Elasticsearch (om_elasticsearch)
This module forwards logs to an Elasticsearch server. It will connect to the URL specified in the configuration in either plain HTTP or HTTPS mode. This module supports bulk data operations and dynamic indexing. Event data is sent in batches, reducing the latency caused by the HTTP responses, thus improving Elasticsearch server performance. HTTP protocol errors result in the entire batch being retried. For data errors reported by the Elasticsearch server, the server response is parsed and only the failed Event data is included in the retry. If the same batch (or partial batch) has not been accepted by the server after RetryLimit retries are exhausted, the batch will be dropped, or the module will stop (according to OnError).
| To examine the supported platforms, see the list of installation packages. |
| This module requires the xm_json extension module to be loaded to convert the payload to JSON. See the Output log format section for information on the format of the payload. |
Output log format
om_elasticsearch forwards log records over HTTP(S) as JSON payload.
The JSON format depends on the value of the $raw_event field.
The module checks if the value of $raw_event is valid JSON and applies the following rules:
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If it is valid JSON, the value is forwarded as is.
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If it is not valid JSON, the log record is converted to JSON in the following format:
{ "raw_event": "<json_escaped_raw_event>" }
Additional metadata, including the NXLog Agent-specific fields EventReceivedTime, SourceModuleName, and SourceModuleType, will not be included in the output unless these values have been written to the $raw_event field.
The processing required to achieve this depends on the format of the input data, but generally, it means you need to:
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Parse the log record according to the data format.
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If the input data is already in JSON format, use parse_json() to parse
$raw_eventinto fields. -
If the input is unstructured plain text data, copy the value of
$raw_eventto a custom field.
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Create and populate any additional custom fields.
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Use to_json() to convert the fields to JSON format and update the value of
$raw_event.
See the Examples section for NXLog Agent configuration examples of the above.
Date format in Elasticsearch
Date strings in the JSON output need to be in a format that is recognized by Elasticsearch for them to be saved as date fields. See the Elasticsearch documentation on the Date field type and format. NXLog Agent provides several ways to format datetime fields in the output and which one to use depends on how log records are being processed.
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By default, the xm_json module outputs datetime fields in a format that is compatible with Elasticsearch:
YYYY-MM-DDThh:mm:ss.sTZ. If you are using the to_json() procedure and need to output dates in a different format, specify the DateFormat module-level directive. -
If you are not using the xm_json module to convert data to JSON, you can make use of the DateFormat global directive or convert datetime fields individually with the strftime function.
For more information on how to handle date fields, see Log event timestamps in the NXLog Platform User Guide.
Configuration
The om_elasticsearch module accepts the following directives in addition to the common module directives.
Required directives
The following directive is required for the module to start.
This mandatory directive specifies the URL for the module to POST the event data.
If multiple URL directives are specified, the module works in a failover configuration.
If a destination becomes unavailable, the module automatically fails over to the next one.
If the last destination becomes unavailable, the module will fail over to the first destination.
The module operates in plain HTTP or HTTPS mode depending on the URL provided. If the port number is not explicitly indicated in the URL, it defaults to port 80 for HTTP and port 443 for HTTPS.
The URL should point to the _bulk endpoint, or Elasticsearch will return 400 Bad Request.
When sending logs to a data stream, the URL needs to contain the stream’s name, e.g.
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HTTPS directives
The following directives configure secure data transfer via HTTPS.
Set this directive to |
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Set this directive to |
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Set this directive to |
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Set this directive to the path of a directory containing Certificate Authority (CA) certificates.
The module uses these certificates to verify the certificate presented by the remote host.
Name the certificate files using the OpenSSL hashed format: the hash of the certificate followed by For example, if the certificate hash is To trust a remote host’s self-signed certificate, include a copy of it in this directory. If this directive isn’t specified, NXLog Agent falls back to the default operating system root certificate store.
Unix-like operating systems commonly store root certificates in In addition, Microsoft’s PKI repository contains root certificates for Microsoft services. This directive is mutually exclusive with the HTTPSCAThumbprint, HTTPSCAPattern, and HTTPSSearchAllCertStores directives. |
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Set this directive to the path of the Certificate Authority (CA) certificate used to verify the certificate presented by the remote host. To trust a remote host’s self-signed certificate, specify the remote host’s certificate itself. For certificates signed by an intermediate CA, the specified certificate must contain the complete certificate chain (certificate bundle). This directive is mutually exclusive with the HTTPSCAThumbprint, HTTPSCAPattern, and HTTPSSearchAllCertStores directives. |
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Set this directive to a PCRE2-compliant regular expression to locate a suitable Certificate Authority (CA) certificate. This directive is supported on Windows and macOS. On Windows, the certificate must be in the Windows Certificate Store. On macOS, the certificate must be in the system keychain. NXLog Agent matches the pattern against a string built from the certificate’s fields in this order: The pattern doesn’t need to match every field.
