Event-Driven Microservices: A Comparative Analysis of Kafka Streams and TypeStream

When I’m talking about TypeStream to people, I often get asked:

How does TypeStream compare to Kafka Streams when building microservices?

It’s more than a fair question; the functional overlap between the two technologies is large. After all, Kafka Streams is TypeStream’s default runtime.

To answer the question as concretely as possible, I explain what I mean by “event-driven microservices”, then, with the help of a purposely trivial problem, I look at how Kafka Streams and TypeStream. Finally, I compare the two technologies in terms of developer experience and deployment model.

Here’s the table of contents if you’d like to jump to a specific section:

Event-driven microservices #

I think the naming “event-driven microservices” is off and it has been forced into our conversations by a larger trend (read cult) about microservices.

I prefer the naming “streaming applications” because I like to call things what they are and what they do but I stick with “event-driven microservice” because this naming has a wider reach and who doesn’t want that?

All right, now you know I’m reluctantly saying “event-driven microservice” but what do I mean anyway?

An “event-driven microservice” is a small streaming application microservice that does its job by consuming and producing off an event broker. More often than not, the event broker of choice is a Kafka cluster because event-driven microservice architectures favour durable events that can be consumed many times by many different services (as opposed as messages passed around using a “traditional” queue). Kafka is an obvious choice to unlock the full potential of this approach.

Here’s a trivial example diagram of this architecture:

event-driven sample architecture diagram

From this point on, when I say event-driven microservice, I’m always talking about a small application (see?) that consumes data from one or more Kafka topics, does its thing, and (often) sends its result back to a Kafka Topic.

I’m ignoring how tricky it is to define what a “small” application is. I could probably write a whole article about it (people wrote books about slightly, ehm, larger topics) so it’s out of scope here.

For the sake of the discussion, let’s assume we have a application.books topic where records look like this:

{"id":1,"title":"Station Eleven","word_count":45000,"author_id":"42"}
{"id":2,"title":"Sea of Tranquility","word_count":40000,"author_id":"42"}
{"id":3,"title":"Purple Hibiscus","word_count":35000,"author_id":"24"}

I’m using JSON for readability but, in a production system, I’d expect Avro (or Protocol Buffers) to be the serialization format of choice (and would also use UUID for ids).

Let’s also imagine we need novels into a different topic so that other microservices can solve novel specific problems without having to compute what a novel is from books.

Initially, the way we define novel is trivial (> 40K words) but we expect this to change over time so an event-driven microservice that is responsible to extract novels from the application.books topic into a application.novels topic is a perfect fit.

Now that (hopefully) the context is clearer and we also have a trivial example to work with, let’s look at what Kafka Streams and TypeStream are and how they can solve such a problem.

Kafka Streams #

In the words of the official docs:

Kafka Streams is a client library for building applications and microservices, where the input and output data are stored in Kafka clusters. It combines the simplicity of writing and deploying standard Java and Scala applications on the client side with the benefits of Kafka’s server-side cluster technology.

The Kafka Streams authors believe that the library is a good fit for our use case. It goes without saying that I agree with them.

Kafka Streams is a fantastic library! It has a very usable API and covers a lot of ground with its features. I wrote about it in Getting started with Kafka Streams which, believe me I feel weird saying this myself, is the best introduction to the library if you know nothing about it.

Here’s a Java program that uses Kafka Streams to solve this problem:

final StreamsBuilder builder = new StreamsBuilder();

final Properties streamsConfiguration = new Properties();
streamsConfiguration.put(StreamsConfig.APPLICATION_ID_CONFIG, "me.lucapette.novels");
streamsConfiguration.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
streamsConfiguration.put(AbstractKafkaSchemaSerDeConfig.SCHEMA_REGISTRY_URL_CONFIG, "http://localhost:8081");
streamsConfiguration.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());
streamsConfiguration.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, SpecificAvroSerde.class);

final KStream<String, Book> source = builder.stream("application.books");

source.filter((key, book) -> book.getWordCount() > 40_000).to("application.novels");

final KafkaStreams streams = new KafkaStreams(builder.build(), streamsConfiguration);

Apart from the imports and some function definitions, this is pretty much all the code we need that extracts novels from a stream of books. Sweet. If you’d like to play around with this code, I have an example repo on GitHub: lucapette/kafka-streams-vs-typestream.

TypeStream #

TypeStream is an open-source streaming platform that allows you to write and run typed data pipelines with a minimal, familiar UNIX-like syntax. I wrote about the fundamental ideas that drive the project in they’re called streaming data “pipe"lines… right?.

Here’s how filtering novels looks like in TypeStream:

cat /dev/kafka/cluster/topics/application.books |
grep [ .wordCount > 40000] > /dev/kafka/cluster/topics/application.novels

This looks very different of course and I think we’re read to dive into a comparison. If you’d like to play around with this, head to the official TypeStream getting started guide.

