OpenSearch/docs/reference/eql/eql.asciidoc

[role="xpack"]
[testenv="basic"]
[[eql]]
= EQL search
++++
<titleabbrev>EQL</titleabbrev>
++++

experimental::[]

{eql-ref}/index.html[Event Query Language (EQL)] is a query language used for
event-based, time-series data, such as logs.

[discrete]
[[eql-advantages]]
== Advantages of EQL

* *EQL lets you express relationships between events.* +
Many query languages allow you to match only single events. EQL lets you match a
sequence of events across different event categories and time spans.

* *EQL has a low learning curve.* +
EQL syntax looks like other query languages. It lets you write and read queries
intuitively, which makes for quick, iterative searching.

* *We designed EQL for security use cases.* +
While you can use EQL for any event-based data, we created EQL for threat
hunting. EQL not only supports indicator of compromise (IOC) searching but
makes it easy to describe activity that goes beyond IOCs.

[discrete]
[[eql-required-fields]]
== Required fields

EQL assumes each document in a data stream or index corresponds to an event. To
search using EQL, each document in the searched data stream or index must
include a _timestamp_ field and an _event category_ field.

{es} EQL uses the `@timestamp` and `event.category` fields from the
{ecs-ref}[Elastic Common Schema (ECS)] as the default timestamp and event
category fields. If your searched documents use a different timestamp or event
category field, you must specify it in the search request. See
<<specify-a-timestamp-or-event-category-field>>.

[discrete]
[[run-an-eql-search]]
== Run an EQL search

You can use the <<eql-search-api,EQL search API>> to run an EQL search.

The following request searches `my-index-000001` for events with an
`event.category` of `process` and a `process.name` of `cmd.exe`. Each document
in `my-index-000001` includes a `@timestamp` and `event.category` field.

[source,console]
----
GET /my-index-000001/_eql/search
{
  "query": """
    process where process.name == "cmd.exe"
  """
}
----
// TEST[setup:sec_logs]
// TEST[s/search/search\?filter_path\=\-\*\.events\.\*fields/]

The API returns the following response. Matching events are included in the
`hits.events` property. These events are sorted by timestamp, converted to
milliseconds since the https://en.wikipedia.org/wiki/Unix_time[Unix epoch], in
ascending order.

[source,console-result]
----
{
  "is_partial": false,
  "is_running": false,
  "took": 60,
  "timed_out": false,
  "hits": {
    "total": {
      "value": 2,
      "relation": "eq"
    },
    "events": [
       {
        "_index": "my-index-000001",
        "_type": "_doc",
        "_id": "OQmfCaduce8zoHT93o4H",
        "_score": null,
        "_source": {
          "@timestamp": "2020-12-06T11:04:05.000Z",
          "event": {
            "category": "process",
            "id": "edwCRnyD",
            "sequence": 1
          },
          "process": {
            "name": "cmd.exe",
            "executable": "C:\\Windows\\System32\\cmd.exe",
            "pid": 2012
          }
        }
      },
      {
        "_index": "my-index-000001",
        "_type": "_doc",
        "_id": "xLkCaj4EujzdNSxfYLbO",
        "_score": null,
        "_source": {
          "@timestamp": "2020-12-07T11:06:07.000Z",
          "event": {
            "category": "process",
            "id": "cMyt5SZ2",
            "sequence": 3
          },
          "process": {
            "name": "cmd.exe",
            "executable": "C:\\Windows\\System32\\cmd.exe",
            "pid": 2012
          }
        }
      }
    ]
  }
}
----
// TESTRESPONSE[s/"took": 60/"took": $body.took/]
// TESTRESPONSE[s/"_id": "OQmfCaduce8zoHT93o4H"/"_id": $body.hits.events.0._id/]
// TESTRESPONSE[s/"_id": "xLkCaj4EujzdNSxfYLbO"/"_id": $body.hits.events.1._id/]

[discrete]
[[eql-search-sequence]]
=== Search for a sequence of events

You can use EQL's <<eql-sequences,sequence syntax>> to search for an ordered
series of events.

The following EQL search request matches a sequence that:

. Starts with an event with:
+
--
* An `event.category` of `file`
* A `file.name` of `cmd.exe`
--
. Followed by an event with:
+
--
* An `event.category` of `process`
* A `process.name` that contains the substring `regsvr32`
--

[source,console]
----
GET /my-index-000001/_eql/search
{
  "query": """
    sequence
      [ file where file.name == "cmd.exe" ]
      [ process where stringContains(process.name, "regsvr32") ]
  """
}
----
// TEST[setup:sec_logs]

The API returns the following response. Matching sequences are included in the
`hits.sequences` property.

