They are called streaming data "pipe"lines... right?

The (long but what’s new) article you’re reading is the background story of TypeStream, an open-source streaming platform that allows you to write and run typed data pipelines with a minimal, familiar syntax. It’s the tale of how an intuition I had almost a decade ago developed into the three foundational ideas that make TypeStream look like this:

cat /dev/kafka/local/topics/page_views |
enrich { v -> http "{$v.ip_address}" }

I tried my best to make sections independent but I recommend reading them in order as they’re connected to each other the way they’re presented:

TypeStream is a young project so it changes all the time. Some features are already implemented and others are being worked on. The official TypeStream discord server is the best way to ask roadmap questions.

The first intuition #

Almost a decade ago, I was the CTO at Marley Spoon, a small and cool startup making the best meal kit delivery service.

One day, this must have been spring of 2016, I was in a meeting with the engineering and product leadership. We were discussing how to leverage Kafka so that our teams could work more independently.

We had a web store and some batch jobs “producing” orders and a variety of services “consuming” them to implement a variety of use-cases. Kafka acted as a transport layer and a “api” between the two worlds via a change data capture pipeline. I’m sure this architecture is familiar to many of you, especially now that change data capture is widely known. Back then, it was a bit more novel so my team was a little hesitant.

The consuming side of this architecture intrigued me: there were too many abstraction levels between our conversation and our tooling. It felt clumsy and inefficient to me.

Now before I explain what I mean with “abstraction levels” in the context of that meeting, let me clarify that I’m specifically talking about abstraction in the context of developer experience. The obvious point being that we didn’t create programming languages because they were better than assembly for the machine. We did new abstractions to improve developer experience. They’re called “high level programming languages” exactly because they’re several levels of abstraction away from the machine needs.

Of course a mismatch between the abstraction level at which humans discuss some technical problem and the one their tooling provides is to be expected. The point is that the closer the two abstraction levels are, the more productive humans can be.

Now that I clarified I’m talking about developer experience, let me go back to the meeting where I first thought of this mismatch in the context of data pipelines.

Here’s the scenario: we streamed orders to Kafka with a rudimental (by today’s standards) change data capture pipeline. Almost no consumer needed every order, most needed a subset of orders (things like “orders to ship”, “orders to pack in NL”) or parts of a subset (things like “customer’s emails of orders to ship”, “list of ingredients of orders to pack in NL”).

Data operations like “orders to ship” and “list of ingredients of orders to pack in NL” were conceptually simple. But, in practice, extracting data from Kafka topics, process them, and then send them around to other services required us to discuss lots of details. The serialization format of the data, the schema (what if it changes?), the actual streaming application (what language we write this in?). Everything about it felt very low level and broke our ability to think about these problems at a high enough level of abstraction.

Looking at diagrams on a whiteboard I couldn’t help but think that most of our data pipelines were composable little functions. We could combine them by calling each function on the result of the previous one. A more mathematically inclined person would have explored this concept further but I’m a programmer so I saw a different, I dare to say, more obvious metaphor at play. These little functions you can call one after the other looked a lot like UNIX pipelines. Each function type is a UNIX command that does one thing, calling them in sequence is just a command pipe.

This intuition about abstraction level mismatch between tooling and data operations lead me to ask myself what if we could express data pipelines like UNIX pipelines? TypeStream is my answer to that question.

Data pipelines are UNIX pipelines #

If we had TypeStream back at MarleySpoon, getting orders to ship may look like this:

let orders_to_ship=$(cat orders | grep [.state == 'to_ship'])

Getting emails something like this:

cat $orders_to_ship | cut .email

It felt right to me but it also confused me because, for the first time in my career, I wanted to build something that I found both really obvious and pretty hard to build. In fact, I didn’t even try building a prototype back then. I had no idea how to write my own programming language and Kafka Streams (which is TypeStream only runtime right now, more on this later) was very young. Also, in spring 2016, I knew nothing about Kafka Streams.

Nowadays, the experience got much better. Thanks to amazing progress of technology like Kafka Streams, ksqlDB, and flink, you can reason about streaming data pipelines at a much higher level. The Kafka community made great progress. We made big abstraction jumps from “here is the consumer group api javadoc” to Kafka Streams, ksqlDB, flink (to name a few). The thing is though… it’s not high-level enough ๐Ÿ™ƒ

What is high level enough then? Well, UNIX pipelines are almost English. That is high level enough for me. This is TypeStream’s first foundational idea: data pipelines are UNIX pipelines.

