There’s a bunch of improvements in the works for how ksqlDB handles code deployments and migrations. For now though, for deploying queries there’s the option of using headless mode (which is limited to one query file and disables subsequent interactive work on the server from a CLI), manually running commands (yuck), or using the REST endpoint to deploy queries automagically. Here’s an example of doing that.
The FilePulse connector from Florian Hussonnois is a really useful connector for Kafka Connect which enables you to ingest flat files including CSV, JSON, XML, etc into Kafka. You can read more it in its overview here. Other connectors for ingested CSV data include kafka-connect-spooldir (which I wrote about previously), and kafka-connect-fs.
Here I’ll show how to use it to stream CSV data into a topic in Confluent Cloud. You can apply the same config pattern to any other secured Kafka cluster.
Using ksqlDB in Confluent Cloud makes things a whole bunch easier because now you just get to build apps and streaming pipelines, instead of having to run and manage a bunch of infrastructure yourself.
Once you’ve got ksqlDB provisioned on Confluent Cloud you can use the web-based editor to build and run queries. You can also connect to it using the REST API and the ksqlDB CLI tool. Here’s how.
The ActiveMQ source connector creates a Struct holding the value of the message from ActiveMQ (as well as its key). This is as would be expected. However, you can encounter challenges in working with the data if the ActiveMQ data of interest within the payload is complex. Things like converters and schemas can get really funky, really quick.
The Kafka Connect JDBC Sink can be used to stream data from a Kafka topic to a database such as Oracle, Postgres, MySQL, DB2, etc.
It supports many permutations of configuration around how primary keys are handled. The documentation details these. This article aims to illustrate and expand on this.
I got the error SQLSyntaxErrorException: BLOB/TEXT column 'MESSAGE_KEY' used in key specification without a key length with Kafka Connect JDBC Sink connector (v10.0.2) and MySQL (8.0.23)
ksqlDB is a fantastically powerful tool for processing and analysing streams of data in Apache Kafka. But sometimes, you just want a quick way to profile the data in a topic in Kafka. I wrote about this previously with a convoluted (but effective) set of bash commands pipelined together to perform a GROUP BY on data. Then someone introduced me to visidata, which makes it all a lot quicker!
Whilst Apache Kafka is an event streaming platform designed for, well, streams of events, it’s perfectly valid to use it as a store of data which perhaps changes only occasionally (or even never). I’m thinking here of reference data (lookup data) that’s used to enrich regular streams of events.
You might well get your reference data from a database where it resides and do so effectively using CDC - but sometimes it comes down to those pesky CSV files that we all know and love/hate. Simple, awful, but effective. I wrote previously about loading CSV data into Kafka from files that are updated frequently, but here I want to look at CSV files that are not changing. Kafka Connect simplifies getting data in to (and out of) Kafka but even Kafka Connect becomes a bit of an overhead when you just have a single file that you want to load into a topic and then never deal with again. I spent this afternoon wrangling with a couple of CSV-ish files, and building on my previous article about neat tricks you can do in bash with data, I have some more to share with you here :)
Some people learn through doing - and for that there’s a bunch of good ksqlDB tutorials here and here. Others may prefer to watch and listen first, before getting hands on. And for that, I humbly offer you this little series of videos all about ksqlDB. They’re all based on a set of demo scripts that you can run for yourself and try out.
🚨 Make sure you subscribe to my YouTube channel so that you don’t miss more videos like these!
One of the fun things about working with data over the years is learning how to use the tools of the day—but also learning to fall back on the tools that are always there for you - and one of those is bash and its wonderful library of shell tools.
There’s an even better way than I’ve described here, and it’s called visidata. I’ve written about it more over here.
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I’ve been playing around with a new data source recently, and needed to understand more about its structure. Within a single stream there were multiple message types.
tl;dr: specify the --user root argument:
docker exec --interactive \
--tty \
--user root \
--workdir / \
container-name bashConfluent Cloud is not only a fully-managed Apache Kafka service, but also provides important additional pieces for building applications and pipelines including managed connectors, Schema Registry, and ksqlDB. Managed Connectors are run for you (hence, managed!) within Confluent Cloud - you just specify the technology to which you want to integrate in or out of Kafka and Confluent Cloud does the rest.
When Kafka Connect ingests data from a source system into Kafka it writes it to a topic. If you have set auto.create.topics.enable = true on your broker then the topic will be created when written to. If auto.create.topics.enable = false (as it is on Confluent Cloud and many self-managed environments, for good reasons) then you can tell Kafka Connect to create those topics first. This was added in Apache Kafka 2.6 (Confluent Platform 6.0) - prior to that you had to manually create the topics yourself otherwise the connector would fail.
KIP-66 was added in Apache Kafka 0.10.2 and brought new functionality called Single Message Transforms (SMT). Using SMT you can modify the data and its characteristics as it passes through Kafka Connect pipeline, without needing additional stream processors. For things like manipulating fields, changing topic names, conditionally dropping messages, and more, SMT are a perfect solution. If you get to things like aggregation, joining streams, and lookups then SMT may not be the best for you and you should head over to Kafka Streams or ksqlDB instead.
Apache Kafka 2.6 included KIP-585 which adds support for defining predicates against which transforms are conditionally executed, as well as a Filter Single Message Transform to drop messages - which in combination means that you can conditionally drop messages.
As part of Apache Kafka, Kafka Connect ships with pre-built Single Message Transforms and Predicates, but you can also write you own. The API for each is documented: Transformation / Predicate. The predicates that ship with Apache Kafka are:
RecordIsTombstone - The value part of the message is null (denoting a tombstone message)
HasHeaderKey- Matches if a header exists with the name given
TopicNameMatches - Matches based on topic
The ReplaceField Single Message Transform has three modes of operation on fields of data passing through Kafka Connect:
Include only the fields specified in the list (whitelist)
Include all fields except the ones specified (blacklist)
Rename field(s) (renames)
Over the years I’ve used various blogging platforms; after a brief dalliance with Blogger I started for real with the near-inevitable Wordpress.com. From there I decided it would be fun to self-host using Ghost, and then almost exactly two years ago to the day decided it definitely was not fun to spend time patching and upgrading my blog platform instead of writing blog articles, so headed over to my current platform of choice: Hugo hosted on GitHub pages. This has worked extremely well for me during that time, doing everything I want from it until recently.
The Cast Single Message Transform lets you change the data type of fields in a Kafka message, supporting numerics, string, and boolean.
