WebHDFS (om_webhdfs)

This module is being phased out and will be removed in a future release. Use an external script instead.

This module allows logs to be stored in Hadoop HDFS using the WebHDFS protocol.

Configuration

The om_webhdfs module accepts the following directives in addition to the common module directives. The File and URL directives are required.

Required directives

The following directives are required for the module to start.

File

This mandatory directive specifies the name of the destination file. It must be a string type expression. If the expression in the File directive is not a constant string (it contains functions, field names, or operators), it will be evaluated before each request is dispatched to the WebHDFS REST endpoint (and after the Exec is evaluated). Note that the filename must be quoted to be a valid string literal, unlike in other directives which take a filename argument.

URL

This mandatory directive specifies the URL of the WebHDFS REST endpoint where the module should POST the event data. The module operates in plain HTTP or HTTPS mode depending on the URL provided, and connects to the hostname specified in the URL. If the port number is not explicitly indicated 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.

HTTPSAllowExpired

Set this directive to TRUE to allow connections with remote hosts presenting an expired certificate. The default is FALSE; the module rejects connections with expired certificates. This directive only takes effect when HTTPSRequireCert is set to TRUE.

HTTPSAllowHostnameValidation

Set this directive to TRUE to require that the certificate FQDN matches the server hostname before allowing a connection. The default is FALSE; the module does not validate the remote server hostname.

HTTPSAllowUntrusted

Set this directive to TRUE to allow connections with remote hosts regardless of certificate verification results. The default is FALSE; the module only accepts connections with trusted certificates.

HTTPSCADir

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 .0, .1, and so on. To find the hash of a certificate using OpenSSL:

$ openssl x509 -hash -noout -in ca.crt

For example, if the certificate hash is e2f14e4a, name the certificate file e2f14e4a.0. If there is another certificate with the same hash, name it e2f14e4a.1, and so on.

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 /etc/ssl/certs. Windows operating systems use the Windows Certificate Store, while macOS uses the Keychain Access Application as the default certificate store. See Certificate Authority (CA) certificates in the NXLog Platform User Guide for more information on using this directive.

In addition, Microsoft’s PKI repository contains root certificates for Microsoft services.

This directive is mutually exclusive with the HTTPSCAThumbprint, HTTPSCAPattern, and HTTPSSearchAllCertStores directives.

HTTPSCAFile

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.

HTTPSCAPattern

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:

SUBJECT=<value>, CN=<value>; DN=CN=<value>, O=<value>, OU=<value>, L=<value>, ST=<value>, C=<value>; SAN=<value>

The pattern doesn’t need to match every field. Include only the fields you want to match, and use .*? to skip over the rest.

For example, the following pattern matches only the DN and SAN fields:

HTTPSCAPattern    'DN=CN=SERVER01\.example\.com.*?SAN=DNS:SERVER01\.example\.com'

This produces the following output in the NXLog Agent log file:

matching pattern [DN=CN=SERVER01\.example\.com;.*?SAN=DNS:SERVER01\.example\.com] to certificate [SUBJECT=US, ClientState, ClientCity, ClientCompany, ClientUnit, SERVER01.example.com, CN=SERVER01.example.com; DN=CN=SERVER01.example.com, O=ClientCompany, OU=ClientUnit, L=ClientCity, ST=ClientState, C=US; SAN=DNS:SERVER01.example.com; DNS:www.SERVER01.example.com; IP:127.0.0.3; ]

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.

On macOS, keychain behavior and certificate requirements depend on your operating system version. Newer versions enforce stricter rules on certificate algorithms and key sizes. A certificate and private key may be imported into the keychain, yet remain unusable if they do not comply with the current macOS requirements. After importing, you may also need to give NXLog Agent permission to use the certificate in the keychain.

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

HTTPSCAThumbprint

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.

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

HTTPSCertFile

Set this directive to the path of the certificate file to present to the remote host during the HTTPS handshake.

HTTPSCertKeyFile

Set this directive to the path of the private key file corresponding to the certificate specified by HTTPSCertFile.

HTTPSCertPattern

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:

SUBJECT=<value>, CN=<value>; DN=CN=<value>, O=<value>, OU=<value>, L=<value>, ST=<value>, C=<value>; SAN=<value>

The pattern doesn’t need to match every field. Include only the fields you want to match, and use .*? to skip over the rest.

On Windows, import the certificate in PFX format into the Local Computer\Personal certificate store.

On macOS, ensure the certificate and its private key are present in the System Keychain (/Library/Keychains/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:

HTTPSCertPattern    $hostname + 'Cert'

HTTPSCertPattern    DN=CN=Client\.example\.com;.*?SAN=DNS:Client\.example\.com

This produces the following output in the NXLog Agent log file:

matching pattern [DN=CN=Client\.example\.com;.*?SAN=DNS:Client\.example\.com] to certificate [SUBJECT=US, ClientState, ClientCity, ClientCompany, ClientUnit, Client.example.com, CN=Client.example.com; DN=CN=Client.example.com, O=ClientCompany, OU=ClientUnit, L=ClientCity, ST=ClientState, C=US; SAN=DNS:Client.example.com; DNS:www.Client.example.com; IP:127.0.0.3; ]

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

HTTPSCertThumbprint

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 Local Computer\Personal certificate store in PFX format. To create a PFX file from the certificate and private key using OpenSSL:

$ openssl pkcs12 -export -out server.pfx -inkey server.key -in server.pem

When the global directive UseCNGCertificates is set to FALSE, the private key must be exportable.

