Getting Started

Getting started with Kafka

Kafka is available in the Universe and can be installed by using either the web interface or the DC/OS CLI.

Prerequisites

  • Depending on your security mode in Enterprise DC/OS, you may need to provision a service account before installing Kafka. You will need a superuser permission to create the service account. The following is a list of security modes:

    • strict security mode requires a service account.
    • permissive security mode a service account is optional.
    • disabled security mode does not require a service account.
  • Your cluster must have at least three private nodes.

Types of Installation Methods

There are four types of installation methods:

  1. Default installation is the basic installation method. This method is used to install Kafka on a DC/OS cluster using CLI commands.
  2. Minimal installation is used to install Kafka on a local C/OS cluster using dcos-vagrant and is specific for development purposes.
  3. Custom installation is used to install Kafka on DC/OS cluster using a customized JSON file.
  4. Multiple Kafka cluster installation is used to install multiple Kafka clusters using custom configurations.

Default Installation

To start a basic test cluster with three brokers, run the following command on the DC/OS CLI. Enterprise DC/OS users must follow additional instructions. More information about installing Kafka on Enterprise DC/OS.

$ dcos package install kafka

This command creates a new Kafka cluster with the default name kafka. Two clusters cannot share the same name, so installing additional clusters beyond the default cluster requires customizing the name at install time for each additional instance.

All dcos kafka CLI commands have a --name argument allowing the user to specify which Kafka instance to query. If you do not specify a service name, the CLI assumes the default value, kafka. The default value for --name can be customized via the DC/OS CLI configuration:

$ dcos kafka --name=<kafka-dev> <cmd>

NOTE: Alternatively, you can install Kafka from the DC/OS web interface. If you install Kafka from the web interface, you must install the Kafka DC/OS CLI subcommands separately.

Enter the following command from the DC/OS CLI:

$ dcos package install kafka --cli

Minimal Installation

For development purposes, you can use dcos-vagrant to install Kafka on a local DC/OS cluster.

To start a minimal cluster with a single broker, create a JSON options file named sample-kafka-minimal.json:

{
    "brokers": {
        "count": 1,
        "mem": 512,
        "disk": 1000
    }
}

The command below creates a cluster using sample-kafka-minimal.json:

$ dcos package install --options=sample-kafka-minimal.json kafka

Custom Installation

Customize the defaults by creating a JSON file; then pass it to dcos package install using the --options parameter.

Sample JSON options file named sample-kafka-custom.json:

{
    "service": {
        "name": "sample-kafka-custom",
        "placement_strategy": "NODE"
    },
    "brokers": {
        "count": 10,
        "kill_grace_period": 30
    },
    "kafka": {
        "delete_topic_enable": true,
        "log_retention_hours": 128
    }
}

The command below creates a cluster using sample-kafka.json:

$ dcos package install --options=sample-kafka-custom.json kafka

IMPORTANT: It is highly recommended to store your custom configuration in source control.

See Configuration Options for a list of fields that can be customized via an options JSON file when the Kafka cluster is created.

Multiple Kafka cluster installation

Installing multiple Kafka clusters is identical to installing Kafka clusters with custom configurations as described above. The only requirement on the operator is that a unique name is specified for each installation.

See the example below:

$ cat kafka1.json
{
    "service": {
        "name": "kafka1"
    }
}

$ dcos package install kafka --options=kafka1.json

Changing Configuration at Runtime

You can customize your cluster in-place after it is up and running.

The Kafka scheduler runs as a Marathon process and can be reconfigured by changing values from the DC/OS web interface.

Use the following steps to change configurations at runtime.

  1. Go to the Services tab of the DC/OS web interface.
  2. Select the name of the Kafka service to be updated.
  3. Within the Kafka instance details view, select the menu in the upper right, then choose Edit.
  4. In the dialog that appears, select the Environment tab and update any fields to their desired values. For example, to increase the number of Brokers, edit the value for BROKER_COUNT. Do not edit the value for FRAMEWORK_NAME or BROKER_DISK.
  5. Choose a DEPLOY_STRATEGY: serial, serial-canary, parallel-canary, or parallel. See the SDK Developer guide for more information on deployment plan strategies.
  6. Select REVIEW & RUN to apply any changes and cleanly reload the Kafka scheduler. The Kafka cluster itself will persist across the change.

Configuration Update REST API

Make the REST request below to view the current deployment plan. See the REST API Authentication part of the REST API Reference topic for information on how this request must be authenticated.