[source,console-result]
----
{
  "is_partial": false,
  "is_running": false,
  "took": 60,
  "timed_out": false,
  "hits": {
    "total": {
      "value": 1,
      "relation": "eq"
    },
    "sequences": [
      {
        "events": [
          {
            "_index": "my-index-000001",
            "_type": "_doc",
            "_id": "AtOJ4UjUBAAx3XR5kcCM",
            "_version" : 1,
            "_seq_no" : 3,
            "_primary_term" : 1,
            "_score": null,
            "_source": {
              "@timestamp": "2020-12-07T11:07:08.000Z",
              "event": {
                "category": "file",
                "id": "bYA7gPay",
                "sequence": 4
              },
              "file": {
                "accessed": "2020-12-07T11:07:08.000Z",
                "name": "cmd.exe",
                "path": "C:\\Windows\\System32\\cmd.exe",
                "type": "file",
                "size": 16384
              },
              "process": {
                "name": "cmd.exe",
                "executable": "C:\\Windows\\System32\\cmd.exe",
                "pid": 2012
              }
            }
          },
          {
            "_index": "my-index-000001",
            "_type": "_doc",
            "_id": "yDwnGIJouOYGBzP0ZE9n",
            "_version" : 1,
            "_seq_no" : 4,
            "_primary_term" : 1,
            "_score": null,
            "_source": {
              "@timestamp": "2020-12-07T11:07:09.000Z",
              "event": {
                "category": "process",
                "id": "aR3NWVOs",
                "sequence": 5
              },
              "process": {
                "name": "regsvr32.exe",
                "executable": "C:\\Windows\\System32\\regsvr32.exe",
                "pid": 2012
              }
            }
          }
        ]
      }
    ]
  }
}
----
// TESTRESPONSE[s/"took": 60/"took": $body.took/]
// TESTRESPONSE[s/"_id": "AtOJ4UjUBAAx3XR5kcCM"/"_id": $body.hits.sequences.0.events.0._id/]
// TESTRESPONSE[s/"_id": "yDwnGIJouOYGBzP0ZE9n"/"_id": $body.hits.sequences.0.events.1._id/]

You can use the <<eql-with-maxspan-keywords,`with maxspan` keywords>> to
constrain a sequence to a specified timespan.

The following EQL search request adds `with maxspan=1h` to the previous query.
This ensures all events in a matching sequence occur within `1h` (one hour) of
the first event's timestamp.

[source,console]
----
GET /my-index-000001/_eql/search
{
  "query": """
    sequence with maxspan=1h
      [ file where file.name == "cmd.exe" ]
      [ process where stringContains(process.name, "regsvr32") ]
  """
}
----
// TEST[setup:sec_logs]

You can further constrain matching event sequences using the
<<eql-by-keyword,`by` keyword>>.

The following EQL search request adds `by process.pid` to each event item. This
ensures events matching the sequence share the same `process.pid` field value.

[source,console]
----
GET /my-index-000001/_eql/search
{
  "query": """
    sequence with maxspan=1h
      [ file where file.name == "cmd.exe" ] by process.pid
      [ process where stringContains(process.name, "regsvr32") ] by process.pid
  """
}
----
// TEST[setup:sec_logs]

Because the `process.pid` field is shared across all events in the sequence, it
can be included using `sequence by`. The following query is equivalent to the
previous one.

[source,console]
----
GET /my-index-000001/_eql/search
{
  "query": """
    sequence by process.pid with maxspan=1h
      [ file where file.name == "cmd.exe" ]
      [ process where stringContains(process.name, "regsvr32") ]
  """
}
----
// TEST[setup:sec_logs]

The API returns the following response. The `hits.sequences.join_keys` property
contains the shared `process.pid` value for each matching event.

