kafkactl

A command-line interface for interaction with Apache Kafka

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Features

• command auto-completion for bash, zsh, fish shell including dynamic completion for e.g. topics or consumer groups.
• support for avro schemas
• Configuration of different contexts
• directly access kafka clusters inside your kubernetes cluster

Installation

You can install the pre-compiled binary or compile from source.

Install the pre-compiled binary

snapcraft:

snap install kafkactl

homebrew:

# install tap repostory once
brew tap deviceinsight/packages
# install kafkactl
brew install deviceinsight/packages/kafkactl
# upgrade kafkactl
brew upgrade deviceinsight/packages/kafkactl

deb/rpm:

Download the .deb or .rpm from the releases page and install with dpkg -i and rpm -i respectively.

yay (AUR)

There's a kafkactl AUR package available for Arch. Install it with your AUR helper of choice (e.g. yay):

yay -S kafkactl

manually:

Download the pre-compiled binaries from the releases page and copy to the desired location.

Compiling from source

go get -u github.com/deviceinsight/kafkactl

NOTE: make sure that kafkactl is on PATH otherwise auto-completion won't work.

Configuration

If no config file is found, a default config is generated in $HOME/.config/kafkactl/config.yml. This configuration is suitable to get started with a single node cluster on a local machine.

Create a config file

Create $HOME/.config/kafkactl/config.yml with a definition of contexts that should be available

contexts:
  default:
    brokers:
    - localhost:9092
  remote-cluster:
    brokers:
    - remote-cluster001:9092
    - remote-cluster002:9092
    - remote-cluster003:9092

    # optional: tls config
    tls:
      enabled: true
      ca: my-ca
      cert: my-cert
      certKey: my-key
      # set insecure to true to ignore all tls verification (defaults to false)
      insecure: false

    # optional: sasl support
    sasl:
      enabled: true
      username: admin
      password: admin
  
    # optional: access clusters running kubernetes
    kubernetes:
      enabled: false
      binary: kubectl #optional
      kubeConfig: ~/.kube/config #optional
      kubeContext: my-cluster
      namespace: my-namespace

    # optional: clientID config (defaults to kafkactl-{username})
    clientID: my-client-id
    
    # optional: kafkaVersion (defaults to 2.0.0)
    kafkaVersion: 1.1.1

    # optional: avro schema registry
    avro:
      schemaRegistry: localhost:8081
    
    # optional: changes the default partitioner
    defaultPartitioner: "hash"


current-context: default

The config file location is resolved by

• checking for a provided commandline argument: --config-file=$PATH_TO_CONFIG
• or by evaluating the environment variable: export KAFKA_CTL_CONFIG=$PATH_TO_CONFIG
• or as default the config file is looked up from one of the following locations:
  • $HOME/.config/kafkactl/config.yml
  • $HOME/.kafkactl/config.yml
  • $SNAP_DATA/kafkactl/config.yml
  • /etc/kafkactl/config.yml

Auto completion

bash

NOTE: if you installed via snap, bash completion should work automatically.

source <(kafkactl completion bash)

To load completions for each session, execute once: Linux:

kafkactl completion bash > /etc/bash_completion.d/kafkactl

MacOS:

kafkactl completion bash > /usr/local/etc/bash_completion.d/kafkactl

zsh

source <(kafkactl completion zsh)

To load completions for each session, execute once:

kafkactl completion zsh > "${fpath[1]}/_kafkactl"

Fish

kafkactl completion fish | source

To load completions for each session, execute once:

kafkactl completion fish > ~/.config/fish/completions/kafkactl.fish

Running in docker

Assuming your Kafka broker is accessible as kafka:9092, you can list topics by running:

docker run --env BROKERS=kafka:9092 deviceinsight/kafkactl:latest get topics

If a more elaborate config is needed, you can mount it as a volume:

docker run -v /absolute/path/to/config.yml:/etc/kafkactl/config.yml deviceinsight/kafkactl get topics

Configuration via environment variables

Every key in the config.yml can be overwritten via environment variables. The corresponding environment variable for a key can be found by applying the following rules:

1. replace . by _
2. replace - by _
3. write the key name in ALL CAPS

e.g. the key contexts.default.tls.certKey has the corresponding environment variable CONTEXTS_DEFAULT_TLS_CERTKEY.

