Monitoring audit logs in Amazon OpenSearch Service

If your Amazon OpenSearch Service domain uses fine-grained access control, you can enable audit logs for your data. Audit logs are highly customizable and let you track user activity on your OpenSearch clusters, including authentication success and failures, requests to OpenSearch, index changes, and incoming search queries. The default configuration tracks a popular set of user actions, but we recommend tailoring the settings to your exact needs.

Just like OpenSearch application logs and slow logs, OpenSearch Service publishes audit logs to CloudWatch Logs. If enabled, standard CloudWatch pricing applies.

Note

To enable audit logs, your user role must be mapped to the security_manager role, which gives you access to the OpenSearch plugins/_security REST API. To learn more, see Modifying the master user.

Limitations

Audit logs have the following limitations:

• Audit logs don't include cross-cluster search requests that were rejected by the destination's domain access policy.

• The maximum size of each audit log message is 10,000 characters. The audit log message is truncated if it exceeds this limit.

Enabling audit logs

Enabling audit logs is a two-step process. First, you configure your domain to publish audit logs to CloudWatch Logs. Then, you enable audit logs in OpenSearch Dashboards and configure them to meet your needs.

Important

If you encounter an error while following these steps, see Can't enable audit logs for troubleshooting information.

Step 1: Enable audit logs and configure an access policy

These steps describe how to enable audit logs using the console. You can also enable them using the AWS CLI, or the OpenSearch Service API.

To enable audit logs for an OpenSearch Service domain (console)

1. Choose the domain to open its configuration, then go to the Logs tab.

2. Select Audit logs and then Enable.

3. Create a CloudWatch log group, or choose an existing one.

4. Choose an access policy that contains the appropriate permissions, or create a policy using the JSON that the console provides:

   {
     "Version": "2012-10-17",
     "Statement": [
       {
         "Effect": "Allow",
         "Principal": {
           "Service": "es.amazonaws.com"
         },
         "Action": [
           "logs:PutLogEvents",
           "logs:CreateLogStream"
         ],
         "Resource": "cw_log_group_arn"
       }
     ]
   }

   We recommend that you add the aws:SourceAccount and aws:SourceArn condition keys to the policy to protect yourself against the confused deputy problem. The source account is the owner of the domain and the source ARN is the ARN of the domain. Your domain must be on service software R20211203 or later in order to add these condition keys.

   For example, you could add the following condition block to the policy:

   "Condition": {
       "StringEquals": {
           "aws:SourceAccount": "account-id"
       },
       "ArnLike": {
           "aws:SourceArn": "arn:aws:es:region:account-id:domain/domain-name"
       }
   }

5. Choose Enable.

Step 2: Turn on audit logs in OpenSearch Dashboards

After you enable audit logs in the OpenSearch Service console, you must also enable them in OpenSearch Dashboards and configure them to match your needs.

1. Open OpenSearch Dashboards and choose Security from the left side menu.

2. Choose Audit logs.

3. Choose Enable audit logging.

The Dashboards UI offers full control of audit log settings under General settings and Compliance settings. For a description of all configuration options, see Audit log settings.

Enable audit logging using the AWS CLI

The following AWS CLI command enables audit logs on an existing domain:

aws opensearch update-domain-config --domain-name my-domain --log-publishing-options "AUDIT_LOGS={CloudWatchLogsLogGroupArn=arn:aws:logs:us-east-1:123456789012:log-group:my-log-group,Enabled=true}"

You can also enable audit logs when you create a domain. For detailed information, see the AWS CLI Command Reference.

Enable audit logging using the configuration API

The following request to the configuration API enables audit logs on an existing domain:

POST https://es.us-east-1.amazonaws.com/2021-01-01/opensearch/domain/my-domain/config
{
  "LogPublishingOptions": {
    "AUDIT_LOGS": {
      "CloudWatchLogsLogGroupArn":"arn:aws:logs:us-east-1:123456789012:log-group1:sample-domain",
      "Enabled":true
    }
  }
}

For more information, see the Amazon OpenSearch Service API reference.

Audit log layers and categories

Cluster communication occurs over two separate layers: the REST layer and the transport layer.

• The REST layer covers communication with HTTP clients such as curl, Logstash, OpenSearch Dashboards, the Java high-level REST client, the Python Requests library—all HTTP requests that arrive at the cluster.

• The transport layer covers communication between nodes. For example, after a search request arrives at the cluster (over the REST layer), the coordinating node serving the request sends the query to other nodes, receives their responses, gathers the necessary documents, and collates them into the final response. Operations such as shard allocation and rebalancing also occur over the transport layer.