$ curl -H "Authorization: token=$auth_token" "<dcos_url>/service/kafka/v1/plan"

{
    "phases": [
        {
            "id": "b6180a4e-b25f-4307-8855-0b37d671fd46",
            "name": "Deployment",
            "steps": [
                {
                    "id": "258f19a4-d6bc-4ff1-8685-f314924884a1",
                    "status": "COMPLETE",
                    "name": "kafka-0:[broker]",
                    "message": "com.mesosphere.sdk.scheduler.plan.DeploymentStep: 'kafka-0:[broker] [258f19a4-d6bc-4ff1-8685-f314924884a1]' has status: 'COMPLETE'."
                },
                {
                    "id": "e59fb2a9-22e2-4900-89e3-bda24041639f",
                    "status": "COMPLETE",
                    "name": "kafka-1:[broker]",
                    "message": "com.mesosphere.sdk.scheduler.plan.DeploymentStep: 'kafka-1:[broker] [e59fb2a9-22e2-4900-89e3-bda24041639f]' has status: 'COMPLETE'."
                },
                {
                    "id": "0b5a5048-fd3a-4b2c-a9b5-746045176d29",
                    "status": "COMPLETE",
                    "name": "kafka-2:[broker]",
                    "message": "com.mesosphere.sdk.scheduler.plan.DeploymentStep: 'kafka-2:[broker] [0b5a5048-fd3a-4b2c-a9b5-746045176d29]' has status: 'COMPLETE'."
                }
            ],
            "status": "COMPLETE"
        }
    ],
    "errors": [],
    "status": "COMPLETE"
}

NOTE: After a configuration update, you may see an error from Mesos-DNS; this will go away 10 seconds after the update.

Enter the continue command to execute the first step:

$ curl -X PUT -H "Authorization: token=$auth_token" "<dcos_url>/service/kafka/v1/plan?cmd=continue"
PUT <dcos_url>/service/kafka/v1/continue HTTP/1.1

{
    "Result": "Received cmd: continue"
}

After you execute the continue operation, the plan will look like the following code block:

$ curl -H "Authorization: token=$auth_token" "<dcos_url>/service/kafka/v1/plan"
GET <dcos_url>/service/kafka/v1/plan HTTP/1.1

{
    "phases": [
    {
        "id": "9f8927de-d0df-4f72-bd0d-55e3f2c3ab21",
        "name": "Reconciliation",
        "steps": [
        {
            "id": "2d137273-249b-455e-a65c-3c83228890b3",
            "status": "COMPLETE",
            "name": "Reconciliation",
            "message": "Reconciliation complete"
        }
        ],
        "status": "COMPLETE"
    },
    {
        "id": "a7742963-f7e1-4640-8bd0-2fb28dc04045",
        "name": "Update to: 6092e4ec-8ffb-49eb-807b-877a85ef8859",
        "steps": [
        {
            "id": "b4453fb0-b4cc-4996-a05c-762673f75e6d",
            "status": "IN_PROGRESS",
            "name": "broker-0",
            "message": "Broker-0 is IN_PROGRESS"
        },
        {
            "id": "b8a8de9f-8758-4d0f-b785-0a38751a2c94",
            "status": "WAITING",
            "name": "broker-1",
            "message": "Broker-1 is WAITING"
        },
        {
            "id": "49e85522-1bcf-4edb-9456-712e8a537dbc",
            "status": "PENDING",
            "name": "broker-2",
            "message": "Broker-2 is PENDING"
        }
        ],
        "status": "IN_PROGRESS"
    }
    ],
    "errors": [],
    "status": "IN_PROGRESS"
}

If you enter continue a second time, the rest of the plan will be executed without further interruption. If you want to interrupt a configuration update that is in progress, enter the interrupt command:

$ curl -X PUT -H "Authorization: token=$auth_token"  "<dcos_url>/service/kafka/v1/plan?cmd=interrupt"
PUT <dcos_url>/service/kafka/v1/interrupt HTTP/1.1

{
    "Result": "Received cmd: interrupt"
}

WARNING: The interrupt command cannot terminate a step that is InProgress, but it will stop the change on the subsequent steps.

Configuration Options

The following describes the most commonly used features of the Kafka service and how to configure them via the DC/OS CLI and from the DC/OS web interface. View the default config.json in DC/OS Universe to see all possible configuration options.

Service Name

The name of this Kafka instance in DC/OS. This is an option that cannot be changed once the Kafka cluster is started: it can only be configured via the DC/OS CLI --options flag when the Kafka instance is created.

  • In DC/OS CLI options.json: name: string (default: kafka)
  • DC/OS web interface: The service name cannot be changed after the cluster has started.

Kill Grace Period

The kill grace period is the number of seconds each broker has to cleanly shut down in response to SIGTERM. If a broker exceeds this time, it will be killed. Use the brokers.kill_grace_period configuration option to set a kill grace period.

