Add static routing_key option to amqp output (#3994)

etc/telegraf.conf

@@ -168,8 +168,11 @@
 #   ## Using EXTERNAL requires enabling the rabbitmq_auth_mechanism_ssl plugin as
 #   ## described here: https://www.rabbitmq.com/plugins.html
 #   # auth_method = "PLAIN"
+#   ## Topic routing key
+#   # routing_key = ""
 #   ## Telegraf tag to use as a routing key
 #   ##  ie, if this tag exists, its value will be used as the routing key
+#   ##  and override routing_key config even if defined
 #   routing_tag = "host"
 #   ## Delivery Mode controls if a published message is persistent
 #   ## Valid options are "transient" and "persistent". default: "transient"
@@ -3630,4 +3633,3 @@
 # [[inputs.zipkin]]
 #   # path = "/api/v1/spans" # URL path for span data
 #   # port = 9411            # Port on which Telegraf listens
-

plugins/outputs/amqp/README.md

@@ -2,12 +2,18 @@
 
 This plugin writes to a AMQP 0-9-1 Exchange, a promenent implementation of this protocol being [RabbitMQ](https://www.rabbitmq.com/).
 
-Metrics are written to a topic exchange using tag, defined in configuration file as RoutingTag, as a routing key.
+Metrics are written to a topic exchange using a routing key defined by:
+1. The routing_key config defines a static value
+2. The routing_tag config defines a metric tag with a dynamic value, overriding the static routing_key if found
+3. If neither option is defined, or the tag is not found in a metric, then the empty routing key will be used
 
-If RoutingTag is empty, then empty routing key will be used.
-Metrics are grouped in batches by RoutingTag.
+Metrics are grouped in batches by the final routing key.
 
-This plugin doesn't bind exchange to a queue, so it should be done by consumer.
+This plugin doesn't bind exchange to a queue, so it should be done by consumer. The exchange is always defined as type: topic.
+To use it for distributing metrics equally among workers (type: direct), set the routing_key to a static value on the exchange,
+declare and bind a single queue with the same routing_key, and consume from the same queue in each worker.
+To use it to send metrics to many consumers at once (type: fanout), set the routing_key to "#" on the exchange, then declare, bind,
+and consume from individual queues in each worker.
 
 For an introduction to AMQP see:
 - https://www.rabbitmq.com/tutorials/amqp-concepts.html
@@ -26,8 +32,11 @@ For an introduction to AMQP see:
   ## Using EXTERNAL requires enabling the rabbitmq_auth_mechanism_ssl plugin as
   ## described here: https://www.rabbitmq.com/plugins.html
   # auth_method = "PLAIN"
+  ## Topic routing key
+  # routing_key = ""
   ## Telegraf tag to use as a routing key
   ##  ie, if this tag exists, its value will be used as the routing key
+  ##  and override routing_key config even if defined
   routing_tag = "host"
   ## Delivery Mode controls if a published message is persistent
   ## Valid options are "transient" and "persistent". default: "transient"

plugins/outputs/amqp/amqp.go

@@ -30,7 +30,9 @@ type AMQP struct {
 	Exchange string
 	// AMQP Auth method
 	AuthMethod string
-	// Routing Key Tag
+	// Routing Key (static)
+	RoutingKey string `toml:"routing_key"`
+	// Routing Key from Tag
 	RoutingTag string `toml:"routing_tag"`
 	// InfluxDB database
 	Database string
@@ -77,8 +79,11 @@ var sampleConfig = `
   ## Using EXTERNAL requires enabling the rabbitmq_auth_mechanism_ssl plugin as
   ## described here: https://www.rabbitmq.com/plugins.html
   # auth_method = "PLAIN"
+  ## Topic routing key
+  # routing_key = ""
   ## Telegraf tag to use as a routing key
   ##  ie, if this tag exists, its value will be used as the routing key
+  ##  and override routing_key config even if defined
   routing_tag = "host"
   ## Delivery Mode controls if a published message is persistent
   ## Valid options are "transient" and "persistent". default: "transient"
@@ -234,6 +239,9 @@ func (q *AMQP) Write(metrics []telegraf.Metric) error {
 
 	for _, metric := range metrics {
 		var key string
+		if q.RoutingKey != "" {
+			key = q.RoutingKey
+		}
 		if q.RoutingTag != "" {
 			if h, ok := metric.Tags()[q.RoutingTag]; ok {
 				key = h