refactor: ditch consumer groups for direct consumers (#35)

* refactor: replace consumer groups with direct consumers

* feat: make target channel buffer configurable

* fix: Fix stop at end flow

* fix: Fix filters config name while parsing

---------

Co-authored-by: Joe Paul <joeirimpan@gmail.com>

config.sample.toml

@@ -15,10 +15,6 @@ source_topic2 = "target_topic2"
 [source_pool]
 # Kafka client config common to all upstream sources ([[sources]]).
 initial_offset = "start"
-# Static memmbership to pin the member for the consumer group for respawn / reconnect and fence other members from connecting using the same id.
-instance_id = "client_instance_id"
-# Consumer group id.
-group_id = "consumer_group"
 
 # Frequency at which source servers are polled for health/lag.
 healthcheck_interval = "3s"
@@ -109,6 +105,7 @@ ca_cert_path = ""
 max_retries = -1
 flush_batch_size = 1000
 batch_size = 1000
+buffer_size = 100000 # channel buffer length
 max_message_bytes = 10000000
 
 # Kafka exponential retry-backoff config for reconnection attempts.

init.go

@@ -92,14 +92,12 @@ func initSourcePoolConfig(ko *koanf.Koanf) relay.SourcePoolCfg {
 		EnableBackoff:       ko.Bool("source_pool.backoff_enable"),
 		BackoffMin:          ko.MustDuration("source_pool.backoff_min"),
 		BackoffMax:          ko.MustDuration("source_pool.backoff_max"),
-		GroupID:             ko.MustString("source_pool.group_id"),
-		InstanceID:          ko.MustString("source_pool.instance_id"),
 	}
 }
 
 func initRelayConfig(ko *koanf.Koanf) relay.RelayCfg {
 	return relay.RelayCfg{
-		StopAtEnd: ko.Bool("stop_at_end"),
+		StopAtEnd: ko.Bool("stop-at-end"),
 	}
 }
 
@@ -175,10 +173,10 @@ func initTopicsMap(ko *koanf.Koanf) relay.Topics {
 }
 
 // initKafkaConfig reads the source(s)/target Kafka configuration.
-func initKafkaConfig(ko *koanf.Koanf) ([]relay.ConsumerGroupCfg, relay.ProducerCfg) {
+func initKafkaConfig(ko *koanf.Koanf) ([]relay.ConsumerCfg, relay.ProducerCfg) {
 	// Read source Kafka config.
 	src := struct {
-		Sources []relay.ConsumerGroupCfg `koanf:"sources"`
+		Sources []relay.ConsumerCfg `koanf:"sources"`
 	}{}
 
 	if err := ko.Unmarshal("", &src); err != nil {
@@ -237,11 +235,11 @@ func initFilters(ko *koanf.Koanf, lo *slog.Logger) (map[string]filter.Provider,
 		}
 
 		var cfg filter.Config
-		if err := ko.Unmarshal("filter."+id, &cfg); err != nil {
+		if err := ko.Unmarshal("filters."+id, &cfg); err != nil {
 			log.Fatalf("error unmarshalling filter config: %s: %v", id, err)
 		}
 		if cfg.Config == "" {
-			lo.Info(fmt.Sprintf("WARNING: No config 'filter.%s' for '%s' in config", id, id))
+			lo.Info(fmt.Sprintf("WARNING: No config 'filters.%s' for '%s' in config", id, id))
 		}
 
 		// Initialize the plugin.

internal/relay/config.go

@@ -42,8 +42,8 @@ type KafkaCfg struct {
 	EnableLog bool `koanf:"enable_log"`
 }
 
-// ConsumerGroupCfg is the consumer group specific config.
-type ConsumerGroupCfg struct {
+// ConsumerCfg is the direct consumer config.
+type ConsumerCfg struct {
 	KafkaCfg `koanf:",squash"`
 }
 
@@ -57,6 +57,7 @@ type ProducerCfg struct {
 	FlushFrequency    time.Duration `koanf:"flush_frequency"`
 	MaxMessageBytes   int           `koanf:"max_message_bytes"`
 	BatchSize         int           `koanf:"batch_size"`
+	BufferSize        int           `koanf:"buffer_size"`
 	FlushBatchSize    int           `koanf:"flush_batch_size"`
 	Compression       string        `koanf:"compression"` // gzip|snappy|lz4|zstd|none
 }

internal/relay/relay.go

@@ -12,7 +12,7 @@ import (
 )
 
 type RelayCfg struct {
-	StopAtEnd bool `koanf:"stop_at_end"`
+	StopAtEnd bool
 }
 
 // Relay represents the input, output kafka and the remapping necessary to forward messages from one topic to another.
@@ -30,7 +30,7 @@ type Relay struct {
 	// If stop-at-end is enabled, the "end" offsets of the source
 	// read at the time of boot are cached here to compare against
 	// live offsets and stop consumption.
-	targetOffsets map[string]map[int32]kgo.Offset
+	targetOffsets TopicOffsets
 
 	// Live topic offsets from source.
 	srcOffsets map[string]map[int32]int64
@@ -42,7 +42,7 @@ type Relay struct {
 func NewRelay(cfg RelayCfg, src *SourcePool, target *Target, topics Topics, filters map[string]filter.Provider, log *slog.Logger) (*Relay, error) {
 	// If stop-at-end is set, fetch and cache the offsets to determine
 	// when end is reached.
-	var offsets map[string]map[int32]kgo.Offset
+	var offsets TopicOffsets
 	if cfg.StopAtEnd {
 		if o, err := target.GetHighWatermark(); err != nil {
 			return nil, err
@@ -115,7 +115,7 @@ func (re *Relay) Start(globalCtx context.Context) error {
 	go func() {
 		defer wg.Done()
 		// Wait till main ctx is cancelled.
-		<-globalCtx.Done()
+		<-ctx.Done()
 
 		// Stop consumer group.
 		re.source.Close()
@@ -133,6 +133,7 @@ func (re *Relay) Start(globalCtx context.Context) error {
 	// Close producer.
 	re.target.Close()
 
+	cancel()
 	wg.Wait()
 
 	return nil
@@ -223,7 +224,7 @@ loop:
 				rec := iter.Next()
 				// Always record the latest offsets before the messages are processed for new connections and
 				// retries to consume from where it was left off.
-				// NOTE: What if the next step fails? The messages won't be read again?
+				// TODO: What if the next step fails? The messages won't be read again?
 				re.source.RecordOffsets(rec)
 
 				if err := re.processMessage(ctx, rec); err != nil {