I talk and write about Kafka and Confluent Platform a lot, and more and more of the demos that I’m building are around Confluent Cloud. This means that I don’t have to run or manage my own Kafka brokers, Zookeeper, Schema Registry, KSQL servers, etc which makes things a ton easier. Whilst there are managed connectors on Confluent Cloud (S3 etc), I need to run my own Kafka Connect worker for those connectors not yet provided. An example is the MQTT source connector that I use in this demo. Up until now I’d either run this worker locally, or manually build a cloud VM. Locally is fine, as it’s all Docker, easily spun up in a single docker-compose up -d command. I wanted something that would keep running whilst my laptop was off, but that was as close to my local build as possible—enter GCP and its functionality to run a container on a VM automagically.

You can see the full script here. The rest of this article just walks through the how and why.

This is based on using Confluent Cloud to provide your managed Kafka and Schema Registry. All that you run yourself is the Kafka Connect worker.

Optionally, you can use this Docker Compose to run the worker and a sample MySQL database.

I use the Elastic stack for a lot of my talks and demos because it complements Kafka brilliantly. A few things have changed in recent releases and this blog is a quick note on some of the errors that you might hit and how to resolve them. It was inspired by a lot of the comments and discussion here and here.

When you create a sink connector in Kafka Connect, by default it will start reading from the beginning of the topic and stream all of the existing—and new—data to the target. The setting that controls this behaviour is auto.offset.reset, and you can see its value in the worker log when the connector runs:

Kafka Connect has as REST API through which all config should be done, including removing connectors that have been created. Sometimes though, you might have reason to want to manually do this—and since Kafka Connect running in distributed mode uses Kafka as its persistent data store, you can achieve this by manually writing to the topic yourself.

Here’s a hacky way to automatically restart Kafka Connect connectors if they fail. Restarting automatically only makes sense if it’s a transient failure; if there’s a problem with your pipeline (e.g. bad records or a mis-configured server) then you don’t gain anything from this. You might want to check out Kafka Connect’s error handling and dead letter queues too.

Kafka Connect configuration is easy - you just write some JSON! But what if you’ve got credentials that you need to pass? Embedding those in a config file is not always such a smart idea. Fortunately with KIP-297 which was released in Apache Kafka 2.0 there is support for external secrets. It’s extendable to use your own ConfigProvider, and ships with its own for just putting credentials in a file - which I’ll show here. You can read more here.