If environment variables for the default context should be set, the prefix CONTEXTS_DEFAULT_ can be omitted. So, instead of CONTEXTS_DEFAULT_TLS_CERTKEY one can also set TLS_CERTKEY. See root_test.go for more examples.

Running in Kubernetes

If your kafka cluster is not directly accessible from your machine, but it is accessible from a kubernetes cluster which in turn is accessible via kubectl from your machine you can configure kubernetes support:

contexts:
  kafka-cluster:
    kubernetes:
      enabled: true
      kubeContext: k8s-cluster
      namespace: k8s-namespace

Instead of directly talking to kafka brokers a kafkactl docker image is deployed as a pod into the kubernetes cluster, and the defined namespace. Standard-Input and Standard-Output are then wired between the pod and your shell running kafkactl.

There are two options:

1. You can run kafkactl attach with your kubernetes cluster configured. This will use kubectl run to create a pod in the configured kubeContext/namespace which runs an image of kafkactl and gives you a bash into the container. Standard-in is piped to the pod and standard-out, standard-err directly to your shell. You even get auto-completion.

2. You can run any other kafkactl command with your kubernetes cluster configured. Instead of directly querying the cluster a pod is deployed, and input/output are wired between pod and your shell.

NOTE: The first option takes a bit longer to start up since an Ubuntu based docker image is used in order to have a bash available. The second option uses a docker image build from scratch and should therefore be quicker. Which option is more suitable, will depend on your use-case.

Command documentation

The documentation for all available commands can be found here:

Examples

Consuming messages

Consuming messages from a topic can be done with:

kafkactl consume my-topic

In order to consume starting from the oldest offset use:

kafkactl consume my-topic --from-beginning

The following example prints message key and timestamp as well as partition and offset in yaml format:

kafkactl consume my-topic --print-keys --print-timestamps -o yaml

Headers of kafka messages can be printed with the parameter --print-headers e.g.:

kafkactl consume my-topic --print-headers -o yaml

If one is only interested in the last n messages this can be achieved by --tail e.g.:

kafkactl consume my-topic --tail=5

The consumer can be stopped when the latest offset is reached using --exit parameter e.g.:

kafkactl consume my-topic --from-beginning --exit

The following example prints keys in hex and values in base64:

kafkactl consume my-topic --print-keys --key-encoding=hex --value-encoding=base64

Producing messages

Producing messages can be done in multiple ways. If we want to produce a message with key='my-key', value='my-value' to the topic my-topic this can be achieved with one of the following commands:

echo "my-key#my-value" | kafkactl produce my-topic --separator=#
echo "my-value" | kafkactl produce my-topic --key=my-key
kafkactl produce my-topic --key=my-key --value=my-value

If we have a file containing messages where each line contains key and value separated by #, the file can be used as input to produce messages to topic my-topic:

cat myfile | kafkactl produce my-topic --separator=#

The same can be accomplished without piping the file to stdin with the --file parameter:

kafkactl produce my-topic --separator=# --file=myfile

If the messages in the input file need to be split by a different delimiter than \n a custom line separator can be provided:

kafkactl produce my-topic --separator=# --lineSeparator=|| --file=myfile

NOTE: if the file was generated with kafkactl consume --print-keys --print-timestamps my-topic the produce command is able to detect the message timestamp in the input and will ignore it.

the number of messages produced per second can be controlled with the --rate parameter:

cat myfile | kafkactl produce my-topic --separator=# --rate=200

It is also possible to specify the partition to insert the message:

kafkactl produce my-topic --key=my-key --value=my-value --partition=2

Additionally, a different partitioning scheme can be used. When a key is provided the default partitioner uses the hash of the key to assign a partition. So the same key will end up in the same partition:

