The om_ssl module uses the OpenSSL library to provide an SSL/TLS transport. It behaves like the om_tcp module, except that an SSL handshake is performed at connection time and the data is received over a secure channel. Log messages transferred over plain TCP can be eavesdropped or even altered with a man-in-the-middle attack, while the om_ssl module provides a secure log message transport.
The om_ssl module accepts the following directives in addition to the common module directives. The Host directive is required.
The module connects to the IP address or hostname defined in this directive. If additional hosts 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 port number can be defined by appending it at the end of the hostname or IP address using a colon as a separator (
host:port). For each destination with no port number defined here, the port number specified in the Port directive is used. Port numbers defined here take precedence over any port number defined in the Port directive.
The module connects to the port number on the destination host defined in this directive. This configuration is only used for any destination that does not have a port number specified in the Host directive. If no port is configured for a destination in either directive, the default port is used, which is port 514.
|The Port directive is deprecated and will be removed from NXLog EE 6.0. After that, the port can only be defined in the Host directive.|
This boolean directive specifies whether the connection should be allowed with an expired certificate. If set to
TRUE, the connection will be allowed even if the remote server presents an expired certificate. The default is
FALSE: the remote server must present a certificate that is not expired.
This boolean directive specifies that the connection should be allowed regardless of the certificate verification results. If set to
TRUE, the connection will be allowed with any unexpired certificate provided by a server. The default value is
FALSE: the remote server must present a trusted certificate.
This directive specifies a path to a directory containing certificate authority (CA) certificates. These certificates will be used to verify the certificate presented by the remote server. 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:
$ openssl x509 -hash -noout -in ca.crt
For example if the certificate hash is
e2f14e4a, then the certificate filename should be
e2f14e4a.0. If there is another certificate with the same hash then it should be named
e2f14e4a.1and so on.
A remote server’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.
This specifies the path of the certificate authority (CA) certificate that will be used to verify the certificate presented by the remote server. A remote server’s self-signed certificate (which is not signed by a CA) can be trusted by specifying the remote server certificate itself. In case of certificates signed by an intermediate CA, the certificate specified must contain the complete certificate chain (certificate bundle).
This optional directive specifies the thumbprint of the certificate authority (CA) certificate that will be used to verify the certificate presented by the remote server. 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 only supported on Windows and is mutually exclusive with the CADir and CAFile directives.
This optional boolean directive, when set to
TRUE, enables the loading of all available Windows certificates into NXLog, for use during remote certificate verification. Any required certificates must be added to a Windows certificate store that NXLog can access. This directive is mutually exclusive with the CAThumbprint, CADir and CAFile directives.
This specifies the path of the certificate file that will be presented to the remote server during the SSL handshake.
This specifies the path of the private key file that was used to generate the certificate specified by the CertFile directive. This is used for the SSL handshake.
This optional directive specifies the thumbprint of the certificate that will be presented to the remote server during the SSL 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
Local Computer\Personalcertificate store in PFX format for NXLog to find it. 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
This directive is only supported on Windows and is mutually exclusive with the CertFile and CertKeyFile directives.
This directive specifies a 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:
$ openssl crl -hash -noout -in crl.pem
For example if the hash is
e2f14e4a, then the filename should be
e2f14e4a.r0. If there is another file with the same hash then it should be named
e2f14e4a.r1and so on.
This specifies 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:
$ openssl ca -gencrl -out crl.pem
This optional directive specifies a file with dh-parameters for Diffie-Hellman key exchange. These parameters can be generated with dhparam(1ssl). If this directive is not specified, default parameters will be used. See the OpenSSL Wiki for further details.
This directive specifies the passphrase of the private key specified by the CertKeyFile directive. A passphrase is required when the private key is encrypted. Example to generate a private key with Triple DES encryption using OpenSSL:
$ openssl genrsa -des3 -out server.key 2048
This directive is not needed for passwordless private keys.
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.
Due to the required
TIME-WAITdelay in closing connections, attempts to bind to
LocalPortmay fail. In such cases, the message
Address already in usewill be written to
nxlog.log. If the situation persists, it could impede network performance.
See the OutputType directive in the list of common module directives. The default is LineBased_LF.
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 doubles 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.
The Reconnect directive must be used with caution. If it is used on multiple systems, it can send reconnect requests simultaneously to the same destination, potentially overloading the destination system. It may also cause NXLog to use unusually high system resources or cause NXLog to become unresponsive.
This optional directive specifies the hostname used for Server Name Indication (SNI). If not specified, it defaults to the hostname in the Host directive.
This optional directive can be used to set the permitted cipher list for TLSv1.2 and below, overriding the default. Use the format described in the ciphers(1ssl) man page. For example specify
RSA:!COMPLEMENTOFALLto include all ciphers with RSA authentication but leave out ciphers without encryption.
|If RSA or DSA ciphers with Diffie-Hellman key exchange are used, DHFile can be set for specifying custom dh-parameters.|
This optional directive can be used to set the permitted cipher list for TLSv1.3. Use the same format as in the SSLCipher directive. Refer to the OpenSSL documentation for a list of valid TLS v1.3 cipher suites. The default value is:
This boolean directive allows you to enable data compression when sending data over the network. The compression mechanism is based on the zlib compression library. If the directive is not specified, it defaults to
FALSE: compression is disabled.
Some Linux packages (for example, Debian) use the OpenSSL library provided by the OS and may not support the zlib compression mechanism. The module will emit a warning on startup if the compression support is missing. The generic deb/rpm packages are bundled with a zlib-enabled libssl library.
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:
TLSv1.3. By default, the
TLSv1.3protocols are allowed. Note that the OpenSSL library shipped by Linux distributions may not support
SSLv3, and these will not work even if enabled with this directive.
This boolean directive is used to turn off the network optimization performed by Nagle’s algorithm. Nagle’s algorithm is a network optimization tweak that tries to reduce the number of small packets sent out to the network, by merging them into bigger frames, and by not sending them to the other side of the session before receiving the ACK. If this directive is unset, the TCP_NODELAY socket option will not be set.
The following procedures are exported by om_ssl.
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.
Pre-v5 syntax examples are included, they will become invalid with NXLog EE 6.0.
This configuration reads log messages from socket and sends them in the NXLog binary format to another NXLog agent.
<Input uds> Module im_uds UDS tmp/socket </Input> <Output ssl> Module om_ssl Host example.com:23456 CAFile %CERTDIR%/ca.pem CertFile %CERTDIR%/client-cert.pem CertKeyFile %CERTDIR%/client-key.pem KeyPass secret AllowUntrusted TRUE OutputType Binary </Output> # Using the syntax prior to NXLog EE 5, # where the port is defined in a separate directive. #<Output ssl> # Module om_ssl # Host example.com # Port 23456 # CAFile %CERTDIR%/ca.pem # CertFile %CERTDIR%/client-cert.pem # CertKeyFile %CERTDIR%/client-key.pem # KeyPass secret # AllowUntrusted TRUE # OutputType Binary #</Output>
This configuration sends logs to another NXLog agent in a failover configuration (multiple Hosts defined).
<Output ssl> Module om_ssl Host 192.168.1.2:23456 Host 192.168.1.3:23456 Host example.com:1514 CAFile %CERTDIR%/ca.pem </Output>