Kafdrop – Kafka Web UI

Kafdrop 3 is a web UI for browsing Kafka topics and consumer groups. The tool displays information such as brokers, topics, partitions, consumers, and lets you view messages.

This project is a reboot of Kafdrop 2.x, dragged kicking and screaming into the world of JDK 11+, Kafka 2.x, Helm and Kubernetes. It's a lightweight application that runs on Spring Boot and is dead-easy to configure, supporting SASL and TLS-secured brokers.

Requirements

• Java 11 or newer
• Kafka (version 0.10.0 or newer)

Optional, additional integration:

• Schema Registry

Getting Started

You can run the Kafdrop JAR directly, via Docker, or in Kubernetes.

Running from JAR

java --add-opens=java.base/sun.nio.ch=ALL-UNNAMED \
    -jar target/kafdrop-<version>.jar \
    --kafka.brokerConnect=<host:port,host:port>,...

If unspecified, kafka.brokerConnect defaults to localhost:9092.

Note: As of Kafdrop 3.10.0, a ZooKeeper connection is no longer required. All necessary cluster information is retrieved via the Kafka admin API.

Open a browser and navigate to http://localhost:9000. The port can be overridden by adding the following config:

--server.port=<port> --management.server.port=<port>

Optionally, configure a schema registry connection with:

--schemaregistry.connect=http://localhost:8081

Finally, a default message format (e.g. to deserialize Avro messages) can optionally be configured as follows:

--message.format=AVRO

Valid format values are DEFAULT and AVRO. This can also be configured at the topic level via dropdown when viewing messages.

Running with Docker

Images are hosted at hub.docker.com/r/obsidiandynamics/kafdrop.

Launch container in background:

docker run -d --rm -p 9000:9000 \
    -e KAFKA_BROKERCONNECT=<host:port,host:port> \
    -e JVM_OPTS="-Xms32M -Xmx64M" \
    -e SERVER_SERVLET_CONTEXTPATH="/" \
    obsidiandynamics/kafdrop

Then access the web UI at http://localhost:9000.

Running in Kubernetes (using a Helm Chart)

Clone the repository (if necessary):

git clone https://github.com/obsidiandynamics/kafdrop && cd kafdrop

Apply the chart:

helm upgrade -i kafdrop chart --set image.tag=3.x.x \
    --set kafka.brokerConnect=<host:port,host:port> \
    --set server.servlet.contextPath="/" \
    --set jvm.opts="-Xms32M -Xmx64M"

For all Helm configuration options, have a peek into chart/values.yaml.

Replace 3.x.x with the image tag of obsidiandynamics/kafdrop. Services will be bound on port 9000 by default (node port 30900).

Note: The context path must end with a slash.

Proxy to the Kubernetes cluster:

kubectl proxy

Navigate to http://localhost:8001/api/v1/namespaces/default/services/http:kafdrop:9000/proxy.

Building

After cloning the repository, building is just a matter of running a standard Maven build:

$ mvn clean package

The following command will generate a Docker image:

mvn assembly:single docker:build

Docker Compose

There is a docker-compose.yaml file that bundles a Kafka/ZooKeeper instance with Kafdrop:

cd docker-compose/kafka-kafdrop
docker-compose up

APIs

JSON endpoints

Starting with version 2.0.0, Kafdrop offers a set of Kafka APIs that mirror the existing HTML views. Any existing endpoint can be returned as JSON by simply setting the Accept: application/json header. Some endpoints are JSON only:

• /topic: Returns a list of all topics.

Swagger

To help document the Kafka APIs, Swagger has been included. The Swagger output is available by default at the following Kafdrop URL:

/v2/api-docs

This can be overridden with the following configuration:

springfox.documentation.swagger.v2.path=/new/swagger/path

Currently only the JSON endpoints are included in the Swagger output; the HTML views and Spring Boot debug endpoints are excluded.

You can disable Swagger output with the following configuration:

swagger.enabled=false

CORS Headers

Starting in version 2.0.0, Kafdrop sets CORS headers for all endpoints. You can control the CORS header values with the following configurations:

cors.allowOrigins (default is *)
cors.allowMethods (default is GET,POST,PUT,DELETE)
cors.maxAge (default is 3600)
cors.allowCredentials (default is true)
cors.allowHeaders (default is Origin,Accept,X-Requested-With,Content-Type,Access-Control-Request-Method,Access-Control-Request-Headers,Authorization)

You can also disable CORS entirely with the following configuration:

cors.enabled=false

Actuator

Health and info endpoints are available at the following path: /actuator

This can be overridden with the following configuration:

management.endpoints.web.base-path=<path>

Guides

Connecting to a Secure Broker

Kafdrop supports TLS (SSL) and SASL connections for encryption and authentication. This can be configured by providing a combination of the following files (placed into the Kafka root directory):

• kafka.truststore.jks: specifying the certificate for authenticating brokers, if TLS is enabled.
• kafka.keystore.jks: specifying the private key to authenticate the client to the broker, if mutual TLS authentication is required.
• kafka.properties: specifying the necessary configuration, including key/truststore passwords, cipher suites, enabled TLS protocol versions, username/password pairs, etc. When supplying the truststore and/or keystore files, the ssl.truststore.location and ssl.keystore.location properties will be assigned automatically.