Include only the fields you want to match, and use For example, the following pattern matches only the This produces the following output in the NXLog Agent log file:
If the pattern matches multiple certificates, NXLog Agent uses the first match. If the certificate changes, restart NXLog Agent to apply the new certificate. This directive is mutually exclusive with the HTTPSCAThumbprint, HTTPSCADir, HTTPSCAFile, and HTTPSSearchAllCertStores directives.
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Set this directive to the thumbprint of the Certificate Authority (CA) certificate used to verify the certificate presented by the remote host. This directive is supported on Windows and macOS. On Windows, copy the hexadecimal fingerprint string from Windows Certificate Manager (certmgr.msc). The certificate must be in a Windows certificate store accessible by NXLog Agent. On macOS, obtain the hexadecimal fingerprint string from the Keychain Access application. The certificate must be accessible in the system keychain. Whitespaces and colons are automatically removed. This directive is mutually exclusive with the HTTPSCADir, HTTPSCAFile, HTTPSCAPattern, and HTTPSSearchAllCertStores directives.
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Set this directive to the path of the certificate file to present to the remote host during the HTTPS handshake. |
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Set this directive to the path of the private key file corresponding to the certificate specified by HTTPSCertFile. |
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Set this directive to a PCRE2-compliant pattern to identify the certificate and its corresponding private key. This directive is supported on Windows and macOS. NXLog Agent matches the pattern against a string built from the certificate’s fields in this order: The pattern doesn’t need to match every field.
Include only the fields you want to match, and use On Windows, import the certificate in PFX format into the On macOS, ensure the certificate and its private key are present in the System Keychain ( During configuration, NXLog Agent resolves this directive into the corresponding HTTPSCertThumbprint value. If the pattern matches multiple certificates, NXLog Agent uses the first match. This directive is not dynamic; restart NXLog Agent to apply a changed certificate. We recommend keeping the certificate storage referenced by this directive well-maintained for optimal performance. This directive is mutually exclusive with the HTTPSCertThumbprint, HTTPSCertFile and HTTPSCertKeyFile directives. Configuration examples: or This produces the following output in the NXLog Agent log file:
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Set this directive to the thumbprint of the certificate to present to the remote host during the HTTPS handshake. Whitespaces and colons are automatically removed. This directive is supported on Windows and macOS. On Windows, copy the hexadecimal fingerprint string from Windows Certificate Manager (certmgr.msc).
Import the certificate to the When the global directive UseCNGCertificates is set to
When UseCNGCertificates is set to On macOS, obtain the hexadecimal fingerprint string from the Keychain Access application.
The certificate and its associated private key must be present in the System Keychain ( For example:
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Set this directive to the path of a directory containing certificate revocation list (CRL) files.
The module uses these files to reject connections from hosts presenting a revoked certificate.
Name the files using the OpenSSL hashed format: the hash of the issuer followed by For example, if the hash is |
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Set this directive to the path of the certificate revocation list (CRL) file used to reject connections from hosts presenting a revoked certificate. To generate a CRL file using OpenSSL: |
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Set this directive to the path of a file containing Diffie-Hellman parameters for key exchange. Generate the parameters using dhparam(1ssl). If this directive is not set, the module uses default parameters. See the OpenSSL Wiki for further details. |
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Set this directive to the passphrase of the private key specified by HTTPSCertKeyFile. This directive applies only to encrypted private keys. To generate a private key with Triple DES encryption using OpenSSL: |
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Set this directive to This directive is only supported on Windows. |
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Set this directive to |
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Set this directive to |
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Set this directive to override the permitted cipher list for TLSv1.2 and below.
Use the format described in the ciphers(1ssl) man page.
For example, specify
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Set this directive to override the permitted cipher list for TLSv1.3. Use the same format as HTTPSSSLCipher. Refer to the OpenSSL documentation for a list of valid TLS v1.3 cipher suites. The default is:
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Set this directive to
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Set this directive to restrict the TLS/SSL protocols the module accepts.