[source,console-result]
----
{
  "is_partial": false,
  "is_running": false,
  "took": 60,
  "timed_out": false,
  "hits": {
    "total": {
      "value": 1,
      "relation": "eq"
    },
    "sequences": [
      {
        "join_keys": [
          "2012"
        ],
        "events": [
          {
            "_index": "my-index-000001",
            "_type": "_doc",
            "_id": "AtOJ4UjUBAAx3XR5kcCM",
            "_version": 1,
            "_seq_no": 3,
            "_primary_term": 1,
            "_score": null,
            "_source": {
              "@timestamp": "2020-12-07T11:07:08.000Z",
              "event": {
                "category": "file",
                "id": "bYA7gPay",
                "sequence": 4
              },
              "file": {
                "accessed": "2020-12-07T11:07:08.000Z",
                "name": "cmd.exe",
                "path": "C:\\Windows\\System32\\cmd.exe",
                "type": "file",
                "size": 16384
              },
              "process": {
                "name": "cmd.exe",
                "executable": "C:\\Windows\\System32\\cmd.exe",
                "pid": 2012
              }
            }
          },
          {
            "_index": "my-index-000001",
            "_type": "_doc",
            "_id": "yDwnGIJouOYGBzP0ZE9n",
            "_version": 1,
            "_seq_no": 4,
            "_primary_term": 1,
            "_score": null,
            "_source": {
              "@timestamp": "2020-12-07T11:07:09.000Z",
              "event": {
                "category": "process",
                "id": "aR3NWVOs",
                "sequence": 5
              },
              "process": {
                "name": "regsvr32.exe",
                "executable": "C:\\Windows\\System32\\regsvr32.exe",
                "pid": 2012
              }
            }
          }
        ]
      }
    ]
  }
}
----
// TESTRESPONSE[s/"took": 60/"took": $body.took/]
// TESTRESPONSE[s/"_id": "AtOJ4UjUBAAx3XR5kcCM"/"_id": $body.hits.sequences.0.events.0._id/]
// TESTRESPONSE[s/"_id": "yDwnGIJouOYGBzP0ZE9n"/"_id": $body.hits.sequences.0.events.1._id/]

You can use the <<eql-until-keyword,`until` keyword>> to specify an expiration
event for sequences. Matching sequences must end before this event.

The following request adds `until [ process where event.type == "termination" ]`
to the previous query. This ensures matching sequences end before a `process`
event with an `event.type` of `termination`.

[source,console]
----
GET /my-index-000001/_eql/search
{
  "query": """
    sequence by process.pid with maxspan=1h
      [ file where file.name == "cmd.exe" ]
      [ process where stringContains(process.name, "regsvr32") ]
    until [ process where event.type == "termination" ]
  """
}
----
// TEST[setup:sec_logs]

[discrete]
[[specify-a-timestamp-or-event-category-field]]
=== Specify a timestamp or event category field

By default, the EQL search API uses `@timestamp` and `event.category` as the
required timestamp and event category fields. If your searched documents use
a different timestamp or event category field, you must specify it in the search
request using the `timestamp_field` or `event_category_field` parameters.

The event category field is typically mapped as a <<keyword,`keyword`>> or
<<constant-keyword,constant keyword>> field. The timestamp field is typically
mapped as a <<date,`date`>> or <<date_nanos,`date_nanos`>> field.

NOTE: You cannot use a <<nested,`nested`>> field or the sub-fields of a `nested`
field as the timestamp or event category field. See <<eql-nested-fields>>.

The following request uses the `timestamp_field` parameter to specify
`file.accessed` as the timestamp field. The request also uses the
`event_category_field` parameter to specify `file.type` as the event category
field.

[source,console]
----
GET /my-index-000001/_eql/search
{
  "timestamp_field": "file.accessed",
  "event_category_field": "file.type",
  "query": """
    file where (file.size > 1 and file.type == "file")
  """
}
----
// TEST[setup:sec_logs]

[discrete]
[[eql-search-filter-query-dsl]]
=== Filter using query DSL

You can use the `filter` parameter to specify an additional query using
<<query-dsl,query DSL>>. This query filters the documents on which the EQL query
runs.

The following request uses a `range` query to filter `my-index-000001` to only
documents with a `file.size` value greater than `1` but less than `1000000`
bytes. The EQL query in `query` parameter then runs on these filtered documents.

[source,console]
----
GET /my-index-000001/_eql/search
{
  "filter": {
    "range" : {
      "file.size" : {
        "gte" : 1,
        "lte" : 1000000
      }
    }
  },
  "query": """
    file where (file.type == "file" and file.name == "cmd.exe")
  """
}
----
// TEST[setup:sec_logs]

[discrete]
[[eql-search-case-sensitive]]
=== Run a case-sensitive EQL search

By default, matching for EQL queries is case-insensitive. You can use the
`case_sensitive` parameter to toggle case sensitivity on or off.

