Documentation Grafana Agent Flow mode Reference Components reference loki.source.syslog

loki.source.syslog

loki.source.syslog listens for syslog messages over TCP or UDP connections and forwards them to other loki.* components. The messages must be compliant with the RFC5424 format.

The component starts a new syslog listener for each of the given config blocks and fans out incoming entries to the list of receivers in forward_to.

Multiple loki.source.syslog components can be specified by giving them different labels.

Usage

Alloy Copy

loki.source.syslog "LABEL" {
  listener {
    address = "LISTEN_ADDRESS"
  }
  ...

  forward_to = RECEIVER_LIST
}

Arguments

loki.source.syslog supports the following arguments:

The relabel_rules field can make use of the rules export value from a loki.relabel component to apply one or more relabeling rules to log entries before they’re forwarded to the list of receivers in forward_to.

Blocks

The following blocks are supported inside the definition of loki.source.syslog:

The > symbol indicates deeper levels of nesting. For example, config > tls_config refers to a tls_config block defined inside a config block.

listener block

The listener block defines the listen address and protocol where the listener expects syslog messages to be sent to, as well as its behavior when receiving messages.

The following arguments can be used to configure a listener. Only the address field is required and any omitted fields take their default values.

By default, the component assigns the log entry timestamp as the time it was processed.

The labels map is applied to every message that the component reads.

All header fields from the parsed RFC5424 messages are brought in as internal labels, prefixed with __syslog_.

If label_structured_data is set, structured data in the syslog header is also translated to internal labels in the form of __syslog_message_sd_<ID>_<KEY>. For example, a structured data entry of [example@99999 test="yes"] becomes the label __syslog_message_sd_example_99999_test with the value "yes".

tls_config block

Exported fields

loki.source.syslog does not export any fields.

Component health

loki.source.syslog is only reported as unhealthy if given an invalid configuration.

Debug information

loki.source.syslog exposes some debug information per syslog listener:

• Whether the listener is currently running.
• The listen address.
• The labels that the listener applies to incoming log entries.

Debug metrics

• loki_source_syslog_entries_total (counter): Total number of successful entries sent to the syslog component.
• loki_source_syslog_parsing_errors_total (counter): Total number of parsing errors while receiving syslog messages.
• loki_source_syslog_empty_messages_total (counter): Total number of empty messages received from the syslog component.

Example

This example listens for Syslog messages in valid RFC5424 format over TCP and UDP in the specified ports and forwards them to a loki.write component.

Alloy Copy

loki.source.syslog "local" {
  listener {
    address  = "127.0.0.1:51893"
    labels   = { component = "loki.source.syslog", protocol = "tcp" }
  }

  listener {
    address  = "127.0.0.1:51898"
    protocol = "udp"
    labels   = { component = "loki.source.syslog", protocol = "udp"}
  }

  forward_to = [loki.write.local.receiver]
}

loki.write "local" {
  endpoint {
    url = "loki:3100/api/v1/push"
  }
}

Compatible components

loki.source.syslog can accept arguments from the following components:

• Components that export Loki LogsReceiver