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Kafka (KRaft)

Since testcontainers-go v0.24.0

Introduction

The Testcontainers module for KRaft: Apache Kafka Without ZooKeeper.

Adding this module to your project dependencies

Please run the following command to add the Kafka module to your Go dependencies:

go get github.com/testcontainers/testcontainers-go/modules/kafka

Usage example

ctx := context.Background()

kafkaContainer, err := kafka.RunContainer(ctx,
    kafka.WithClusterID("test-cluster"),
    testcontainers.WithImage("confluentinc/confluent-local:7.5.0"),
)
if err != nil {
    log.Fatalf("failed to start container: %s", err)
}

// Clean up the container after
defer func() {
    if err := kafkaContainer.Terminate(ctx); err != nil {
        log.Fatalf("failed to terminate container: %s", err)
    }
}()

Module reference

The Kafka module exposes one entrypoint function to create the Kafka container, and this function receives two parameters:

func RunContainer(ctx context.Context, opts ...testcontainers.ContainerCustomizer) (*KafkaContainer, error)
  • context.Context, the Go context.
  • testcontainers.ContainerCustomizer, a variadic argument for passing options.

Container Options

When starting the Kafka container, you can pass options in a variadic way to configure it.

Image

If you need to set a different Kafka Docker image, you can use testcontainers.WithImage with a valid Docker image for Kafka. E.g. testcontainers.WithImage("confluentinc/confluent-local:7.5.0").

Warning

The minimal required version of Kafka for KRaft mode is confluentinc/confluent-local:7.4.0. If you are using an image that is different from the official one, please make sure that it's compatible with KRaft mode, as the module won't check the version for you.

Init script

The Kafka container will be started using a custom shell script:

    starterScriptContent = `#!/bin/bash
source /etc/confluent/docker/bash-config
export KAFKA_ADVERTISED_LISTENERS=PLAINTEXT://%s:%d,BROKER://%s:9092
echo Starting Kafka KRaft mode
sed -i '/KAFKA_ZOOKEEPER_CONNECT/d' /etc/confluent/docker/configure
echo 'kafka-storage format --ignore-formatted -t "$(kafka-storage random-uuid)" -c /etc/kafka/kafka.properties' >> /etc/confluent/docker/configure
echo '' > /etc/confluent/docker/ensure
/etc/confluent/docker/configure
/etc/confluent/docker/launch`

Environment variables

The environment variables that are already set by default are:

"KAFKA_LISTENERS":                                "PLAINTEXT://0.0.0.0:9093,BROKER://0.0.0.0:9092,CONTROLLER://0.0.0.0:9094",
"KAFKA_REST_BOOTSTRAP_SERVERS":                   "PLAINTEXT://0.0.0.0:9093,BROKER://0.0.0.0:9092,CONTROLLER://0.0.0.0:9094",
"KAFKA_LISTENER_SECURITY_PROTOCOL_MAP":           "BROKER:PLAINTEXT,PLAINTEXT:PLAINTEXT,CONTROLLER:PLAINTEXT",
"KAFKA_INTER_BROKER_LISTENER_NAME":               "BROKER",
"KAFKA_BROKER_ID":                                "1",
"KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR":         "1",
"KAFKA_OFFSETS_TOPIC_NUM_PARTITIONS":             "1",
"KAFKA_TRANSACTION_STATE_LOG_REPLICATION_FACTOR": "1",
"KAFKA_TRANSACTION_STATE_LOG_MIN_ISR":            "1",
"KAFKA_LOG_FLUSH_INTERVAL_MESSAGES":              fmt.Sprintf("%d", math.MaxInt),
"KAFKA_GROUP_INITIAL_REBALANCE_DELAY_MS":         "0",
"KAFKA_NODE_ID":                                  "1",
"KAFKA_PROCESS_ROLES":                            "broker,controller",
"KAFKA_CONTROLLER_LISTENER_NAMES":                "CONTROLLER",

Image Substitutions

In more locked down / secured environments, it can be problematic to pull images from Docker Hub and run them without additional precautions.

An image name substitutor converts a Docker image name, as may be specified in code, to an alternative name. This is intended to provide a way to override image names, for example to enforce pulling of images from a private registry.

