kafka-docker

Dockerfile for Apache Kafka

The image is available directly from Docker Hub

EdgeOne notes

At bootup the entrypoint queries zookeeper and finds a free brokerid starting by 1. The entrypoint will automatically detect the previously used broker ID stored on the persistent volume. (todo: limit max number of brokers to avoid random high broker IDs or long boot loop)

Managing persistent storage in a multi-instance cluster environment: The default configuration ships with just one instance of kafka in mind. However, the container is setup (depending on the persistent storage used - writeonce or writemany) to handle scaling and can be setup in two ways:

1. Copy the deployment manifest and add as many instances of kafka as desired with unique broker-ids and servicenames
2. Use a shared blockdevice and filesystem for the storage device that supports Write-Many-Mode https://kubernetes.io/docs/concepts/storage/persistent-volumes/ leave the brokerid empty, by default the system reverts to BROKER_ID_COMMAND = /app/getfreebrokerid.sh (this is currently untested and would require to change the logic how the logs are stored on the volume)

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Announcements

• 04-Jun-2019 - Update base image to openjdk 212 (Release notes. Please force pull to get these latest updates - including security patches etc.

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Pre-Requisites

• install docker-compose https://docs.docker.com/compose/install/
• modify the KAFKA_ADVERTISED_HOST_NAME in docker-compose.yml to match your docker host IP (Note: Do not use localhost or 127.0.0.1 as the host ip if you want to run multiple brokers.)
• if you want to customize any Kafka parameters, simply add them as environment variables in docker-compose.yml, e.g. in order to increase the message.max.bytes parameter set the environment to KAFKA_MESSAGE_MAX_BYTES: 2000000. To turn off automatic topic creation set KAFKA_AUTO_CREATE_TOPICS_ENABLE: 'false'
• Kafka's log4j usage can be customized by adding environment variables prefixed with LOG4J_. These will be mapped to log4j.properties. For example: LOG4J_LOGGER_KAFKA_AUTHORIZER_LOGGER=DEBUG, authorizerAppender

NOTE: There are several 'gotchas' with configuring networking. If you are not sure about what the requirements are, please check out the Connectivity Guide in the Wiki

Usage

Start a cluster:

• docker-compose up -d

Add more brokers:

• docker-compose scale kafka=3

Destroy a cluster:

• docker-compose stop

Note

The default docker-compose.yml should be seen as a starting point. By default each broker will get a new port number and broker id on restart. Depending on your use case this might not be desirable. If you need to use specific ports and broker ids, modify the docker-compose configuration accordingly, e.g. docker-compose-single-broker.yml:

• docker-compose -f docker-compose-single-broker.yml up

Broker IDs

You can configure the broker id in different ways

1. explicitly, using KAFKA_BROKER_ID
2. via a command, using BROKER_ID_COMMAND, e.g. BROKER_ID_COMMAND: "hostname | awk -F'-' '{print $$2}'"

If you don't specify a broker id in your docker-compose file, it will automatically be generated (see https://issues.apache.org/jira/browse/KAFKA-1070. This allows scaling up and down. In this case it is recommended to use the --no-recreate option of docker-compose to ensure that containers are not re-created and thus keep their names and ids.

Automatically create topics

If you want to have kafka-docker automatically create topics in Kafka during creation, a KAFKA_CREATE_TOPICS environment variable can be added in docker-compose.yml.

Here is an example snippet from docker-compose.yml:

    environment:
      KAFKA_CREATE_TOPICS: "Topic1:1:3,Topic2:1:1:compact"

Topic 1 will have 1 partition and 3 replicas, Topic 2 will have 1 partition, 1 replica and a cleanup.policy set to compact. Also, see FAQ: Topic compaction does not work

If you wish to use multi-line YAML or some other delimiter between your topic definitions, override the default , separator by specifying the KAFKA_CREATE_TOPICS_SEPARATOR environment variable.

For example, KAFKA_CREATE_TOPICS_SEPARATOR: "$$'\n'" would use a newline to split the topic definitions. Syntax has to follow docker-compose escaping rules, and ANSI-C quoting.

