Microsoft Azure Sentinel (om_azure)
This module can be used to forward logs to Microsoft Azure applications. It can operate in three different modes to connect to the following data sources:
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Azure Table Storage
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Azure Blob Storage
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Azure Log Analytics workspace
It will connect to the URL specified in the configuration in either plain HTTP or HTTPS mode. Event data is sent in batches, reducing the latency caused by the HTTP responses, thus improving Microsoft Azure’s server performance.
| To examine the supported platforms, see the list of installer packages in the Available Modules chapter. |
Storage setup
For Blob or Table modes, Azure web application logging and storage can be configured from the Azure Management Portal by following these steps:
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After logging in to the Portal, open the left portal menu, select Storage accounts, and then select Create.
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Create the new storage account, providing a storage account name, region, and redundancy type. Take note of the storage name, you will need to specify this value in the NXLog configuration. More information on the storage settings can be found in the Microsoft documentation on how to Create a storage account.
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On the Review + create tab, click Create and wait for storage setup to complete.
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Navigate to your app and select App Service logs.
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Select On for Application Logging (Blob).
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Configure Storage Settings corresponding with the storage account created above. More information on the configuration settings can be found in the Microsoft documentation on how to Enable diagnostic logging for apps.
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Confirm the changes by clicking Save, then restart the service. Note that it may take a while for Azure to create the table and/or blob in the storage.
Log Analytics workspace setup
For Analytics mode, an application needs to be registered and
granted the necessary permissions to read from the Log Analytics workspace.
Follow these steps to create and configure the app from the
Azure Management Portal.
Register an Azure Active Directory application for NXLog:
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After logging in to the Portal, open the left portal menu, and select Azure Active Directory.
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Select App registrations and then + New registration.
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Provide an app name and select who can use the application, then click Register.
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Open the settings for your new app and take note of the Application (client) ID. You will need to specify this value for the ClientID directive.
Grant the app permission to use the Log Analytics API and create a client secret:
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From the left menu, select API permissions and then + Add a permission. Select APIs my organization uses and choose Log Analytics API.
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Select Application permissions for the type of permission required, and Data.Read for the permission.
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Click Add permissions to create the permission.
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From the left menu, select Certificates & secrets and then + New client secret. Enter a description and expiration period, then click Add.
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Take note of the Value of the new secret, you will need to specify this for the SharedKey directive.
Add the app to your Log Analytics workspace:
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Go to your Log Analytics workspace and take note of the Workspace ID. You will need to specify this value for the WorkspaceID directive.
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From the left menu, select Access control (IAM). Click + Add and select Add role assignments.
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Choose Log Analytics Reader for role, select the application registered above, and click Save.
For more information on the configuration settings see How to: Use the portal to create an Azure AD application in the Microsoft documentation, and the Microsoft Tech Community blog post on how to Access Azure Sentinel Log Analytics via API.
Output log format
om_azure in Table and Analytics modes 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-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 configuration examples of the above.
Configuration
The om_azure module accepts the following directives in addition to the common module directives.
Required directives
The following directives are required for the module to start.
This directive specifies the type of service the module should connect to.
It accepts one of the following values: |
Table mode
The following directives are required when using Table mode.
This directive specifies the authentication key to use for connecting to the Azure Storage account. |
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This directive specifies the name of the storage account to connect to. |
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The module will forward logs to this storage table. It must be a string-type expression. If the expression is not a constant string, i.e., it contains functions, field names, or operators, it will be evaluated for each event. If a table with the specified name doesn’t exist, om_azure will create it. The table name must only include letters and numbers. An expression that results in an invalid table name will cause an error and prevent events from being forwarded. |
Blob mode
The following are mandatory directives when using Blob mode.
This directive specifies the path of a single blob (formatted as |
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This directive specifies the authentication key to connect to the Azure Storage account. |
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This directive specifies the name of the storage account to connect to. |
Analytics mode
The following are mandatory directives when using Analytics mode.
This directive specifies the authentication key to connect to the Azure Storage account. |
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This directive specifies the name of a Custom Table that the module will send the logs to.
Azure automatically appends |
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This directive specifies the URL that the module will connect to. The module works in a failover configuration if additional URL directives are specified on new lines. If the first URL is unreachable, the module automatically fails over to the next one. If the last URL is unreachable, the module fails over to the first URL. The module operates in plain HTTP or HTTPS mode depending on the URL provided. If the port number is not explicitly defined, it defaults to port 80 for HTTP and port 443 for HTTPS. |
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This directive specifies the workspace ID of the Log Analytics account. |
HTTPS directives
The following directives configure secure data transfer via HTTPS.