Testcontainers for Go exposes an interface to perform this operations: ImageSubstitutor, and a No-operation implementation to be used as reference for custom implementations:

// ImageSubstitutor represents a way to substitute container image names
type ImageSubstitutor interface {
    // Description returns the name of the type and a short description of how it modifies the image.
    // Useful to be printed in logs
    Description() string
    Substitute(image string) (string, error)
}

type NoopImageSubstitutor struct{}

// Description returns a description of what is expected from this Substitutor,
// which is used in logs.
func (s NoopImageSubstitutor) Description() string {
    return "NoopImageSubstitutor (noop)"
}

// Substitute returns the original image, without any change
func (s NoopImageSubstitutor) Substitute(image string) (string, error) {
    return image, nil
}

Using the WithImageSubstitutors options, you could define your own substitutions to the container images. E.g. adding a prefix to the images so that they can be pulled from a Docker registry other than Docker Hub. This is the usual mechanism for using Docker image proxies, caches, etc.

WithLogConsumers

  • Not available until the next release of testcontainers-go main

If you need to consume the logs of the container, you can use testcontainers.WithLogConsumers with a valid log consumer. An example of a log consumer is the following:

type TestLogConsumer struct {
    Msgs []string
}

func (g *TestLogConsumer) Accept(l Log) {
    g.Msgs = append(g.Msgs, string(l.Content))
}

Please read the Following Container Logs documentation for more information about creating log consumers.

Wait Strategies

If you need to set a different wait strategy for the container, you can use testcontainers.WithWaitStrategy with a valid wait strategy.

Info

The default deadline for the wait strategy is 60 seconds.

At the same time, it's possible to set a wait strategy and a custom deadline with testcontainers.WithWaitStrategyAndDeadline.

Startup Commands

Testcontainers exposes the WithStartupCommand(e ...Executable) option to run arbitrary commands in the container right after it's started.

Info

To better understand how this feature works, please read the Create containers: Lifecycle Hooks documentation.

It also exports an Executable interface, defining the following methods:

  • AsCommand(), which returns a slice of strings to represent the command and positional arguments to be executed in the container;
  • Options(), which returns the slice of functional options with the Docker's ExecConfigs used to create the command in the container (the working directory, environment variables, user executing the command, etc) and the possible output format (Multiplexed).

You could use this feature to run a custom script, or to run a command that is not supported by the module right after the container is started.

WithNetwork

By default, the container is started in the default Docker network. If you want to use an already existing Docker network you created in your code, you can use the network.WithNetwork(aliases []string, nw *testcontainers.DockerNetwork) option, which receives an alias as parameter and your network, attaching the container to it, and setting the network alias for that network.

In the case you need to retrieve the network name, you can simply read it from the struct's Name field. E.g. nw.Name.

Warning

This option is not checking whether the network exists or not. If you use a network that doesn't exist, the container will start in the default Docker network, as in the default behavior.

WithNewNetwork

If you want to attach your containers to a throw-away network, you can use the network.WithNewNetwork(ctx context.Context, aliases []string, opts ...network.NetworkCustomizer) option, which receives an alias as parameter, creating the new network with a random name, attaching the container to it, and setting the network alias for that network.

In the case you need to retrieve the network name, you can use the Networks(ctx) method of the Container interface, right after it's running, which returns a slice of strings with the names of the networks where the container is attached.

Docker type modifiers

If you need an advanced configuration for the container, you can leverage the following Docker type modifiers:

  • testcontainers.WithConfigModifier
  • testcontainers.WithHostConfigModifier
  • testcontainers.WithEndpointSettingsModifier

Please read the Create containers: Advanced Settings documentation for more information.

Customising the ContainerRequest

This option will merge the customized request into the module's own ContainerRequest.

container, err := RunContainer(ctx,
    /* Other module options */
    testcontainers.CustomizeRequest(testcontainers.GenericContainerRequest{
        ContainerRequest: testcontainers.ContainerRequest{
            Cmd: []string{"-c", "log_statement=all"},
        },
    }),
)

The above example is updating the predefined command of the image, appending them to the module's command.

Info

This can't be used to replace the command, only to append options.

Container Methods

The Kafka container exposes the following methods:

Brokers

The Brokers(ctx) method returns the Kafka brokers as a string slice, containing the host and the random port defined by Kafka's public port (9093/tcp).

brokers, err := kafkaContainer.Brokers(ctx)