtime fields or `constant keywords` but does not have anything within the `_source` document using dev tools. For example you can use `constant keyword` like so
```json
PUT constant-keywords-deleme
{
"mappings": {
"dynamic": "strict",
"properties": {
"@timestamp": {
"type": "date"
},
"testing_ignored": {
"properties": {
"constant": {
"type": "constant_keyword",
"value": "constant_value"
}
}
},
"testing_regex": {
"type": "constant_keyword",
"value": "constant_value"
},
"normal_constant": {
"type": "constant_keyword",
"value": "constant_value"
},
"small_field": {
"type": "keyword",
"ignore_above": 10
}
}
}
}
PUT constant-keywords-deleme/_doc/1
{
"@timestamp": "2021-09-02T04:20:01.760Z"
}
```
Set in your `kibana.yml` the key/value of:
```yml
xpack.securitySolution.alertIgnoreFields: ['testing_ignored.constant', '/.*_regex/']
```
Setup a rule to run:
<img width="1083" alt="Screen Shot 2021-09-01 at 10 23 23 PM" src="https://user-images.githubusercontent.com/1151048/131781696-fea0d421-836f-465c-9be6-5289fbb622a4.png">
Once it runs you should notice that the constant values for testing are not on the signals table since it only typically exists in the fields API:
<img width="1166" alt="Screen Shot 2021-09-01 at 10 26 16 PM" src="https://user-images.githubusercontent.com/1151048/131781782-1684fb1d-bed9-4cf0-be9a-0abe1f0f34d1.png">
But the normal one still exists:
<img width="1136" alt="Screen Shot 2021-09-01 at 10 26 31 PM" src="https://user-images.githubusercontent.com/1151048/131781827-5450c693-de9e-4285-b082-9f7a2cbd5d07.png">
If you change the `xpack.securitySolution.alertIgnoreFields` by removing it and re-generate the signals you will see these values added back.
### Checklist
Delete any items that are not applicable to this PR.
- [x] [Unit or functional tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html) were updated or added to match the most common scenarios
- [x] If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the [docker list](https://github.com/elastic/kibana/blob/master/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
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