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 directives are 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. |
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 Agent. 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 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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This directive can be used to enable HTTP compression for outgoing HTTP messages.
The possible values are |
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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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This optional directive specifies the local port number of the connection. If this is not specified, a random high port number will be used, which is not always ideal in firewalled network environments.
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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 droppped 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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This optional directive sets the reconnect interval in seconds. If it is set, the module attempts to reconnect in every defined second. If it is not set, the reconnect interval will start at 1 second and double with every attempt. If the duration of the successful connection is greater than the current reconnect interval, then the reconnect interval will be reset to 1 sec.
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This optional directive defines the behavior when the connection with the remote host is lost.
When set to |
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This directive sets the HTTP request method.
The possible values are |
Functions
The following functions are exported by om_http.
- 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.
- 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.
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(string path);-
Set the path in the HTTP request to the string specified. This is useful if the URL is dynamic and parameters such as event ID need to be included in the URL. Note that the string must be URL encoded if it contains reserved characters.
This function 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:
-
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..."
}