Advertised hostname

You can configure the advertised hostname in different ways

1. explicitly, using KAFKA_ADVERTISED_HOST_NAME
2. via a command, using HOSTNAME_COMMAND, e.g. HOSTNAME_COMMAND: "route -n | awk '/UG[ \t]/{print $$2}'"

When using commands, make sure you review the "Variable Substitution" section in https://docs.docker.com/compose/compose-file/

If KAFKA_ADVERTISED_HOST_NAME is specified, it takes precedence over HOSTNAME_COMMAND

For AWS deployment, you can use the Metadata service to get the container host's IP:

HOSTNAME_COMMAND=wget -t3 -T2 -qO-  http://169.254.169.254/latest/meta-data/local-ipv4

Reference: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-metadata.html

Injecting HOSTNAME_COMMAND into configuration

If you require the value of HOSTNAME_COMMAND in any of your other KAFKA_XXX variables, use the _{HOSTNAME_COMMAND} string in your variable value, i.e.

KAFKA_ADVERTISED_LISTENERS=SSL://_{HOSTNAME_COMMAND}:9093,PLAINTEXT://9092

Advertised port

If the required advertised port is not static, it may be necessary to determine this programatically. This can be done with the PORT_COMMAND environment variable.

PORT_COMMAND: "docker port $$(hostname) 9092/tcp | cut -d: -f2"

This can be then interpolated in any other KAFKA_XXX config using the _{PORT_COMMAND} string, i.e.

KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://1.2.3.4:_{PORT_COMMAND}

Listener Configuration

It may be useful to have the Kafka Documentation open, to understand the various broker listener configuration options.

Since 0.9.0, Kafka has supported multiple listener configurations for brokers to help support different protocols and discriminate between internal and external traffic. Later versions of Kafka have deprecated advertised.host.name and advertised.port.

NOTE: advertised.host.name and advertised.port still work as expected, but should not be used if configuring the listeners.

Example

The example environment below:

HOSTNAME_COMMAND: curl http://169.254.169.254/latest/meta-data/public-hostname
KAFKA_ADVERTISED_LISTENERS: INSIDE://:9092,OUTSIDE://_{HOSTNAME_COMMAND}:9094
KAFKA_LISTENERS: INSIDE://:9092,OUTSIDE://:9094
KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: INSIDE:PLAINTEXT,OUTSIDE:PLAINTEXT
KAFKA_INTER_BROKER_LISTENER_NAME: INSIDE

Will result in the following broker config:

advertised.listeners = OUTSIDE://ec2-xx-xx-xxx-xx.us-west-2.compute.amazonaws.com:9094,INSIDE://:9092
listeners = OUTSIDE://:9094,INSIDE://:9092
inter.broker.listener.name = INSIDE

Rules

• No listeners may share a port number.
• An advertised.listener must be present by protocol name and port number in the list of listeners.

Broker Rack

You can configure the broker rack affinity in different ways

1. explicitly, using KAFKA_BROKER_RACK
2. via a command, using RACK_COMMAND, e.g. RACK_COMMAND: "curl http://169.254.169.254/latest/meta-data/placement/availability-zone"

In the above example the AWS metadata service is used to put the instance's availability zone in the broker.rack property.

JMX

For monitoring purposes you may wish to configure JMX. Additional to the standard JMX parameters, problems could arise from the underlying RMI protocol used to connect

• java.rmi.server.hostname - interface to bind listening port
• com.sun.management.jmxremote.rmi.port - The port to service RMI requests

For example, to connect to a kafka running locally (assumes exposing port 1099)

  KAFKA_JMX_OPTS: "-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -Djava.rmi.server.hostname=127.0.0.1 -Dcom.sun.management.jmxremote.rmi.port=1099"
  JMX_PORT: 1099

Jconsole can now connect at jconsole 192.168.99.100:1099

Docker Swarm Mode

The listener configuration above is necessary when deploying Kafka in a Docker Swarm using an overlay network. By separating OUTSIDE and INSIDE listeners, a host can communicate with clients outside the overlay network while still benefiting from it from within the swarm.

In addition to the multiple-listener configuration, additional best practices for operating Kafka in a Docker Swarm include:

• Use "deploy: global" in a compose file to launch one and only one Kafka broker per swarm node.
• Use compose file version '3.2' (minimum Docker version 16.04) and the "long" port definition with the port in "host" mode instead of the default "ingress" load-balanced port binding. This ensures that outside requests are always routed to the correct broker. For example:

ports:
   - target: 9094
     published: 9094
     protocol: tcp
     mode: host

Older compose files using the short-version of port mapping may encounter Kafka client issues if their connection to individual brokers cannot be guaranteed.

See the included sample compose file docker-compose-swarm.yml

Release process

See the wiki for information on adding or updating versions to release to Dockerhub.

Tutorial

http://wurstmeister.github.io/kafka-docker/