If you generate the certificate request using Windows Certificate Manager, enable the Make private key exportable option from the certificate properties.
If you import the certificate with the Windows Certificate Import Wizard, make sure that the Mark this key as exportable option is enabled.
If you migrate the certificate and associated private key from one Windows machine to another, select Yes, export the private key when exporting from the source machine.

When UseCNGCertificates is set to TRUE, the private key does not need to be exportable. For example, private keys stored on a TPM are always non-exportable.

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 (/Library/Keychains/System.keychain).

For example:

HTTPSCertThumbprint    7c2cc5a5fb59d4f46082a510e74df17da95e2152

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

HTTPSCRLDir

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 .r0, .r1, and so on. To find the hash of the issuer of a CRL file using OpenSSL:

$ openssl crl -hash -noout -in crl.pem

For example, if the hash is e2f14e4a, name the file e2f14e4a.r0. If there is another file with the same hash, name it e2f14e4a.r1, and so on.

HTTPSCRLFile

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:

$ openssl ca -gencrl -out crl.pem

HTTPSDHFile

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.

HTTPSKeyPass

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:

$ openssl genrsa -des3 -out server.key 2048

HTTPSLoadCertificateChains

Set this directive to TRUE to load the full certificate chain from the PEM file referenced by HTTPSCertFile, which may contain a single certificate or the complete chain. The default is FALSE; the module loads certificates from the operating system certificate store instead.

This directive is only supported on Windows.

HTTPSRequireCert

Set this directive to TRUE to require the remote host to present a certificate during the HTTPS handshake. The module refuses the connection if no certificate is presented. The default is TRUE.

HTTPSSearchAllCertStores

Set this directive to TRUE to load all available Windows certificates into NXLog Agent for use during remote certificate verification. Any required certificates must be in a Windows certificate store accessible by NXLog Agent. This directive is only supported on Windows and is mutually exclusive with the HTTPSCAThumbprint, HTTPSCAPattern, HTTPSCADir, and HTTPSCAFile directives.

HTTPSSSLCipher

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 RSA:!COMPLEMENTOFALL to include all ciphers with RSA authentication but exclude ciphers without encryption.

If RSA or DSA ciphers with Diffie-Hellman key exchange are used, set HTTPSDHFile to specify custom Diffie-Hellman parameters.

HTTPSSSLCiphersuites

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:

TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256

HTTPSSSLCompression

Set this directive to TRUE to compress data using zlib when sending over the network. The default is FALSE; the module sends data without compression.

Some Linux distributions, including Debian, provide an OpenSSL library without zlib support. The module emits a warning on startup if compression support is missing. The generic deb/rpm packages are bundled with a zlib-enabled libssl library.

HTTPSSSLProtocol

Set this directive to restrict the TLS/SSL protocols the module accepts. Specify a comma-separated list of the following values: SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2, and TLSv1.3. The default is TLSv1.2 and TLSv1.3. The OpenSSL library shipped by some Linux distributions does not support SSLv2 and SSLv3; these protocols will not work even if specified here.

HTTPSTLSCertLog

Set this directive to TRUE to log the remote host’s certificate details during the HTTPS handshake. When available, the module logs the Subject, Issuer, NotBefore, and NotAfter fields to the NXLog Agent log file. The default is FALSE.

This directive depends on the values of the HTTPSAllowUntrusted and HTTPSRequireCert directives:

HTTPSAllowUntrusted HTTPSRequireCert Outcome

FALSE

Output depends on HTTPSTLSCertLog value

FALSE

TRUE

Output depends on HTTPSTLSCertLog value

TRUE

FALSE

No output regardless of HTTPSTLSCertLog value

TRUE

Output depends on HTTPSTLSCertLog value

Sigalgs

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.

SNI

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.

UseCNGCertificates

Set this directive to TRUE to use the Windows Cryptography API: Next Generation (CNG) to access the private keys of certificates identified by a thumbprint. This directive is only supported on Windows.

Optional directives

FlushInterval

The module will send the data to the endpoint defined in URL after this amount of time in seconds, unless FlushLimit is reached first. This defaults to 5 seconds.

FlushLimit

When the number of events in the output buffer reaches the value specified by this directive, the module will send the data to the endpoint defined in URL. This defaults to 500 events. The FlushInterval may trigger sending the write request before this limit is reached if the log volume is low to ensure that data is sent promptly.

QueryParam

This configuration option can be used to specify additional HTTP Query Parameters such as BlockSize. This option may be used to define more than one parameter:

QueryParam blocksize 42
QueryParam destination /foo

Reconnect

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.

Setting this directive on multiple systems can cause them to send reconnection requests to the same destination at the same time, potentially overloading it. This can also cause NXLog Agent to consume unusually high system resources or become unresponsive.

ReconnectOnData

Set this directive to TRUE to have the module reconnect to the remote host only when it has data to send, instead of keeping the connection open at all times. The default is FALSE; the module always keeps a connection open with the remote host.

Procedures

The following procedures are exported by om_webhdfs.

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

Example 1. Sending Logs to a WebHDFS Server

This example output module instance forwards messages to the specified URL and file using the WebHDFS protocol.

nxlog.conf

<Output hdfs>
   Module       om_webhdfs
   URL          http://hdfsserver.domain.com/
   File         "myfile"
   QueryParam   blocksize 42
   QueryParam   destination /foo
</Output>