The graceful shutdown feature is especially important for large-scale deployments. Use the graceful shutdown configuraiton option to provide the broker sufficient time during shutdown. This ensure that all in-memory data is flushed to disk and all state is replicated. When a broker has sufficient time to shut down, the subsequent restart will be nearly as fast as the first startup. This is a large contributor to the Kafka service’s high availability.

You can observe the graceful shutdown feature via the following log entries:

  1. The task launch log line contains kill_policy { grace_period { nanoseconds: 30000000000 } }.
  2. The task graceful shutdown log line contains SIGTERM as well as the grace time granted.
  3. The underlying Kafka logging of shutdown operations includes a stream of subsystem shutdowns prior to the overarching system shutdown indicated by the entry [Kafka Server 1], shut down completed (kafka.server.KafkaServer).
  4. The presence (or not) of a SIGKILL log line indicating that the underlying Kafka broker did not shutdown cleanly within the allotted grace period.
  5. The task status update marked by TASK_KILLED, indicating the end of the shutdown activity.

Broker Count

Configure the number of brokers running in a given Kafka cluster. The default count at installation is three brokers. This number may be increased, but not decreased, after installation.

  • In DC/OS CLI options.json: broker-count: integer (default: 3)
  • DC/OS web interface: BROKER_COUNT: integer

Broker Port

Configure the port number that the brokers listen on. If the brokers.port is set to a particular value, this will be the port used by all brokers. Note that this requires that placement-strategy be set to NODE to take effect, since having every broker listening on the same port requires that they be placed on different hosts. By default the port is set to 0, indicating that each Broker will have a random port from the port range offered by the Mesos Agent between 1025 and 32000

  • In DC/OS CLI options.json: brokers.port: integer (default: 0)
  • DC/OS web interface: Port: integer

Apache Kafka brokers also get assigned a VIP hostname for load-balancing purposes. This VIP is broker.<SERVICE_NAME>.l4lb.thisdcos.directory:9092, where <SERVICE_NAME> is the service name you have provided when creating the Kafka cluster. By default, the <SERVICE_NAME> is kafka therefore, by default, the VIP is broker.kafka.l4lb.thisdcos.directory:9092.

When security.transport_encryption.enabled is true the VIP hostname uses the port 9093

Configure Broker Placement Strategy

ANY allows brokers to be placed on any node with sufficient resources, while NODE ensures that all brokers within a given Kafka cluster are never colocated on the same node. This is an option that cannot be changed once the Kafka cluster is started: it can only be configured via the DC/OS CLI --options flag when the Kafka instance is created.

  • In DC/OS CLI options.json: placement-strategy: ANY or NODE (default: ANY)
  • DC/OS web interface: PLACEMENT_STRATEGY: ANY or NODE

Configure Kafka Broker Properties

Kafka Brokers are configured through settings in a server.properties file deployed with each Broker. The settings here can be specified at installation time or during a post-deployment configuration update. They are set in the DC/OS Universe’s config.json as options such as:

    "log_retention_hours": {
        "title": "log.retention.hours",
        "description": "Override log.retention.hours: The number of hours to keep a log file before deleting it (in hours), tertiary to log.retention.ms property",
        "type": "integer",
        "default": 168
    },

The defaults can be overridden at install time by specifying an options.json file with a format like this:

    {
        "kafka": {
            "log_retention_hours": 100
        }
    }

These same values are also represented as environment variables for the scheduler in the form KAFKA_OVERRIDE_LOG_RETENTION_HOURS and may be modified through the DC/OS web interface and deployed during a rolling upgrade as described here.

Disk Type

The type of disks that can be used for storing broker data are: ROOT (default) and MOUNT. The type of disk may only be specified at install time.

  • ROOT: Broker data is stored on the same volume as the agent work directory. Broker tasks will use the configured amount of disk space.
  • MOUNT: Broker data will be stored on a dedicated volume attached to the agent. Dedicated MOUNT volumes have performance advantages and a disk error on these MOUNT volumes will be correctly reported to Kafka.

Configure Kafka service to use dedicated disk volumes:

  • DC/OS cli options.json:
    {
        "brokers": {
            "disk_type": "MOUNT"
        }
    }
  • DC/OS web interface: Set the environment variable DISK_TYPE: MOUNT

When configured to MOUNT disk type, the scheduler selects a disk on an agent whose capacity is equal to or greater than the configured disk value.

