module.river

argument "targets" { }

argument "hostname" {
	optional = true

	// Match static mode's behavior for how the hostname was determined, where
	// the $HOSTNAME environment variable took precedence over the
	// machine-reported hostname.
	default = coalesce(
		env("HOSTNAME"),
		constants.hostname,
	)
}

export "output" {
	value = discovery.relabel.host_filter.output
}

discovery.relabel "host_filter" {
	targets = argument.targets.value

	// Provide a set of labels which may indicate that the target comes from
	// the same host as the one Grafana Agent is running on.
	rule {
		source_labels = [
			// Labels from Consul SD.
			"__meta_consul_node",

			// Labels from Docker Swarm SD.
			"__meta_dockerswarm_node_id",
			"__meta_dockerswarm_node_hostname",
			"__meta_dockerswarm_node_address",

			// Labels from Kubernetes SD. Labels for `role: service` are omitted as
			// service targets have labels merged with discovered pods.
			"__meta_kubernetes_pod_node_name",
			"__meta_kubernetes_node_name",

			// Custom host label.
			"__host__",
		]

		// Our in-memory string will be something like A;B;C;D;E;F, where any of
		// the letters could be replaced with a label value or be empty if the
		// label value did not exist.
		//
		// We want to search for one of the following:
		//
		// - localhost or 127.0.0.1
		// - The hostname to check against.
		//
		// Where that text is either preceded by a colon (;B) or the start of the
		// string (A), and succeeded by a colon (B;) or the end of the string (F).
		regex = ".*(?:^|;)(localhost|127\\.0\\.0\\.1|" + argument.hostname.value + ")(?:;|$).*"

		action = "keep"
	}
}