You can enable or disable audit logs for entire layers, as well as individual audit categories for a layer. The following table contains a summary of audit categories and the layers for which they are available.

Category	Description	Available for REST	Available for transport
FAILED_LOGIN	A request contained invalid credentials, and authentication failed.	Yes	Yes
MISSING_PRIVILEGES	A user did not have the privileges to make the request.	Yes	Yes
GRANTED_PRIVILEGES	A user had the privileges to make the request.	Yes	Yes
OPENSEARCH_SECURITY_INDEX_ATTEMPT	A request tried to modify the .opendistro_security index.	No	Yes
AUTHENTICATED	A request contained valid credentials, and authentication succeeded.	Yes	Yes
INDEX_EVENT	A request performed an administrative operation on an index, such as creating one, setting an alias, or performing a force merge. The full list of indices:admin/ actions that this category includes are available in the OpenSearch documentation.	No	Yes

In addition to these standard categories, fine-grained access control offers several additional categories designed to meet data compliance requirements.

Category	Description
COMPLIANCE_DOC_READ	A request performed a read event on a document in an index.
COMPLIANCE_DOC_WRITE	A request performed a write event on a document in an index.
COMPLIANCE_INTERNAL_CONFIG_READ	A request performed a read event on the .opendistro_security index.
COMPLIANCE_INTERNAL_CONFIG_WRITE	A request performed a write event on the .opendistro_security index.

You can have any combination of categories and message attributes. For example, if you send a REST request to index a document, you might see the following lines in the audit logs:

• AUTHENTICATED on REST layer (authentication)

• GRANTED_PRIVILEGE on transport layer (authorization)

• COMPLIANCE_DOC_WRITE (document written to an index)

Audit log settings

Audit logs have numerous configuration options.

General settings

General settings let you enable or disable individual categories or entire layers. We highly recommend leaving GRANTED_PRIVILEGES and AUTHENTICATED as excluded categories. Otherwise, these categories are logged for every valid request to the cluster.

Name	Backend setting	Description
REST layer	enable_rest	Enable or disable events that occur on the REST layer.
REST disabled categories	disabled_rest_categories	Specify audit categories to ignore on the REST layer. Modifying these categories can dramatically increase the size of the audit logs.
Transport layer	enable_transport	Enable or disable events that happen on the transport layer.
Transport disabled categories	disabled_transport_categories	Specify audit categories which must be ignored on the transport layer. Modifying these categories can dramatically increase the size of the audit logs.

Attribute settings let you customize the amount of detail in each log line.

Name	Backend setting	Description
Bulk requests	resolve_bulk_requests	Enabling this setting generates a log for each document in a bulk request, which can dramatically increase the size of the audit logs.
Request body	log_request_body	Include the request body of the requests.
Resolve indices	resolve_indices	Resolve aliases to indices.

Use ignore settings to exclude a set of users or API paths:

Name	Backend setting	Description
Ignored users	ignore_users	Specify users that you want to exclude.
Ignored requests	ignore_requests	Specify request patterns that you want to exclude.

Compliance settings

Compliance settings let you tune for index, document, or field-level access.

Name	Backend setting	Description
Compliance logging	enable_compliance	Enable or disable compliance logging.

You can specify the following settings for read and write event logging.

Name	Backend setting	Description
Internal config logging	internal_config	Enable or disable logging of events on the .opendistro_security index.

You can specify the following settings for read events.

Name	Backend setting	Description
Read metadata	read_metadata_only	Include only metadata for read events. Do not include any document fields.
Ignored users	read_ignore_users	Do not include certain users for read events.
Watched fields	read_watched_fields	Specify the indices and fields to watch for read events. Adding watched fields generates one log per document access, which can dramatically increase the size of the audit logs. Watched fields support index patterns and field patterns: { "index-name-pattern": [ "field-name-pattern" ], "logs*": [ "message" ], "twitter": [ "id", "user*" ] }

You can specify the following settings for write events.

Name	Backend setting	Description
Write metadata	write_metadata_only	Include only metadata for write events. Do not include any document fields.
Log diffs	write_log_diffs	If write_metadata_only is false, include only the differences between write events.
Ignored users	write_ignore_users	Do not include certain users for write events.
Watch indices	write_watched_indices	Specify the indices or index patters to watch for write events. Adding watched fields generates one log per document access, which can dramatically increase the size of the audit logs.

Audit log example

This section includes an example configuration, search request, and the resulting audit log for all read and write events of an index.

Step 1: Configure audit logs

After you enable the publishing of audit logs to a CloudWatch Logs group, navigate to the OpenSearch Dashboards audit logging page and choose Enable audit logging.

