omrelp: RELP Output Module

tls.tlslib

Permits to specify the TLS library used by librelp. All relp protocol operations or actually performed by librelp and not rsyslog itself. This value specified is directly passed down to librelp. Depending on librelp version and build parameters, supported tls libraries differ (or TLS may not be supported at all). In this case rsyslog emits an error message.

Usually, the following options should be available: “openssl”, “gnutls”.

Note that “gnutls” is the current default for historic reasons. We actually recommend to use “openssl”. It provides better error messages and accepts a wider range of certificate types.

If you have problems with the default setting, we recommend to switch to “openssl”.

Target

The target server to connect to.

Port

Name or numerical value of TCP port to use when connecting to target.

Template

Defines the template to be used for the output.

Timeout

Timeout for relp sessions. If set too low, valid sessions may be considered dead and tried to recover.

Conn.Timeout

Timeout for the socket connection.

RebindInterval

Permits to specify an interval at which the current connection is broken and re-established. This setting is primarily an aid to load balancers. After the configured number of messages has been transmitted, the current connection is terminated and a new one started. This usually is perceived as a ``new connection’’ by load balancers, which in turn forward messages to another physical target system.

WindowSize

This is an expert parameter. It permits to override the RELP window size being used by the client. Changing the window size has both an effect on performance as well as potential message duplication in failure case. A larger window size means more performance, but also potentially more duplicated messages - and vice versa. The default 0 means that librelp’s default window size is being used, which is considered a compromise between goals reached. For your information: at the time of this writing, the librelp default window size is 128 messages, but this may change at any time. Note that there is no equivalent server parameter, as the client proposes and manages the window size in RELP protocol.

TLS

If set to “on”, the RELP connection will be encrypted by TLS, so that the data is protected against observers. Please note that both the client and the server must have set TLS to either “on” or “off”. Other combinations lead to unpredictable results.

Attention when using GnuTLS 2.10.x or older

Versions older than GnuTLS 2.10.x may cause a crash (Segfault) under certain circumstances. Most likely when an imrelp inputs and an omrelp output is configured. The crash may happen when you are receiving/sending messages at the same time. Upgrade to a newer version like GnuTLS 2.12.21 to solve the problem.

TLS.Compression

The controls if the TLS stream should be compressed (zipped). While this increases CPU use, the network bandwidth should be reduced. Note that typical text-based log records usually compress rather well.

TLS.PermittedPeer

Note: this parameter is mandatory depending on the value of TLS.AuthMode but the code does currently not check this.

Peer Places access restrictions on this forwarder. Only peers which have been listed in this parameter may be connected to. This guards against rouge servers and man-in-the-middle attacks. The validation bases on the certificate the remote peer presents.

This contains either remote system names or fingerprints, depending on the value of parameter TLS.AuthMode. One or more values may be entered.

When a non-permitted peer is connected to, the refusal is logged together with the given remote peer identify. This is especially useful in fingerprint authentication mode: if the administrator knows this was a valid request, he can simply add the fingerprint by copy and paste from the logfile to rsyslog.conf. It must be noted, though, that this situation should usually not happen after initial client setup and administrators should be alert in this case.

Note that usually a single remote peer should be all that is ever needed. Support for multiple peers is primarily included in support of load balancing scenarios. If the connection goes to a specific server, only one specific certificate is ever expected (just like when connecting to a specific ssh server). To specify multiple fingerprints, just enclose them in braces like this:

tls.permittedPeer=["SHA1:...1", "SHA1:....2"]

To specify just a single peer, you can either specify the string directly or enclose it in braces.

Note that in name authentication mode wildcards are supported. This can be done as follows:

tls.permittedPeer="*.example.com"

Of course, there can also be multiple names used, some with and some without wildcards:

tls.permittedPeer=["*.example.com", "srv1.example.net", "srv2.example.net"]

TLS.AuthMode

Sets the mode used for mutual authentication. Supported values are either “fingerprint” or “name”. Fingerprint mode basically is what SSH does. It does not require a full PKI to be present, instead self-signed certs can be used on all peers. Even if a CA certificate is given, the validity of the peer cert is NOT verified against it. Only the certificate fingerprint counts.

In “name” mode, certificate validation happens. Here, the matching is done against the certificate’s subjectAltName and, as a fallback, the subject common name. If the certificate contains multiple names, a match on any one of these names is considered good and permits the peer to talk to rsyslog.

The permitted names or fingerprints are configured via TLS.PermittedPeer.

TLS.CaCert

The CA certificate that can verify the machine certs.

TLS.MyCert

The machine public certificate.

TLS.MyPrivKey

The machine private key.

TLS.PriorityString

This parameter permits to specify the so-called “priority string” to GnuTLS. This string gives complete control over all crypto parameters, including compression setting. For this reason, when the prioritystring is specified, the “tls.compression” parameter has no effect and is ignored. Full information about how to construct a priority string can be found in the GnuTLS manual. At the time of this writing, this information was contained in section 6.10 of the GnuTLS manual. Note: this is an expert parameter. Do not use if you do not exactly know what you are doing.

tls.tlscfgcmd

The setting can be used if tls.tlslib is set to “openssl” to pass configuration commands to the openssl libray. OpenSSL Version 1.0.2 or higher is required for this feature. A list of possible commands and their valid values can be found in the documentation: https://www.openssl.org/docs/man1.0.2/man3/SSL_CONF_cmd.html

The setting can be single or multiline, each configuration command is separated by linefeed (n). Command and value are separated by equal sign (=). Here are a few samples:

LocalClientIp

Omrelp uses ip_address as local client address while connecting to remote logserver.