Comet

Horizon component for the delivery and redelivery of eventMessages with deliveryType callback.

Prerequisites • Building Comet • Configuration • Running Comet

Overview

Horizon Comet is one of the central components for the delivery of event messages. It handles the delivery and redelivery of event messages to callback endpoints of subscribed consumers and provides retry mechanisms.

Note: Comet is an essential part of the Horizon ecosystem. Please refer to documentation of the entire system to get the full picture.

Prerequisites

For the optimal setup, ensure you have:

A running instance of Kafka
Access to a Kubernetes cluster on which the Subscription (subscriber.horizon.telekom.de) custom resource definition has been registered

Gradle build

./gradlew build

Docker build

The default docker base image is azul/zulu-openjdk-alpine:21-jre. This is customizable via the docker build arg DOCKER_BASE_IMAGE. Please note that the default helm values configure the kafka compression type snappy which requires gcompat to be installed in the resulting image. So either provide a base image with gcompat installed or change/disable the compression type in the helm values.

docker build -t horizon-comet:latest --build-arg="DOCKER_BASE_IMAGE=<myjvmbaseimage:1.0.0>" .

Multi-stage Docker build

To simplify things, we have also added a mult-stage Dockerfile to the respository, which also handles the Java build of the application in a build container. The resulting image already contains "gcompat", which is necessary for Kafka compression.

docker build -t horizon-comet:latest . -f Dockerfile.multi-stage

Configuration

Comet configuration is managed through environment variables. Check the complete list of supported environment variables for setup instructions.

Running Comet

Locally

Before you can run Comet locally you must have a running instance of Kafka locally or forwarded from a remote cluster. Additionally, you need to have a Kubernetes config at ${user.home}/.kube/config.main that points to the cluster you want to use.

After that you can run Comet in a dev mode using this command:

./gradlew bootRun

Documentation

Read more about the software architecture and the general process flow of Horizon Comet in docs/architecture.md.

Contributing

We're committed to open source, so we welcome and encourage everyone to join its developer community and contribute, whether it's through code or feedback.
By participating in this project, you agree to abide by its Code of Conduct at all times.

Code of Conduct

This project has adopted the Contributor Covenant in version 2.1 as our code of conduct. Please see the details in our CODE_OF_CONDUCT.md. All contributors must abide by the code of conduct.

By participating in this project, you agree to abide by its Code of Conduct at all times.

Licensing

This project follows the REUSE standard for software licensing. You can find a guide for developers at https://telekom.github.io/reuse-template/.
Each file contains copyright and license information, and license texts can be found in the ./LICENSES folder. For more information visit https://reuse.software/.

telekom / pubsub-horizon-comet