Otel receivers spawn on need

CHANGELOG.md

@@ -41,6 +41,8 @@ Main (unreleased)
 
 - Fixed issue where text labels displayed outside of component node's boundary. (@hainenber)
 
+- Fix a bug where a topic was claimed by the wrong consumer type in `otelcol.receiver.kafka`. (@wildum)
+
 - Fix an issue where nested import.git config blocks could conflict if they had the same labels. (@wildum)
 
 - In `mimir.rules.kubernetes`, fix an issue where unrecoverable errors from the Mimir API were retried. (@56quarters)

docs/sources/reference/components/otelcol.receiver.kafka.md

@@ -40,13 +40,23 @@ Name | Type | Description | Default | Required
 ---- | ---- | ----------- | ------- | --------
 `brokers` | `array(string)` | Kafka brokers to connect to. | | yes
 `protocol_version` | `string` | Kafka protocol version to use. | | yes
-`topic` | `string` | Kafka topic to read from. | `"otlp_spans"` | no
+`topic` | `string` | Kafka topic to read from. | | no
 `encoding` | `string` | Encoding of payload read from Kafka. | `"otlp_proto"` | no
 `group_id` | `string` | Consumer group to consume messages from. | `"otel-collector"` | no
 `client_id` | `string` | Consumer client ID to use. | `"otel-collector"` | no
 `initial_offset` | `string` | Initial offset to use if no offset was previously committed. | `"latest"` | no
 `resolve_canonical_bootstrap_servers_only` | `bool` | Whether to resolve then reverse-lookup broker IPs during startup. | `"false"` | no
 
+If `topic` is not set, different topics will be used for different telemetry signals:
+
+* Metrics will be received from an `otlp_metrics` topic.
+* Traces will be received from an `otlp_spans` topic.
+* Logs will be received from an `otlp_logs` topic.
+
+If `topic` is set to a specific value, then only the signal type that corresponds to the data stored in the topic must be set in the output block.
+For example, if `topic` is set to `"my_telemetry"`, then the `"my_telemetry"` topic can only contain either metrics, logs, or traces. 
+If it contains only metrics, then `otelcol.receiver.kafka` should be configured to output only metrics.
+
 The `encoding` argument determines how to decode messages read from Kafka.
 `encoding` must be one of the following strings:
 

internal/component/otelcol/receiver/kafka/kafka.go

@@ -2,6 +2,8 @@
 package kafka
 
 import (
+	"fmt"
+	"strings"
 	"time"
 
 	"github.com/grafana/alloy/internal/component"
@@ -63,7 +65,6 @@ func (args *Arguments) SetToDefault() {
 		// for compatibility, even though that means using a client and group ID of
 		// "otel-collector".
 
-		Topic:         "otlp_spans",
 		Encoding:      "otlp_proto",
 		Brokers:       []string{"localhost:9092"},
 		ClientID:      "otel-collector",
@@ -77,6 +78,27 @@ func (args *Arguments) SetToDefault() {
 	args.DebugMetrics.SetToDefault()
 }
 
+// Validate implements syntax.Validator.
+func (args *Arguments) Validate() error {
+	var signals []string
+
+	if len(args.Topic) > 0 {
+		if len(args.Output.Logs) > 0 {
+			signals = append(signals, "logs")
+		}
+		if len(args.Output.Metrics) > 0 {
+			signals = append(signals, "metrics")
+		}
+		if len(args.Output.Traces) > 0 {
+			signals = append(signals, "traces")
+		}
+		if len(signals) > 1 {
+			return fmt.Errorf("only one signal can be set in the output block when a Kafka topic is explicitly set; currently set signals: %s", strings.Join(signals, ", "))
+		}
+	}
+	return nil
+}
+
 // Convert implements receiver.Arguments.
 func (args Arguments) Convert() (otelcomponent.Config, error) {
 	input := make(map[string]interface{})