The following search request contains a query that matches `process` events
with a `process.executable` containing `System32`.

Because `case_sensitive` is `true`, this query only matches `process.executable`
values containing `System32` with the exact same capitalization. A
`process.executable` value containing `system32` or `SYSTEM32` would not match
this query.

[source,console]
----
GET /my-index-000001/_eql/search
{
  "keep_on_completion": true,
  "case_sensitive": true,
  "query": """
    process where stringContains(process.executable, "System32")
  """
}
----
// TEST[setup:sec_logs]

[discrete]
[[eql-search-async]]
=== Run an async EQL search

EQL searches are designed to run on large volumes of data quickly, often
returning results in milliseconds. For this reason, EQL searches are
_synchronous_ by default. The search request waits for complete results before
returning a response. 

However, complete results can take longer for searches across:

* <<frozen-indices,Frozen indices>>
* <<modules-cross-cluster-search,Multiple clusters>>
* Many shards

To avoid long waits, you can use the `wait_for_completion_timeout` parameter to
run an _asynchronous_, or _async_, EQL search.

Set `wait_for_completion_timeout` to a duration you'd like to wait
for complete search results. If the search request does not finish within this
period, the search becomes async and returns a response that includes:

* A search ID, which can be used to monitor the progress of the async search.
* An `is_partial` value of `true`, meaning the response does not contain
  complete search results.
* An `is_running` value of `true`, meaning the search is async and ongoing.

The async search continues to run in the background without blocking
other requests.

The following request searches the `frozen-my-index-000001` index, which has been
<<frozen-indices,frozen>> for storage and is rarely searched.

Because searches on frozen indices are expected to take longer to complete, the
request contains a `wait_for_completion_timeout` parameter value of `2s` (two
seconds). If the request does not return complete results in two seconds, the
search becomes async and returns a search ID.

[source,console]
----
GET /frozen-my-index-000001/_eql/search
{
  "wait_for_completion_timeout": "2s",
  "query": """
    process where process.name == "cmd.exe"
  """
}
----
// TEST[setup:sec_logs]
// TEST[s/frozen-my-index-000001/my-index-000001/]

After two seconds, the request returns the following response. Note `is_partial`
and `is_running` properties are `true`, indicating an async search.

[source,console-result]
----
{
  "id": "FmNJRUZ1YWZCU3dHY1BIOUhaenVSRkEaaXFlZ3h4c1RTWFNocDdnY2FSaERnUTozNDE=",
  "is_partial": true,
  "is_running": true,
  "took": 2000,
  "timed_out": false,
  "hits": ...
}
----
// TESTRESPONSE[s/FmNJRUZ1YWZCU3dHY1BIOUhaenVSRkEaaXFlZ3h4c1RTWFNocDdnY2FSaERnUTozNDE=/$body.id/]
// TESTRESPONSE[s/"is_partial": true/"is_partial": $body.is_partial/]
// TESTRESPONSE[s/"is_running": true/"is_running": $body.is_running/]
// TESTRESPONSE[s/"took": 2000/"took": $body.took/]
// TESTRESPONSE[s/"hits": \.\.\./"hits": $body.hits/]

You can use the the search ID and the <<get-async-eql-search-api,get async EQL
search API>> to check the progress of an async search.

The get async EQL search API also accepts a `wait_for_completion_timeout`
parameter. If ongoing search does not complete during this period, the response
returns an `is_partial` value of `true` and no search results.

The following get async EQL search API request checks the progress of the
previous async EQL search. The request specifies a `wait_for_completion_timeout`
query parameter value of `2s` (two seconds).

[source,console]
----
GET /_eql/search/FmNJRUZ1YWZCU3dHY1BIOUhaenVSRkEaaXFlZ3h4c1RTWFNocDdnY2FSaERnUTozNDE=?wait_for_completion_timeout=2s
----
// TEST[skip: no access to search ID]

The request returns the following response. Note `is_partial` and `is_running`
are `false`, indicating the async search has finished and the search results
in the `hits` property are complete.