The developer experience #

We’re talking about two different programming languages here so the developer experience is different.

Kafka Streams is a Java library so anything JVM works for you. That’s not a limiting choice if you like at least one JVM language. I’ve build Kafka Streams applications with Java and Kotlin and the experience is very pleasant. JVM programming languages are always a choice: great communities, great tooling. Of course, if you’re not familiar or willing to work with any of the JVM languages then you’re out of luck.

TypeStream, on the other hand, is almost bash. If you’re familiar with UNIX systems, you’re already familiar with TypeStream. I think that’s a great selling point especially for beginners. You may know nothing about streaming and still be able write an event-driven microservice with TypeStream. Bash may not be the most solid language out there for large applications but:

  • Everyone knows enough to write a small data pipeline with it.
  • We’re talking about microservices so we expect our applications to be small.

The developer workflow is also different. With Kafka Streams, you’re in a traditional “backend workflow”. You write your app, you write your tests, then you package it and ship it. Nothing wrong with it. In fact, since it’s JVM, the tooling is pretty amazing (one of my fav examples: test containers).

In TypeStream, you have a REPL you can use to quickly verify your code. Once you’re ready, you run typestream run <source-code> and TypeStream will deploy the microservice for you. In general, it’s clear that TypeStream’s workflow is more data oriented than application oriented.

There’s one more difference that it’s not obvious but pretty profound. Let’s look at the code one more time. The Kafka Streams version:

final KStream<String, Book> source = builder.stream("application.books");

source.filter((key, book) -> book.getWordCount() > 40_000).to("application.novels");

and the TypeStream one:

cat /dev/kafka/cluster/topics/application.books | grep [ .word_count > 40000] > /dev/kafka/cluster/topics/application.novels

Since these two pieces of code solve the same problem, they obviously look very similar. The key difference is that how the two approach serialization.

In the Kafka Streams version, you’re responsible for the serialization yourself. That KStream<String, Book> looks innocent but I’ve seen lots of newcomers trip up on this specific point. You have to instruct Kafka Streams to do the correct serialization. While that’s obviously fair from the API perspective, it gives a burden on developer experience that often feels unneeded. Avro and Protocol Buffer (to cite the most used ones) are fantastic at what they do but also involve lots of machinery with generated code and build setup. Furthermore, you have to point Kafka Streams to your schema registry so it often feels “unfair” that you still have to do all the serialization work “manually”.

The TypeStream code has no mention of serialization. You still have to tell your TypeStream server where your schema registry is but there’s no step two. TypeStream will associate the schema of your topics with file system paths and then use that metadata to “type check” your pipelines. That simplicity is reflected in the TypeStream code: less configuration, no explicit types.

The deployment model #

Since Kafka Streams is just a library (that “just” is meant as a huge compliment), the deployment model is whatever way you deploy JVM applications. Since Kafka Streams applications can be stateful, you may need to pay attention to the local disks (a bit tricky in Kubernetes). All in all, it’s a very flexible solution.

Technically speaking, TypeStream is a “remote compiler” that runs in a Kubernetes cluster and uses it for running jobs. That means two things:

  • You must deploy TypeStream in a Kubernetes cluster that has access to your Kafka clusters.
  • TypeStream will manage the lifecycle of your pipeline.

If you have a lot of very small services, this approach may be more convenient because yes you give up on flexibility (there’s one way to deploy TypeStream application and TypeStream will decide for you how to run them) but gain quite some velocity (once you wrote the pipeline, you’re done).

When to use what #

Comparing two technologies that can solve similar problems is always a little tricky because the differences may boil down to taste which doesn’t lead to constructive conversations. In this case, the design goals of the two can guide us toward a constructive approach.

Kafka Streams is a JVM library. It’s a fully-featured streaming processing library and has lots of advanced features (like interactive queries. Check out my HTTP endpoints with Kafka Streams Interactive Queries) so you can solve a vast number of problems with it.

TypeStream is a streaming platform that compiles your code into Kafka Streams applications. One of the non-goal of TypeStream is critical to this conversation: TypeStream doesn’t aim to cover every Kafka Streams feature. The project is concerned with what kind of problems can be expressed as UNIX pipelines and with improving the developer experience of writing streaming applications.

This means there are scenarios in which you won’t be able to use TypeStream even if you wanted to. On the other hand, the scenario we discussed in this article, event-driven microservices fits TypeStream well. Most microservices do one small thing (they should, no?) and can be expressed as a one-liner in TypeStream.

What I’m saying is that I would use TypeStream for trivial event-driven microservices and leave Kafka Streams for the more advanced problems. Yes, of course my answer is to use both 😁

Hey! 👋

Thank you for reading my content. I appreciate it.

If you like what you're reading, you may want to check out TypeStream.