JVM Heap Size

Kafka service allows configuration of JVM Heap Size for the broker JVM process. Use the following configuration options:

    {
        "brokers": {
            "heap": {
                "size": 2000
            }
        }
    }
  • DC/OS web interface: Set the environment variable BROKER_HEAP_MB: 2000

NOTE: The total memory allocated for the Mesos task is specified by the BROKER_MEM configuration parameter. The value for BROKER_HEAP_MB should not be greater than BROKER_MEM value. Also, if BROKER_MEM is greater than BROKER_HEAP_MB then the Linux operating system will use BROKER_MEM - BROKER_HEAP_MB for [PageCache](https://en.wikipedia.org/wiki/Page_cache).

Alternate ZooKeeper

By default the Kafka framework uses the ZooKeeper ensemble made available on the Mesos masters of a DC/OS cluster. You can configure an alternate ZooKeeper at install time.

Use the following configuration options:

  • DC/OS CLI options.json:
    {
        "kafka": {
            "kafka_zookeeper_uri": "zookeeper.marathon.autoip.dcos.thisdcos.directory:2181"
        }
    }

This configuration option cannot be changed after installation.

Recovery and Health Checks

You can enable automated replacement of brokers and configure the circumstances under which they are replaced.

Enable Broker Replacement

To enable automated replacement using the following options:

  • DC/OS CLI options.json:
    {
        "enable_replacement":{
            "description":"Enable automated replacement of Brokers. WARNING: May cause data loss. See documentation.",
            "type":"boolean",
            "default":false
        }
    }
  • DC/OS web interface: Set the environment variable ENABLE_REPLACEMENT: true to enable replacement.

WARNING: text

**Warning:** The replacement mechanism is not aware of whether the broker has been destructively replaced with the latest copy of data. You may lose data depending on your replication policy, the degree, and duration of the permanent failures.

The following configuration options control the circumstances under which a broker is replaced.

Minumum Grace Period

Configure the minimum amount of time before a broker should be replaced:

  • DC/OS CLI options.json:
    {
        "recover_in_place_grace_period_secs":{
            "description":"The minimum amount of time (in minutes) which must pass before a Broker may be destructively replaced.",
            "type":"number",
            "default":1200
        }
    }
  • DC/OS web interface: Set the environment variable RECOVERY_GRACE_PERIOD_SEC: 1200

Minumum Delay Between Replacements

Configure the minimum amount of time between broker replacements.

    {
        "min_delay_between_recovers_secs":{
            "description":"The minimum amount of time (in seconds) which must pass between destructive replacements of Brokers.",
            "type":"number",
            "default":600
        }
    }
  • DC/OS web interface: Set the environment variable REPLACE_DELAY_SEC: 600

The following configurations control the health checks that determine when a broker has failed:

Enable Health Check

Enable health checks on brokers:

    {
        "enable_health_check":{
            "description":"Enable automated detection of Broker failures which did not result in a Broker process exit.",
            "type":"boolean",
            "default":true
        }
    }
  • DC/OS web interface: Set the environment variable ENABLE_BROKER_HEALTH_CHECK: true

Health Check Delay

Set the amount of time before the health check begins:

    {
        "health_check_delay_sec":{
            "description":"The period of time (in seconds) waited before the health-check begins execution.",
            "type":"number",
            "default":15
        }
    }
  • DC/OS web interface: Set the environment variable BROKER_HEALTH_CHECK_DELAY_SEC: 15

Health Check Interval

Set the interval between health checks:

    {
        "health_check_interval_sec":{
            "description":"The period of time (in seconds) between health-check executions.",
            "type":"number",
            "default":10
        }
    }
  • DC/OS web interface: Set the environment variable BROKER_HEALTH_CHECK_INTERVAL_SEC: 10

Health Check Timeout

Set the time a health check can take to complete before it is considered a failed check:

    {
        "health_check_timeout_sec":{
            "description":"The duration (in seconds) allowed for a health-check to complete before it is considered a failure.",
            "type":"number",
            "default":20
        }
    }
  • DC/OS web interface: Set the environment variable BROKER_HEALTH_CHECK_TIMEOUT_SEC: 20

Health Check Grace Period

Set the amount of time after the delay before health check failures count toward the maximum number of consecutive failures:

    {
        "health_check_grace_period_sec":{
            "description":"The period of time after the delay (in seconds) before health-check failures count towards the maximum consecutive failures.",
            "type":"number",
            "default":10
        }
    }
  • DC/OS web interface: Set the environment variable BROKER_HEALTH_CHECK_GRACE_SEC: 10

Maximum Consecutive Health Check Failures

    {
        "health_check_max_consecutive_failures":{
            "description":"The number of consecutive failures which cause a Broker process to exit.",
            "type":"number",
            "default":3
        }
    }
  • DC/OS web interface: Set the environment variable BROKER_HEALTH_CHECK_MAX_FAILURES: 3