internal/component/otelcol/receiver/kafka/kafka_test.go

@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"github.com/grafana/alloy/internal/component/otelcol"
+	"github.com/grafana/alloy/internal/component/otelcol/internal/fakeconsumer"
 	"github.com/grafana/alloy/internal/component/otelcol/receiver/kafka"
 	"github.com/grafana/alloy/syntax"
 	"github.com/mitchellh/mapstructure"
@@ -29,7 +30,6 @@ func TestArguments_UnmarshalAlloy(t *testing.T) {
 			expected: kafkareceiver.Config{
 				Brokers:         []string{"10.10.10.10:9092"},
 				ProtocolVersion: "2.0.0",
-				Topic:           "otlp_spans",
 				Encoding:        "otlp_proto",
 				GroupID:         "otel-collector",
 				ClientID:        "otel-collector",
@@ -153,7 +153,6 @@ func TestArguments_Auth(t *testing.T) {
 			expected: map[string]interface{}{
 				"brokers":          []string{"10.10.10.10:9092"},
 				"protocol_version": "2.0.0",
-				"topic":            "otlp_spans",
 				"encoding":         "otlp_proto",
 				"group_id":         "otel-collector",
 				"client_id":        "otel-collector",
@@ -205,7 +204,6 @@ func TestArguments_Auth(t *testing.T) {
 			expected: map[string]interface{}{
 				"brokers":          []string{"10.10.10.10:9092"},
 				"protocol_version": "2.0.0",
-				"topic":            "otlp_spans",
 				"encoding":         "otlp_proto",
 				"group_id":         "otel-collector",
 				"client_id":        "otel-collector",
@@ -263,7 +261,6 @@ func TestArguments_Auth(t *testing.T) {
 			expected: map[string]interface{}{
 				"brokers":          []string{"10.10.10.10:9092"},
 				"protocol_version": "2.0.0",
-				"topic":            "otlp_spans",
 				"encoding":         "otlp_proto",
 				"group_id":         "otel-collector",
 				"client_id":        "otel-collector",
@@ -320,7 +317,6 @@ func TestArguments_Auth(t *testing.T) {
 			expected: map[string]interface{}{
 				"brokers":          []string{"10.10.10.10:9092"},
 				"protocol_version": "2.0.0",
-				"topic":            "otlp_spans",
 				"encoding":         "otlp_proto",
 				"group_id":         "otel-collector",
 				"client_id":        "otel-collector",
@@ -433,3 +429,32 @@ func TestDebugMetricsConfig(t *testing.T) {
 		})
 	}
 }
+
+func TestArguments_Validate(t *testing.T) {
+	cfg := `
+		brokers = ["10.10.10.10:9092"]
+		protocol_version = "2.0.0"
+		topic = "traces"
+		output {
+		}
+	`
+	var args kafka.Arguments
+	require.NoError(t, syntax.Unmarshal([]byte(cfg), &args))
+
+	// Adding two traces consumer, expect no error
+	tracesConsumer := fakeconsumer.Consumer{}
+	args.Output.Traces = append(args.Output.Traces, &tracesConsumer)
+	tracesConsumer2 := fakeconsumer.Consumer{}
+	args.Output.Traces = append(args.Output.Traces, &tracesConsumer2)
+	require.NoError(t, args.Validate())
+
+	// Adding another signal type
+	logsConsumer := fakeconsumer.Consumer{}
+	args.Output.Logs = append(args.Output.Logs, &logsConsumer)
+	require.ErrorContains(t, args.Validate(), "only one signal can be set in the output block when a Kafka topic is explicitly set; currently set signals: logs, traces")
+
+	// Adding another signal type
+	metricsConsumer := fakeconsumer.Consumer{}
+	args.Output.Metrics = append(args.Output.Metrics, &metricsConsumer)
+	require.ErrorContains(t, args.Validate(), "only one signal can be set in the output block when a Kafka topic is explicitly set; currently set signals: logs, metrics, traces")
+}

internal/component/otelcol/receiver/receiver.go

@@ -149,36 +149,40 @@ func (r *Receiver) Update(args component.Arguments) error {
 		return err
 	}
 
-	var (
-		next        = rargs.NextConsumers()
-		nextTraces  = fanoutconsumer.Traces(next.Traces)
-		nextMetrics = fanoutconsumer.Metrics(next.Metrics)
-		nextLogs    = fanoutconsumer.Logs(next.Logs)
-	)
+	next := rargs.NextConsumers()
 
 	// Create instances of the receiver from our factory for each of our
 	// supported telemetry signals.
 	var components []otelcomponent.Component
 
-	tracesReceiver, err := r.factory.CreateTracesReceiver(r.ctx, settings, receiverConfig, nextTraces)
-	if err != nil && !errors.Is(err, otelcomponent.ErrDataTypeIsNotSupported) {
-		return err
-	} else if tracesReceiver != nil {
-		components = append(components, tracesReceiver)
+	if len(next.Traces) > 0 {
+		nextTraces := fanoutconsumer.Traces(next.Traces)
+		tracesReceiver, err := r.factory.CreateTracesReceiver(r.ctx, settings, receiverConfig, nextTraces)
+		if err != nil && !errors.Is(err, otelcomponent.ErrDataTypeIsNotSupported) {
+			return err
+		} else if tracesReceiver != nil {
+			components = append(components, tracesReceiver)
+		}
 	}
 
