HTTP(s) (om_http)
This module connects to the specified URL in either plain HTTP or HTTPS mode. The module then waits for a response containing a successful status code (200, 201, or 202). All HTTP response codes other than 200, 201, and 202 are treated as errors, and by default, they are handled by resending the affected event records. If the remote host closes the connection or a timeout is exceeded while waiting for the response, it reconnects and retries the delivery. This HTTP-level acknowledgment ensures that no messages are lost during the transfer. By default, each event is transferred in a single POST request. However, the module can be configured to send event data in batches to reduce the latency caused by the HTTP responses, thus improving throughput.
Configuration
The om_http module accepts the following directives in addition to the common module directives. The URL directive is required.
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 on new lines, 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 fails 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 defined in the URL, it defaults to port 80 for HTTP and port 443 for HTTPS.
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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 or body part (in |
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This optional directive sets whether the event data should be sent as a single record per POST request or as a batch of multiple records per POST request. The accepted values are:
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Specifies the HTTP compression type for outgoing HTTP messages.
The possible values are Some HTTP servers may not accept compressed HTTP requests.
If a server doesn’t support a specific compression method, it may return a If an HTTP server supports RFC7694, the compression method specified by this directive is only used as a hint; if the server doesn’t support the same compression method, it uses the compression specified by the |
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This directive sets the Content-Type HTTP header to the string specified.
The Content-Type is set to one of
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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 HTTP errors. All HTTP response codes other than 200, 201 and 202 are treated as errors, and by default, they are handled by resending the affected event records. OnError can be used to perform custom error handling. For example, event records that are rejected by the receiver with a known HTTP error code, possibly due to unrecoverable formatting errors, can be dropped or rerouted. Note that if the original HTTP request contains multiple records (a batch), the rerouting breaks the batch up and sends one record per HTTP request. Only one OnError block directive can be specified per om_http module instance. The following sub-directives can be used inside this block.
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This boolean directive can be set to |
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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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This directive sets the HTTP request method.
The possible values are |
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Set this directive to
The default is |
Functions
The following functions are exported by om_http.
- type: string
get_full_request() -
Returns the last HTTP request sent to the remote endpoint. This function can only be used inside OnError Exec blocks. Note that due to batching, it may return the same result for multiple event records present in a batch.
- type: string
get_response_body() -
Returns the last received HTTP response message for the current record. Note that due to batching, the same response code value may be returned for multiple event records, when the retry count is
0. After the first HTTP error is received for a batch request, that request is split into separate requests per record, so the response code can be assumed to be per-record only when the retry count is greater than0. This function can only be used inside OnError Exec blocks. - type: integer
get_response_code() -
Returns the last received HTTP response code for the current record. Note that due to batching, the same response code value may be returned for multiple event records, when the retry count is
0. After the first HTTP error is received for a batch request, that request is split into separate requests per record, so the response code can be assumed to be per-record only when the retry count is greater than0. 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
0when processing the first HTTP response received for a batched 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_http.
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add_http_header(type: string name, type: string value); -
Dynamically add a custom HTTP header to HTTP requests.
This procedure impacts the way batching works. See the BatchMode directive for more information. -
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. -
set_http_request_path(type: string path); -
Set the path in the HTTP request to the specified string. The path value only replaces the path, query string, and fragment components of the URL, but not the hostname. This procedure is useful if the URL is dynamic and parameters such as the event ID need to be part of the URL. The specified string must be URL encoded if it contains reserved characters.
The following example results in
http://127.0.0.1:8888/testpath:URL http://127.0.0.1:8888/abcd Exec set_http_request_path("/testpath");This procedure impacts the way batching works. See the BatchMode directive for more information.
Examples
This configuration reads log messages from a file and forwards them via HTTPS.
<Output http>
Module om_http
URL https://server:8080/
AddHeader Auth-Token: 4ddf1d3c9
HTTPSCertFile %CERTDIR%/client-cert.pem
HTTPSCertKeyFile %CERTDIR%/client-key.pem
HTTPSCAFile %CERTDIR%/ca.pem
HTTPSAllowUntrusted FALSE
BatchMode multipart
</Output>This configuration sends logs via HTTPS in a failover configuration with multiple instances of the URL directive defined on new lines.
<Output http>
Module om_http
URL https://server:8080/
URL https://192.168.1.1:8080/
URL https://example.com:8080/
HTTPSCertFile %CERTDIR%/client-cert.pem
HTTPSCertKeyFile %CERTDIR%/client-key.pem
HTTPSCAFile %CERTDIR%/ca.pem
HTTPSAllowUntrusted FALSE
</Output>This configuration reads log messages from a file and forwards them via HTTP. An OnError block processes the response code and if the first retry fails, it performs one of these actions:
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If the HTTP status code is between 400 and 415, the record is converted to JSON and rerouted to file. NXLog Agent will not attempt to resend this record.
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If the HTTP status code is 700, the record is dropped. NXLog Agent will not attempt to resend this record.
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For any other HTTP status code, NXLog Agent will attempt to resend the record according to the RetryLimit sub-directive.
<Extension json>
Module xm_json
</Extension>
<Input file>
Module im_file
File 'input.log'
</Input>
<Output http>
Module om_http
URL http://192.168.1.10:8080/
<OnError>
RetryLimit 6
<Exec>
$response_code = get_response_code();
$retry_count = get_retry_count();
if $retry_count > 0
{
if $response_code >= 400 and $response_code <= 415
{
# 400 - 415: convert to JSON and reroute record
$event_message = $raw_event;
to_json();
reroute("reroute_errors");
}
else if $response_code == 700
{
# 700: drop record
drop();
}
}
</Exec>
</OnError>
</Output>
<Route file_to_http>
Path file => http
</Route>
<Input null>
Module im_null
</Input>
<Output failed_logs>
Module om_file
File 'failed.log'
</Output>
<Route reroute_errors>
Path null => failed_logs
</Route>The following JSON object shows an event that was rerouted to file by the configuration above.
{
"EventReceivedTime": "2021-08-11T11:49:48.570382+02:00",
"SourceModuleName": "input_file",
"SourceModuleType": "im_file",
"response_code": 401,
"retry_count": 1,
"event_message": "Aug 11 11:40:48 NXLog-Server-1 systemd[1]: Starting NXLog daemon..."
}