[source,console-result]
----
{
  "id": "FmNJRUZ1YWZCU3dHY1BIOUhaenVSRkEaaXFlZ3h4c1RTWFNocDdnY2FSaERnUTozNDE=",
  "is_partial": false,
  "is_running": false,
  "took": 2000,
  "timed_out": false,
  "hits": ...
}
----
// TESTRESPONSE[s/FmNJRUZ1YWZCU3dHY1BIOUhaenVSRkEaaXFlZ3h4c1RTWFNocDdnY2FSaERnUTozNDE=/$body.id/]
// TESTRESPONSE[s/"took": 2000/"took": $body.took/]
// TESTRESPONSE[s/"hits": \.\.\./"hits": $body.hits/]

[discrete]
[[eql-search-store-async-eql-search]]
=== Change the search retention period

By default, the EQL search API stores async searches for five days. After this
period, any searches and their results are deleted. You can use the `keep_alive`
parameter to change this retention period.

In the following EQL search request, the `keep_alive` parameter is `2d` (two
days). If the search becomes async, its results
are stored on the cluster for two days. After two days, the async
search and its results are deleted, even if it's still ongoing.

[source,console]
----
GET /my-index-000001/_eql/search
{
  "keep_alive": "2d",
  "wait_for_completion_timeout": "2s",
  "query": """
    process where process.name == "cmd.exe"
  """
}
----
// TEST[setup:sec_logs]

You can use the <<get-async-eql-search-api,get async EQL search API>>'s
`keep_alive`parameter to later change the retention period. The new
retention period starts after the get request executes.

The following request sets the `keep_alive` query parameter to `5d` (five days).
The async search and its results are deleted five days after the get request
executes.

[source,console]
----
GET /_eql/search/FmNJRUZ1YWZCU3dHY1BIOUhaenVSRkEaaXFlZ3h4c1RTWFNocDdnY2FSaERnUTozNDE=?keep_alive=5d
----
// TEST[skip: no access to search ID]

You can use the <<delete-async-eql-search-api,delete async EQL search API>> to
manually delete an async EQL search before the `keep_alive` period ends. If the
search is still ongoing, this cancels the search request.

The following request deletes an async EQL search and its results.

[source,console]
----
DELETE /_eql/search/FmNJRUZ1YWZCU3dHY1BIOUhaenVSRkEaaXFlZ3h4c1RTWFNocDdnY2FSaERnUTozNDE=?keep_alive=5d
----
// TEST[skip: no access to search ID]

[discrete]
[[eql-search-store-sync-eql-search]]
=== Store synchronous EQL searches

By default, the EQL search API only stores async searches that cannot be
completed within the period set by `wait_for_completion_timeout`.

To save the results of searches that complete during this period, set the
`keep_on_completion` parameter to `true`.

In the following search request, `keep_on_completion` is `true`. This means the
search results are stored on the cluster, even if the search completes within
the `2s` (two-second) period set by the `wait_for_completion_timeout` parameter.

[source,console]
----
GET /my-index-000001/_eql/search
{
  "keep_on_completion": true,
  "wait_for_completion_timeout": "2s",
  "query": """
    process where process.name == "cmd.exe"
  """
}
----
// TEST[setup:sec_logs]

The API returns the following response. A search ID is provided in the `id`
property. `is_partial` and `is_running` are `false`, indicating the EQL search
was synchronous and returned complete results in `hits`.

[source,console-result]
----
{
  "id": "FjlmbndxNmJjU0RPdExBTGg0elNOOEEaQk9xSjJBQzBRMldZa1VVQ2pPa01YUToxMDY=",
  "is_partial": false,
  "is_running": false,
  "took": 52,
  "timed_out": false,
  "hits": ...
}
----
// TESTRESPONSE[s/FjlmbndxNmJjU0RPdExBTGg0elNOOEEaQk9xSjJBQzBRMldZa1VVQ2pPa01YUToxMDY=/$body.id/]
// TESTRESPONSE[s/"took": 52/"took": $body.took/]
// TESTRESPONSE[s/"hits": \.\.\./"hits": $body.hits/]

You can use the search ID and the <<get-async-eql-search-api,get async EQL
search API>> to retrieve the same results later.

[source,console]
----
GET /_eql/search/FjlmbndxNmJjU0RPdExBTGg0elNOOEEaQk9xSjJBQzBRMldZa1VVQ2pPa01YUToxMDY=
----
// TEST[skip: no access to search ID]

Saved synchronous searches are still subject to the retention period set by the
`keep_alive` parameter. After this period, the search and its results are
deleted.

You can also manually delete saved synchronous searches using the
<<delete-async-eql-search-api,delete async EQL search API>>.

include::syntax.asciidoc[]
include::functions.asciidoc[]
include::pipes.asciidoc[]