Cluster extensions for Sarama, the Go client library for Apache Kafka 0.9 (and later).
Documentation and example are available via godoc at http://godoc.org/github.com/bsm/sarama-cluster
Consumers have two modes of operation. In the default multiplexed mode messages (and errors) of multiple topics and partitions are all passed to the single channel:
package main
import (
"fmt"
"log"
"os"
"os/signal"
cluster "github.com/bsm/sarama-cluster"
)
func main() {
// init (custom) config, enable errors and notifications
config := cluster.NewConfig()
config.Consumer.Return.Errors = true
config.Group.Return.Notifications = true
// init consumer
brokers := []string{"127.0.0.1:9092"}
topics := []string{"my_topic", "other_topic"}
consumer, err := cluster.NewConsumer(brokers, "my-consumer-group", topics, config)
if err != nil {
panic(err)
}
defer consumer.Close()
// trap SIGINT to trigger a shutdown.
signals := make(chan os.Signal, 1)
signal.Notify(signals, os.Interrupt)
// consume errors
go func() {
for err := range consumer.Errors() {
log.Printf("Error: %s\n", err.Error())
}
}()
// consume notifications
go func() {
for ntf := range consumer.Notifications() {
log.Printf("Rebalanced: %+v\n", ntf)
}
}()
// consume messages, watch signals
for {
select {
case msg, ok := <-consumer.Messages():
if ok {
fmt.Fprintf(os.Stdout, "%s/%d/%d\t%s\t%s\n", msg.Topic, msg.Partition, msg.Offset, msg.Key, msg.Value)
consumer.MarkOffset(msg, "") // mark message as processed
}
case <-signals:
return
}
}
}Users who require access to individual partitions can use the partitioned mode which exposes access to partition-level consumers:
package main
import (
"fmt"
"log"
"os"
"os/signal"
cluster "github.com/bsm/sarama-cluster"
)
func main() {
// init (custom) config, set mode to ConsumerModePartitions
config := cluster.NewConfig()
config.Group.Mode = cluster.ConsumerModePartitions
// init consumer
brokers := []string{"127.0.0.1:9092"}
topics := []string{"my_topic", "other_topic"}
consumer, err := cluster.NewConsumer(brokers, "my-consumer-group", topics, config)
if err != nil {
panic(err)
}
defer consumer.Close()
// trap SIGINT to trigger a shutdown.
signals := make(chan os.Signal, 1)
signal.Notify(signals, os.Interrupt)
// consume partitions
for {
select {
case part, ok := <-consumer.Partitions():
if !ok {
return
}
// start a separate goroutine to consume messages
go func(pc cluster.PartitionConsumer) {
for msg := range pc.Messages() {
fmt.Fprintf(os.Stdout, "%s/%d/%d\t%s\t%s\n", msg.Topic, msg.Partition, msg.Offset, msg.Key, msg.Value)
consumer.MarkOffset(msg, "") // mark message as processed
}
}(part)
case <-signals:
return
}
}
}You need to install Ginkgo & Gomega to run tests. Please see http://onsi.github.io/ginkgo for more details.
To run tests, call:
$ make test
By default, sarama's Config.Consumer.Offsets.Initial is set to sarama.OffsetNewest. This means that in the event that a brand new consumer is created, and it has never committed any offsets to kafka, it will only receive messages starting from the message after the current one that was written.
If you wish to receive all messages (from the start of all messages in the topic) in the event that a consumer does not have any offsets committed to kafka, you need to set Config.Consumer.Offsets.Initial to sarama.OffsetOldest.
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