Specifies if the connection should be allowed with an expired certificate.
If set to |
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Specifies if the certificate FQDN should be validated against the server hostname or not.
If set to |
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Specifies if the connection should be allowed without certificate verification.
If set to |
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The path to a directory containing certificate authority (CA) certificates. These certificates will be used to verify the certificate presented by the remote host. The certificate files must be named using the OpenSSL hashed format, i.e. the hash of the certificate followed by .0, .1 etc. To find the hash of a certificate using OpenSSL: For example, if the certificate hash is A remote host’s self-signed certificate (which is not signed by a CA) can also be trusted by including a copy of the certificate in this directory. The default operating system root certificate store will be used if this directive is not specified.
Unix-like operating systems commonly store root certificates in In addition, Microsoft’s PKI repository contains root certificates for Microsoft services. |
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The path of the certificate authority (CA) certificate that will be used to verify the certificate presented by the remote host. A remote host’s self-signed certificate (which is not signed by a CA) can be trusted by specifying the remote host certificate itself. In case of certificates signed by an intermediate CA, the certificate specified must contain the complete certificate chain (certificate bundle). |
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This optional directive, supported only on Windows, defines a pattern for locating a suitable CA (Certificate Authority) certificate and its thumbprint in the native Windows Certificate Storage.
The pattern must follow PCRE2 rules and use the format Configuration examples: or A normal log output example would look like as follows: |
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This optional directive, supported only on Windows, specifies the thumbprint of the certificate authority (CA) certificate that will be used to verify the certificate presented by the remote host. The hexadecimal fingerprint string can be copied from Windows Certificate Manager (certmgr.msc). Whitespaces are automatically removed. The certificate must be added to a Windows certificate store that is accessible by NXLog. This directive is mutually exclusive with the HTTPSCADir and HTTPSCAFile directives. |
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The path of the certificate file that will be presented to the remote host during the HTTPS handshake. |
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The path of the private key file that was used to generate the certificate specified by the HTTPSCertFile directive. This is used for the HTTPS handshake. |
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This optional directive, supported only on Windows, defines a pattern for identifying a corresponding certificate and its thumbprint within the native Windows Certificate Storage.
The pattern must follow PCRE2 rules and use the format Configuration examples: or A normal log output example would look like as follows: |
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This optional directive, supported only on Windows, specifies the thumbprint of the certificate that will be presented to the remote host during the HTTPS handshake.
The hexadecimal fingerprint string can be copied from Windows Certificate Manager (certmgr.msc).
Whitespaces are automatically removed.
The certificate must be imported to the When the global directive UseCNGCertificates is set to
On the contrary, when the global directive UseCNGCertificates is set to The usage of the directive is the same in all cases: |
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The path to a directory containing certificate revocation list (CRL) files. These CRL files will be used to check for certificates that were revoked and should no longer be accepted. The files must be named using the OpenSSL hashed format, i.e. the hash of the issuer followed by .r0, .r1 etc. To find the hash of the issuer of a CRL file using OpenSSL: For example if the hash is |
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The path of the certificate revocation list (CRL) which will be used to check for certificates that have been revoked and should no longer be accepted. Example to generate a CRL file using OpenSSL: |
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This optional directive specifies a file with dh-parameters for Diffie-Hellman key exchange. These parameters can be generated with dhparam(1ssl). If no directive is specified, default parameters will be used. See OpenSSL Wiki for further details. |
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The passphrase of the private key specified by the HTTPSCertKeyFile directive. A passphrase is required when the private key is encrypted. Example to generate a private key with Triple DES encryption using OpenSSL: This directive is not needed for passwordless private keys. |
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If set to This directive is only supported on Windows. |
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Specifies if the remote HTTPS host must present a certificate.
If set to |
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This optional directive, if set to This directive is only supported on Windows. |
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This optional directive can be used to set the permitted SSL cipher list, overriding the default.
Use the format described in the ciphers(1ssl) man page.
For example specify
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This optional directive can be used to set the permitted cipher list for TLSv1.3. Use the same format as in the HTTPSSSLCipher directive. Refer to the OpenSSL documentation for a list of valid TLS v1.3 cipher suites. The default value is:
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If set to
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This directive can be used to set the allowed SSL/TLS protocol(s).