Specify a comma-separated list of the following values: |
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Set this directive to This directive depends on the values of the HTTPSAllowUntrusted and HTTPSRequireCert directives:
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Set this directive to the signature algorithm parameter to pass to the Windows SSL library. Accepted values depend on the available encryption providers. This directive is only supported on Windows. |
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Set this directive to the hostname to use for Server Name Indication (SNI) in HTTPS mode. If not set, the module uses the hostname specified in the URL directive. |
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Set this directive to |
Optional directives
This optional directive specifies an additional header to be added to each HTTP request. |
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This boolean directive determines whether the event data is inserted into
a data stream. By default its value is |
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This directive allows to specify a custom
_id field
for Elasticsearch documents. If the directive is not defined, Elasticsearch
uses a GUID for the |
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This directive specifies the index to insert the event data into.
It must be a string type expression.
If the expression in the Index directive is not a constant string (it contains functions, field names, or operators), it will be evaluated for each event to be inserted.
The default is |
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This directive specifies the index type to use in the bulk index command. It must be a string type expression. If the expression in the IndexType directive is not a constant string (it contains functions, field names, or operators), it will be evaluated for each event to be inserted. By default, no index type is sent for compatibility with Elasticsearch 8.x. Index mapping types have been gradually deprecated starting with Elasticsearch 6.0.0, and support for them was completely removed in Elasticsearch 8.0.0. IndexType should only be used if required for Elasticsearch 7.x or older, or for custom types in Elasticsearch 8.x. See Removal of mapping types in the Elasticsearch Reference for more info. |
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Set this directive to the local port number to use for the connection, for example to satisfy a firewall rule that expects traffic from a known port. If you do not set this directive, the module uses a random high port number, which a firewall may block.
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This optional block directive can be used to specify a group of statements to handle errors reported by the Elasticsearch server for each document/record. All response status codes that are not between 200 and 299 are treated as errors. OnError can be used to perform custom error handling. For example, records that are rejected by the Elasticsearch server can be dropped or rerouted.
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This optional directive is used to specify the IP address (or hostname) and port number of the HTTP proxy server to be used.
The format is
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This directive has been deprecated. Please use the Proxy directive instead. |
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This directive has been deprecated. Please use the Proxy directive instead. |
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Set this directive to the number of seconds to wait between reconnection attempts. If you do not set this directive, the module starts with a 1 second interval and doubles it after each failed attempt, resetting to 1 second once it reconnects successfully.
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Set this directive to |
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Set this directive to
The default is |
Functions
The following functions are exported by om_elasticsearch.
- type: integer
get_response_code() -
Returns the response code for the current record. This function can only be used inside OnError Exec blocks.
- type: integer
get_retry_count() -
Returns the retry count for the current record. The retry count starts at
1when processing the first JSON response received for a ES request, and is incremented by1for every subsequent response for the same record. This function can only be used inside OnError Exec blocks.
Procedures
The following procedures are exported by om_elasticsearch.
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add_http_header(type: string name, type: string value); -
Dynamically add a custom HTTP header to HTTP requests.
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reconnect(); -
Force a reconnection. This can be used from a Schedule block to periodically reconnect to the server.
The reconnect() procedure must be used with caution. If configured, it can attempt to reconnect after every event sent, potentially overloading the destination system.
Examples
This configuration reads log records from file and forwards them to the Elasticsearch server on localhost. No further processing is done on the log records.
<Extension json>
Module xm_json
</Extension>
<Input file>
Module im_file
File '/var/log/myapp*.log'
BatchSize 200
BatchFlushInterval 2
# Parse log here if needed
# $EventTime should be set here
</Input>
<Output elasticsearch>
Module om_elasticsearch
URL http://localhost:9200/_bulk
# Create an index daily
Index strftime($EventTime, "nxlog-%Y%m%d")
# Or use the following if $EventTime is not set
# Index strftime(now(), "nxlog-%Y%m%d")
</Output>The following is a log record sample read by NXLog Agent.
Mar 24 15:58:53 pc1 systemd[1452]: tracker-store.service: Succeeded.The following is the JSON-formatted log record that will be sent to Elasticsearch.
{
"raw_event": "Mar 24 15:58:53 pc1 systemd[1452]: tracker-store.service: Succeeded."
}This configuration reads log records from a file and adds a $Hostname metadata field.
Log records are converted to JSON using the to_json() procedure of the xm_json module before they are forwarded to Elasticsearch.
<Extension json>
Module xm_json
</Extension>
<Input file>
Module im_file
File '/var/log/myapp*.log'
Exec $Hostname = hostname();
Exec $Message = $raw_event;
</Input>
<Output elasticsearch>
Module om_elasticsearch
URL http://localhost:9200/_bulk
Exec to_json();
</Output>The following is a log record sample read by NXLog Agent.