# the following 3 messages will all be inserted to the same partition
kafkactl produce my-topic --key=my-key --value=my-value
kafkactl produce my-topic --key=my-key --value=my-value
kafkactl produce my-topic --key=my-key --value=my-value

# the following 3 messages will probably be inserted to different partitions
kafkactl produce my-topic --key=my-key --value=my-value --partitioner=random
kafkactl produce my-topic --key=my-key --value=my-value --partitioner=random
kafkactl produce my-topic --key=my-key --value=my-value --partitioner=random

Message headers can also be written:

kafkactl produce my-topic --key=my-key --value=my-value --header key1:value1 --header key2:value\:2

The following example writes the key from base64 and value from hex:

kafkactl produce my-topic --key=dGVzdC1rZXk= --key-encoding=base64 --value=0000000000000000 --value-encoding=hex

Avro support

In order to enable avro support you just have to add the schema registry to your configuration:

contexts:
  localhost:
    avro:
      schemaRegistry: localhost:8081

Producing to an avro topic

kafkactl will lookup the topic in the schema registry in order to determine if key or value needs to be avro encoded. If producing with the latest schemaVersion is sufficient, no additional configuration is needed an kafkactl handles this automatically.

If however one needs to produce an older schemaVersion this can be achieved by providing the parameters keySchemaVersion, valueSchemaVersion.

Example

# create a topic
kafkactl create topic avro_topic
# add a schema for the topic value
curl -X POST -H "Content-Type: application/vnd.schemaregistry.v1+json" \
--data '{"schema": "{\"type\": \"record\", \"name\": \"LongList\", \"fields\" : [{\"name\": \"next\", \"type\": [\"null\", \"LongList\"], \"default\": null}]}"}' \
http://localhost:8081/subjects/avro_topic-value/versions
# produce a message
kafkactl produce avro_topic --value {\"next\":{\"LongList\":{}}}
# consume the message
kafkactl consume avro_topic --from-beginning --print-schema -o yaml

Consuming from an avro topic

As for producing kafkactl will also lookup the topic in the schema registry to determine if key or value needs to be decoded with an avro schema.

The consume command handles this automatically and no configuration is needed.

An additional parameter print-schema can be provided to display the schema used for decoding.

Altering topics

Using the alter topic command allows you to change the partition count and topic-level configurations of an existing topic.

The partition count can be increased with:

kafkactl alter topic my-topic --partitions 32

The topic configs can be edited by supplying key value pairs as follows:

kafkactl alter topic my-topic --config retention.ms=3600 --config cleanup.policy=compact

Consumer groups

In order to get a list of consumer groups the get consumer-groups command can be used:

# all available consumer groups
kafkactl get consumer-groups 
# only consumer groups for a single topic
kafkactl get consumer-groups --topic my-topic
# using command alias
kafkactl get cg

To get detailed information about the consumer group use describe consumer-group. If the parameter --partitions is provided details will be printed for each partition otherwise the partitions are aggregated to the clients.

# describe a consumer group
kafkactl describe consumer-group my-group 
# show partition details only for partitions with lag
kafkactl describe consumer-group my-group --only-with-lag
# show details only for a single topic
kafkactl describe consumer-group my-group --topic my-topic
# using command alias
kafkactl describe cg my-group

Reset consumer group offsets

in order to ensure the reset does what it is expected, per default only the results are printed without actually executing it. Use the additional parameter --execute to perform the reset.

# reset offset of for all partitions to oldest offset
kafkactl reset offset my-group --topic my-topic --oldest
# reset offset of for all partitions to newest offset
kafkactl reset offset my-group --topic my-topic --newest
# reset offset for a single partition to specific offset
kafkactl reset offset my-group --topic my-topic --partition 5 --offset 100