confluent-kafka-go

README

Confluent's Golang Client for Apache Kafka^TM

confluent-kafka-go is Confluent's Golang client for Apache Kafka and the Confluent Platform.

Features:

• High performance - confluent-kafka-go is a lightweight wrapper around librdkafka, a finely tuned C client.

• Reliability - There are a lot of details to get right when writing an Apache Kafka client. We get them right in one place (librdkafka) and leverage this work across all of our clients (also confluent-kafka-python and confluent-kafka-dotnet).

• Supported - Commercial support is offered by Confluent.

• Future proof - Confluent, founded by the creators of Kafka, is building a streaming platform with Apache Kafka at its core. It's high priority for us that client features keep pace with core Apache Kafka and components of the Confluent Platform.

The Golang bindings provides a high-level Producer and Consumer with support for the balanced consumer groups of Apache Kafka 0.9 and above.

See the API documentation for more information.

License: Apache License v2.0

Examples

High-level balanced consumer

import (
	"fmt"
	"github.com/confluentinc/confluent-kafka-go/kafka"
)

func main() {

	c, err := kafka.NewConsumer(&kafka.ConfigMap{
		"bootstrap.servers": "localhost",
		"group.id":          "myGroup",
		"auto.offset.reset": "earliest",
	})

	if err != nil {
		panic(err)
	}

	c.SubscribeTopics([]string{"myTopic", "^aRegex.*[Tt]opic"}, nil)

	for {
		msg, err := c.ReadMessage(-1)
		if err == nil {
			fmt.Printf("Message on %s: %s\n", msg.TopicPartition, string(msg.Value))
		} else {
			// The client will automatically try to recover from all errors.
			fmt.Printf("Consumer error: %v (%v)\n", err, msg)
		}
	}

	c.Close()
}

Producer

import (
	"fmt"
	"github.com/confluentinc/confluent-kafka-go/kafka"
)

func main() {

	p, err := kafka.NewProducer(&kafka.ConfigMap{"bootstrap.servers": "localhost"})
	if err != nil {
		panic(err)
	}

	defer p.Close()

	// Delivery report handler for produced messages
	go func() {
		for e := range p.Events() {
			switch ev := e.(type) {
			case *kafka.Message:
				if ev.TopicPartition.Error != nil {
					fmt.Printf("Delivery failed: %v\n", ev.TopicPartition)
				} else {
					fmt.Printf("Delivered message to %v\n", ev.TopicPartition)
				}
			}
		}
	}()

	// Produce messages to topic (asynchronously)
	topic := "myTopic"
	for _, word := range []string{"Welcome", "to", "the", "Confluent", "Kafka", "Golang", "client"} {
		p.Produce(&kafka.Message{
			TopicPartition: kafka.TopicPartition{Topic: &topic, Partition: kafka.PartitionAny},
			Value:          []byte(word),
		}, nil)
	}

	// Wait for message deliveries before shutting down
	p.Flush(15 * 1000)
}

More elaborate examples are available in the examples directory, including how to configure the Go client for use with Confluent Cloud.

Getting Started

Installing librdkafka

This client for Go depends on librdkafka v1.0.0 or later, so you either need to install librdkafka through your OS/distributions package manager, or download and build it from source.

• For Debian and Ubuntu based distros, install librdkafka-dev from the standard repositories or using Confluent's Deb repository.
• For Redhat based distros, install librdkafka-devel using Confluent's YUM repository.
• For MacOS X, install librdkafka from Homebrew. You may also need to brew install pkg-config if you don't already have it. brew install librdkafka pkg-config.
• For Windows, see the librdkafka.redist NuGet package.

Build from source:

git clone https://github.com/edenhill/librdkafka.git
cd librdkafka
./configure --prefix /usr
make
sudo make install

Install the client

go get -u github.com/confluentinc/confluent-kafka-go/kafka

See the examples for usage details.

Note that the development of librdkafka and the Go client are kept in synch. So if you use HEAD on master of the Go client, then you need to use HEAD on master of librdkafka. See this issue for more details.

API Strands

There are two main API strands: function and channel based.

Function Based Consumer

Messages, errors and events are polled through the consumer.Poll() function.

Pros:

• More direct mapping to underlying librdkafka functionality.

Cons:

• Makes it harder to read from multiple channels, but a go-routine easily solves that (see Cons in channel based consumer above about outdated events).
• Slower than the channel consumer.

See examples/consumer_example

Channel Based Consumer (deprecated)

Deprecated: The channel based consumer is deprecated due to the channel issues mentioned below. Use the function based consumer.

Messages, errors and events are posted on the consumer.Events channel for the application to read.

Pros:

• Possibly more Golang:ish
• Makes reading from multiple channels easy
• Fast

Cons:

• Outdated events and messages may be consumed due to the buffering nature of channels. The extent is limited, but not remedied, by the Events channel buffer size (go.events.channel.size).

See examples/consumer_channel_example

Channel Based Producer

Application writes messages to the producer.ProducerChannel. Delivery reports are emitted on the producer.Events or specified private channel.

Pros:

• Go:ish
• Proper channel backpressure if librdkafka internal queue is full.

Cons:

• Double queueing: messages are first queued in the channel (size is configurable) and then inside librdkafka.

See examples/producer_channel_example

Function Based Producer

Application calls producer.Produce() to produce messages. Delivery reports are emitted on the producer.Events or specified private channel.

Pros:

• Go:ish

Cons:

• Produce() is a non-blocking call, if the internal librdkafka queue is full the call will fail.
• Somewhat slower than the channel producer.

See examples/producer_example

Static Builds

NOTE: Requires pkg-config

To link your application statically with librdkafka append -tags static to your application's go build command, e.g.:

$ cd kafkatest/go_verifiable_consumer
$ go build -tags static

This will create a binary with librdkafka statically linked, do note however that any librdkafka dependencies (such as ssl, sasl2, lz4, etc, depending on librdkafka build configuration) will be linked dynamically and thus required on the target system.

To create a completely static binary append -tags static_all instead. This requires all dependencies to be available as static libraries (e.g., libsasl2.a). Static libraries are typically not installed by default but are available in the corresponding ..-dev or ..-devel packages (e.g., libsasl2-dev).

After a succesful static build verify the dependencies by running ldd ./your_program (or otool -L ./your_program on OSX), librdkafka should not be listed.

Tests

See kafka/README

Contributing

Contributions to the code, examples, documentation, et.al, are very much appreciated.

Make your changes, run gofmt, tests, etc, push your branch, create a PR, and sign the CLA.