Mar 24 15:58:53 pc1 systemd[1452]: tracker-store.service: Succeeded.The following is the JSON-formatted log record that will be sent to Elasticsearch.
{
"EventReceivedTime": "2021-03-24T16:52:20.457348+01:00",
"SourceModuleName": "file",
"SourceModuleType": "im_file",
"Hostname": "pc1",
"Message": "Mar 24 15:58:53 pc1 systemd[1452]: tracker-store.service: Succeeded."
}This configuration reads syslog records from file. It uses the parse_syslog() procedure of the xm_syslog module to parse logs into structured data. Log records are then converted to JSON using the to_json() procedure of the xm_json module before they are forwarded to Elasticsearch.
<Extension syslog>
Module xm_syslog
</Extension>
<Extension json>
Module xm_json
</Extension>
<Input file>
Module im_file
File '/var/log/myapp*.log'
Exec parse_syslog();
</Input>
<Output elasticsearch>
Module om_elasticsearch
URL http://localhost:9200/_bulk
Exec to_json();
</Output>The following is a log record sample read by NXLog Agent.
Mar 24 15:58:53 pc1 systemd[1452]: tracker-store.service: Succeeded.The following is the JSON-formatted log record that will be sent to Elasticsearch.
{
"EventReceivedTime": "2021-03-24T16:30:18.920342+01:00",
"SourceModuleName": "file",
"SourceModuleType": "im_file",
"SyslogFacilityValue": 1,
"SyslogFacility": "USER",
"SyslogSeverityValue": 5,
"SyslogSeverity": "NOTICE",
"SeverityValue": 2,
"Severity": "INFO",
"Hostname": "pc1",
"EventTime": "2021-03-24T15:58:53.000000+01:00",
"SourceName": "systemd",
"ProcessID": 1452,
"Message": "tracker-store.service: Succeeded."
}This configuration reads JSON-formatted log records from a file.
It uses the parse_json() procedure of the xm_json module to parse logs into structured data and adds an $EventType metadata field.
Log records are then converted back to JSON using the to_json() procedure before they are forwarded to Elasticsearch.
<Extension json>
Module xm_json
</Extension>
<Input file>
Module im_file
File '/var/log/myapp*.log'
Exec parse_json();
Exec $EventType = "browser-history";
</Input>
<Output elasticsearch>
Module om_elasticsearch
URL http://localhost:9200/_bulk
Exec to_json();
</Output>The following is a log record sample read by NXLog Agent.
{
"AccessTime": "2021-03-24T16:30:43.000000+01:00",
"URL": "https://nxlog.co",
"Title": "High Performance Log Collection Solutions",
"Username": "user1"
}The following is the JSON-formatted log record that will be sent to Elasticsearch.
{
"EventReceivedTime": "2021-03-24T17:14:23.908155+01:00",
"SourceModuleName": "file",
"SourceModuleType": "im_file",
"AccessTime": "2021-03-24T16:30:43.000000+01:00",
"URL": "https://nxlog.co",
"Title": "High Performance Log Collection Solutions",
"Username": "user1",
"EventType": "browser-history"
}This configuration sends log records to an Elasticsearch server in a failover configuration (multiple URLs defined).
The actual destinations used in this case are http://localhost:9200/_bulk,http://192.168.1.1:9200/_bulk, and http://example.com:9200/_bulk.
<Extension json>
Module xm_json
</Extension>
<Output elasticsearch>
Module om_elasticsearch
URL http://localhost:9200/_bulk
URL http://192.168.1.1:9200/_bulk
URL http://example.com:9200/_bulk
</Output>This configuration collects all records that are failed to process by the Elastic server.
<Extension json>
Module xm_json
</Extension>
<Output elastic>
Module om_elasticsearch
URL http://localhost:9200/_bulk
Index strftime(now(), "test")
NoDefaultIndexType TRUE
DropOnError TRUE
<Exec>
json->to_json();
</Exec>
<OnRecordError>
<Exec>
$resp_code = get_response_code();
if $resp_code == 400
{
reroute("reroute_es_errors");
}
</Exec>
</OnRecordError>
</Output>
<Input null>
Module im_null
</Input>
<Output failed_es_logs>
Module om_file
File "/var/log/failed_es.logs"
</Output>
<Route reroute_es_errors>
Path null => failed_es_logs
</Route>