-	metricsReceiver, err := r.factory.CreateMetricsReceiver(r.ctx, settings, receiverConfig, nextMetrics)
-	if err != nil && !errors.Is(err, otelcomponent.ErrDataTypeIsNotSupported) {
-		return err
-	} else if metricsReceiver != nil {
-		components = append(components, metricsReceiver)
+	if len(next.Metrics) > 0 {
+		nextMetrics := fanoutconsumer.Metrics(next.Metrics)
+		metricsReceiver, err := r.factory.CreateMetricsReceiver(r.ctx, settings, receiverConfig, nextMetrics)
+		if err != nil && !errors.Is(err, otelcomponent.ErrDataTypeIsNotSupported) {
+			return err
+		} else if metricsReceiver != nil {
+			components = append(components, metricsReceiver)
+		}
 	}
 
-	logsReceiver, err := r.factory.CreateLogsReceiver(r.ctx, settings, receiverConfig, nextLogs)
-	if err != nil && !errors.Is(err, otelcomponent.ErrDataTypeIsNotSupported) {
-		return err
-	} else if logsReceiver != nil {
-		components = append(components, logsReceiver)
+	if len(next.Logs) > 0 {
+		nextLogs := fanoutconsumer.Logs(next.Logs)
+		logsReceiver, err := r.factory.CreateLogsReceiver(r.ctx, settings, receiverConfig, nextLogs)
+		if err != nil && !errors.Is(err, otelcomponent.ErrDataTypeIsNotSupported) {
+			return err
+		} else if logsReceiver != nil {
+			components = append(components, logsReceiver)
+		}
 	}
 
 	// Schedule the components to run once our component is running.

internal/component/otelcol/receiver/receiver_test.go

@@ -57,6 +57,74 @@ func TestReceiver(t *testing.T) {
 	require.NoError(t, waitTracesTrigger.Wait(time.Second), "consumer did not get invoked")
 }
 
+func TestReceiverNotStarted(t *testing.T) {
+	var (
+		waitConsumerTrigger = util.NewWaitTrigger()
+		onTracesConsumer    = func(t otelconsumer.Traces) {
+			waitConsumerTrigger.Trigger()
+		}
+	)
+	te := newTestEnvironment(t, onTracesConsumer)
+	te.Start(fakeReceiverArgs{
+		Output: &otelcol.ConsumerArguments{},
+	})
+
+	// Check that no trace receiver was started because it's not needed by the output.
+	require.ErrorContains(t, waitConsumerTrigger.Wait(time.Second), "context deadline exceeded")
+}
+
+func TestReceiverUpdate(t *testing.T) {
+	var (
+		consumer otelconsumer.Traces
+
+		waitConsumerTrigger = util.NewWaitTrigger()
+		onTracesConsumer    = func(t otelconsumer.Traces) {
+			consumer = t
+			waitConsumerTrigger.Trigger()
+		}
+
+		waitTracesTrigger = util.NewWaitTrigger()
+		nextConsumer      = &fakeconsumer.Consumer{
+			ConsumeTracesFunc: func(context.Context, ptrace.Traces) error {
+				waitTracesTrigger.Trigger()
+				return nil
+			},
+		}
+	)
+
+	te := newTestEnvironment(t, onTracesConsumer)
+	te.Start(fakeReceiverArgs{
+		Output: &otelcol.ConsumerArguments{},
+	})
+
+	// Check that no trace receiver was started because it's not needed by the output.
+	require.ErrorContains(t, waitConsumerTrigger.Wait(time.Second), "context deadline exceeded")
+
+	te.Controller.Update(fakeReceiverArgs{
+		Output: &otelcol.ConsumerArguments{
+			Traces: []otelcol.Consumer{nextConsumer},
+		},
+	})
+
+	// Now the trace receiver is started.
+	require.NoError(t, waitConsumerTrigger.Wait(time.Second), "no traces consumer sent")
+
+	err := consumer.ConsumeTraces(context.Background(), ptrace.NewTraces())
+	require.NoError(t, err)
+
+	require.NoError(t, waitTracesTrigger.Wait(time.Second), "consumer did not get invoked")
+
+	waitConsumerTrigger = util.NewWaitTrigger()
+
+	// Remove the trace receiver.
+	te.Controller.Update(fakeReceiverArgs{
+		Output: &otelcol.ConsumerArguments{},
+	})
+
+	// Check that after the update no trace receiver is started.
+	require.ErrorContains(t, waitConsumerTrigger.Wait(time.Second), "context deadline exceeded")
+}
+
 type testEnvironment struct {
 	t *testing.T
 

internal/converter/internal/otelcolconvert/testdata/kafka.alloy

@@ -1,7 +1,6 @@
 otelcol.receiver.kafka "default" {
 	brokers          = ["broker:9092"]
 	protocol_version = "2.0.0"
-	topic            = ""
 
 	authentication {
 		plaintext {