Using Docker

The three files above can be supplied to a Docker instance in base-64-encoded form via environment variables:

docker run -d --rm -p 9000:9000 \
    -e KAFKA_BROKERCONNECT=<host:port,host:port> \
    -e KAFKA_PROPERTIES=$(cat kafka.properties | base64) \
    -e KAFKA_TRUSTSTORE=$(cat kafka.truststore.jks | base64) \   # optional
    -e KAFKA_KEYSTORE=$(cat kafka.keystore.jks | base64) \       # optional
    obsidiandynamics/kafdrop

Environment Variables

Basic configuration

Name	Description
KAFKA_BROKERCONNECT	Bootstrap list of Kafka host/port pairs. Defaults to localhost:9092.
KAFKA_PROPERTIES	Additional properties to configure the broker connection (base-64 encoded).
KAFKA_TRUSTSTORE	Certificate for broker authentication (base-64 encoded). Required for TLS/SSL.
KAFKA_KEYSTORE	Private key for mutual TLS authentication (base-64 encoded).
SERVER_SERVLET_CONTEXTPATH	The context path to serve requests on (must end with a /). Defaults to /.
SERVER_PORT	The web server port to listen on. Defaults to 9000.

Advanced configuration

Name	Description
JVM_OPTS	JVM options.
JMX_PORT	Port to use for JMX. No default; if unspecified, JMX will not be exposed.
HOST	The hostname to report for the RMI registry (used for JMX). Defaults to localhost.
KAFKA_PROPERTIES_FILE	Internal location where the Kafka properties file will be written to (if KAFKA_PROPERTIES is set). Defaults to kafka.properties.
KAFKA_TRUSTSTORE_FILE	Internal location where the truststore file will be written to (if KAFKA_TRUSTSTORE is set). Defaults to kafka.truststore.jks.
KAFKA_KEYSTORE_FILE	Internal location where the keystore file will be written to (if KAFKA_KEYSTORE is set). Defaults to kafka.keystore.jks.

Using Helm

Like in the Docker example, supply the files in base-64 form:

helm upgrade -i kafdrop chart --set image.tag=3.x.x \
    --set kafka.brokerConnect=<host:port,host:port> \
    --set kafka.properties="$(cat kafka.properties | base64)" \
    --set kafka.truststore="$(cat kafka.truststore.jks | base64)" \
    --set kafka.keystore="$(cat kafka.keystore.jks | base64)"

Updating the Bootstrap theme

Edit the .scss files in the theme directory, then run theme/install.sh. This will overwrite src/main/resources/static/css/bootstrap.min.css. Then build as usual. (Requires npm.)

Securing the Kafdrop UI

Kafdrop doesn't (yet) natively implement an authentication mechanism to restrict user access. Here's a quick workaround using NGINX using Basic Auth. The instructions below are for macOS and Homebrew.

Requirements

• NGINX: install using which nginx > /dev/null || brew install nginx
• Apache HTTP utilities: which htpasswd > /dev/null || brew install httpd

Setup

Set the admin password (you will be prompted):

htpasswd -c /usr/local/etc/nginx/.htpasswd admin

Add a logout page in /usr/local/opt/nginx/html/401.html:

<!DOCTYPE html>
<p>Not authorized. <a href="<!--# echo var="scheme" -->://<!--# echo var="http_host" -->/">Login</a>.</p>

Use the following snippet for /usr/local/etc/nginx/nginx.conf:

worker_processes 4;
  
events {
  worker_connections 1024;
}

http {
  upstream kafdrop {
    server 127.0.0.1:9000;
    keepalive 64;
  }

  server {
    listen *:8080;
    server_name _;
    access_log /usr/local/var/log/nginx/nginx.access.log;
    error_log /usr/local/var/log/nginx/nginx.error.log;
    auth_basic "Restricted Area";
    auth_basic_user_file /usr/local/etc/nginx/.htpasswd;

    location / {
      proxy_pass http://kafdrop;
    }

    location /logout {
      return 401;
    }

    error_page 401 /errors/401.html;

    location /errors {
      auth_basic off;
      ssi        on;
      alias /usr/local/opt/nginx/html;
    }
  }
}

Run NGINX:

nginx

Or reload its configuration if already running:

nginx -s reload

To logout, browse to /logout.