1. In General Settings, choose Configure and make sure that the REST layer is enabled.

2. In Compliance Settings, choose Configure.

3. Under Write, in Watched Fields, add accounts for all write events to this index.

4. Under Read, in Watched Fields, add ssn and id- fields of the accounts index:

   {
     "accounts-": [
       "ssn",
       "id-"
     ]
   }

Step 2: Perform read and write events

1. Navigate to OpenSearch Dashboards, choose Dev Tools, and index a sample document:

   PUT accounts/_doc/0
   {
     "ssn": "123",
     "id-": "456"
   }

2. To test a read event, send the following request:

   GET accounts/_search
   {
     "query": {
       "match_all": {}
     }
   }

Step 3: Observe the logs

1. Open the CloudWatch console at https://console.aws.amazon.com/cloudwatch/.

2. In the navigation pane, choose Log groups.

3. Choose the log group that you specified while enabling audit logs. Within the log group, OpenSearch Service creates a log stream for each node in your domain.

4. In Log streams, choose Search all.

5. For the read and write events, see the corresponding logs. You can expect a delay of 5 seconds before the log appears.

   Sample write audit log

   {
     "audit_compliance_operation": "CREATE",
     "audit_cluster_name": "824471164578:audit-test",
     "audit_node_name": "be217225a0b77c2bd76147d3ed3ff83c",
     "audit_category": "COMPLIANCE_DOC_WRITE",
     "audit_request_origin": "REST",
     "audit_compliance_doc_version": 1,
     "audit_node_id": "3xNJhm4XS_yTzEgDWcGRjA",
     "@timestamp": "2020-08-23T05:28:02.285+00:00",
     "audit_format_version": 4,
     "audit_request_remote_address": "3.236.145.227",
     "audit_trace_doc_id": "lxnJGXQBqZSlDB91r_uZ",
     "audit_request_effective_user": "admin",
     "audit_trace_shard_id": 8,
     "audit_trace_indices": [
       "accounts"
     ],
     "audit_trace_resolved_indices": [
       "accounts"
     ]
   }

   Sample read audit log

   {
     "audit_cluster_name": "824471164578:audit-docs",
     "audit_node_name": "806f6050cb45437e2401b07534a1452f",
     "audit_category": "COMPLIANCE_DOC_READ",
     "audit_request_origin": "REST",
     "audit_node_id": "saSevm9ASte0-pjAtYi2UA",
     "@timestamp": "2020-08-31T17:57:05.015+00:00",
     "audit_format_version": 4,
     "audit_request_remote_address": "54.240.197.228",
     "audit_trace_doc_id": "config:7.7.0",
     "audit_request_effective_user": "admin",
     "audit_trace_shard_id": 0,
     "audit_trace_indices": [
       "accounts"
     ],
     "audit_trace_resolved_indices": [
       "accounts"
     ]
   }

To include the request body, return to Compliance settings in OpenSearch Dashboards and disable Write metadata. To exclude events by a specific user, add the user to Ignored Users.

For a description of each audit log field, see Audit log field reference. For information on searching and analyzing your audit log data, see Analyzing Log Data with CloudWatch Logs Insights in the Amazon CloudWatch Logs User Guide.

Configuring audit logs using the REST API

We recommend using OpenSearch Dashboards to configure audit logs, but you can also use the fine-grained access control REST API. This section contains a sample request. Full documentation on the REST API is available in the OpenSearch documentation.

PUT _opendistro/_security/api/audit/config
{
  "enabled": true,
  "audit": {
    "enable_rest": true,
    "disabled_rest_categories": [
      "GRANTED_PRIVILEGES",
      "AUTHENTICATED"
    ],
    "enable_transport": true,
    "disabled_transport_categories": [
      "GRANTED_PRIVILEGES",
      "AUTHENTICATED"
    ],
    "resolve_bulk_requests": true,
    "log_request_body": true,
    "resolve_indices": true,
    "exclude_sensitive_headers": true,
    "ignore_users": [
      "kibanaserver"
    ],
    "ignore_requests": [
      "SearchRequest",
      "indices:data/read/*",
      "/_cluster/health"
    ]
  },
  "compliance": {
    "enabled": true,
    "internal_config": true,
    "external_config": false,
    "read_metadata_only": true,
    "read_watched_fields": {
      "read-index-1": [
        "field-1",
        "field-2"
      ],
      "read-index-2": [
        "field-3"
      ]
    },
    "read_ignore_users": [
      "read-ignore-1"
    ],
    "write_metadata_only": true,
    "write_log_diffs": false,
    "write_watched_indices": [
      "write-index-1",
      "write-index-2",
      "log-*",
      "*"
    ],
    "write_ignore_users": [
      "write-ignore-1"
    ]
  }
}