It takes a comma-separated list of values which can be any of the following: |
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The signature algorithm parameter that is being sent to the Windows SSL library. Allowed values depend on the available encryption providers. This directive is only supported on Windows. |
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This optional directive specifies the hostname used for Server Name Indication (SNI) in HTTPS mode. If not specified, it defaults to the hostname in the URL directive. |
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If set to TRUE, the module uses the Windows Cryptography API: Next Generation (CNG) to access the private keys associated with certificates identified by a thumbprint. This directive is only supported on Windows. |
Optional directives
This optional directive specifies an additional header to be added to each HTTP request. |
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This optional directive specifies the URL for connecting to the storage account. The module works in a failover configuration if additional URL directives are specified on new lines. If the first URL is unreachable, the module automatically fails over to the next one. If the last URL is unreachable, the module fails over to the first URL. The module operates in plain HTTP or HTTPS mode depending on the URL provided. If the port number is not explicitly defined, it defaults to port 80 for HTTP and port 443 for HTTPS. |
Examples
This configuration reads log messages from file and forwards them to table storage. No further processing is done on the log records.
<Input file>
Module im_file
File 'log.txt'
</Input>
<Output azure>
Module om_azure
Mode Table
StorageName YOUR_STORAGE_NAME
SharedKey YOUR_SHARED_KEY
TableName "TableName"
AddHeader X-Custom : custom-value
Exec add_http_header("Y-Dynamic", "dynamic value");
</Output>This configuration reads log messages from file and forwards them to blob storage. No further processing is done on the log records.
<Input file>
Module im_file
File 'log.txt'
</Input>
<Output azure>
Module om_azure
Mode Blob
StorageName YOUR_STORAGE_NAME
SharedKey YOUR_SHARED_KEY
Blob "blob_container/blob_name"
AddHeader X-Custom : custom-value
Exec add_http_header("Y-Dynamic", "dynamic value");
</Output>This configuration reads log messages from file and forwards them via HTTPS to Microsoft Azure Log Analytics Workspaces. No further processing is done on the log records.
<Input file>
Module im_file
File 'log.txt'
</Input>
<Output azure>
Module om_azure
Mode Analytics
# Since the API uses HTTPS, SSL must be configured
HTTPSCAFile %CERTDIR%/ca.pem
WorkspaceID YOUR_WORKSPACE_ID
SharedKey YOUR_SHARED_KEY
TableName "CustomLogs"
AddHeader X-Custom : custom-value
Exec add_http_header("Y-Dynamic", "dynamic value");
</Output>The following is a log record sample read by NXLog.
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 Microsoft Azure.
{
"raw_event": "Mar 24 15:58:53 pc1 systemd[1452]: tracker-store.service: Succeeded."
}This configuration reads log records from 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 Microsoft Azure.
<Extension json>
Module xm_json
</Extension>
<Input file>
Module im_file
File '/path/to/log/file'
Exec $Hostname = hostname();
Exec $Message = $raw_event;
</Input>
<Output azure>
Module om_azure
Mode Analytics
# Since the API uses HTTPS, SSL must be configured
HTTPSCAFile %CERTDIR%/ca.pem
WorkspaceID YOUR_WORKSPACE_ID
SharedKey YOUR_SHARED_KEY
TableName "testImFileNative_dir"
Exec to_json();
</Output>The following is a log record sample read by NXLog.
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 Microsoft Azure.
{
"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 Microsoft Azure.
<Extension syslog>
Module xm_syslog
</Extension>
<Extension json>
Module xm_json
</Extension>
<Input file>
Module im_file
File '/path/to/log/file'
Exec parse_syslog();
</Input>
<Output azure>
Module om_azure
Mode Analytics
# Since the API uses HTTPS, SSL must be configured
HTTPSCAFile %CERTDIR%/ca.pem
WorkspaceID YOUR_WORKSPACE_ID
SharedKey YOUR_SHARED_KEY
TableName "testImFileNative_dir"
Exec to_json();
</Output>The following is a log record sample read by NXLog.
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 Microsoft Azure.
{
"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 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 Microsoft Azure.
<Extension json>
Module xm_json
</Extension>
<Input file>
Module im_file
File '/path/to/log/file'
Exec parse_json();
Exec $EventType = "browser-history";
</Input>
<Output azure>
Module om_azure
Mode Analytics
# Since the API uses HTTPS, SSL must be configured
HTTPSCAFile %CERTDIR%/ca.pem
WorkspaceID YOUR_WORKSPACE_ID
SharedKey YOUR_SHARED_KEY
TableName "testImFileNative_dir"
Exec to_json();
</Output>The following is a log record sample read by NXLog.
{
"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 the Microsoft Azure Sentinel server.
{
"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"
}