At some point last year, I decided I had to look at Kotlin more closely. The project “write a bash-like pipe to Kafka Streams applications compiler” was the kind of project I needed to learn the language. There’s no direct connection between Kotlin and TypeStream but I can’t learn a new programming language through fictional exercises. I need something complex enough I can go at it for a few weeks in a row. So here I was, finally trying to go one more level up the ladder of abstraction I already wanted all the way back in spring of 2016.

The first few weeks were really fun. I got to put in practice a big chunk of the Crafting interpreters, a magnificent book that gets you started on writing a programming language and not on talking about writing one. By the time I could compile trivial pipelines I had spent quite some time thinking about TypeStream and discovered two more ideas that, together with “data pipelines are UNIX pipelines”, make the foundation of what TypeStream is today.

Everything is a stream #

Because I’m a pretty sceptical person that likes to sabotage their own plans (I’m fun like that), while prototyping TypeStream I found myself in a strange two-step self-feeding feedback loop:

  1. I asked myself something along the lines of “well if TypeStream were a good idea, then you could do X but sure you can’t, right?”
  2. I immediately found solid answers via the “UNIX metaphor”. I was happy for a minute and then back to 1.

This is where TypeStream’s second foundational idea comes in. See, when I had the intuition of expressing a pipeline like, say, “filter book by word count > 20k” as a UNIX pipe, I didn’t go any further than imagining this:

cat /dev/kafka/cluster1/topics/books | grep [.word_count > 20_000]

By the time I had a working compiler and was running my first TypeStream pipeline, I realized there was a second powerful idea hiding in plain sight: the virtual filesystem.

In UNIX, everything is a file. In TypeStream, everything is a stream.

It’s obvious: the core metaphor doesn’t work without a filesystem!

Addressing data sources as filesystem paths felt so natural that I didn’t immediately realize its profound implications. For example, how would you expect to address a postgres table? Does /dev/postgres/db1/tables/customers look reasonable? I think it does. When I pitch TypeStream to backend developers or data engineers, this is completely obvious for them. There are no questions about the general idea of how a “data mesh filesystem” should look like.

While it’s natural to think of data sources as filesystem paths, it may be a little harder to see how well this idea fits with typical data operations. For example, you may want to expose data via a websocket this way:

cat /dev/kafka/cluster1/topics/books |
grep The                             |
cut .id .title > /media/websocket/server1/books_notifications

“mounting” external “media” works great, right? Think of /media/elastic/cluster1/index_01 or /media/http/server1/endpoint. Why not? It looks so natural.

Now let me put these two foundational ideas together to imagine how TypeStream would deal with some common scenario. For example: stream data out of a relational database, apply some business filtering to it, send the filtered data around. A concrete, trivial, real-world example of this scenario is sign-up flow processes.

Here’s how I imagine TypeStream taking care of capturing new users out of a postgres database, publish them to some Kafka topic for later consumption, and send a welcome email to new users via a transactional email service:

let new_users = $(cat /dev/postgres/tables/users | grep [.op == 'insert'])

cat $new_users > /dev/kafka/topics/
cat $new_users | cut .id .email > /media/email/welcome

It’s surprisingly succinct. But brevity isn’t the focus, that’s the accidental benefit of good abstraction. The win is that TypeStream gives you clarity and brevity. This example is very succinct but lost almost none of the clarity of the natural language description.

The abstraction levels are now close enough that some tech already covers the gap between TypeStream and natural language. GitHub Copilot, for example, produces valid TypeStream pipelines from plain English comments very often! A testament to the simplicity and validity of the core ideas behind TypeStream.

After all, I invented nothing and I take no credit: UNIX pipes were there long before I was born.

It is called TypeStream for a reason #

At this point, if you may be wondering how does TypeStream take care of things like cat $new_users | cut .id .email? What’s the secret ingredient that makes it so simple and succinct?

This is where the third foundational idea comes in. It may seem less relevant to the conversation because it doesn’t directly borrow (I mean steal) from UNIX. On the other hand though, it’s so important to the developer experience it gave TypeStream its name.

TypeStream can type-check pipelines before you run them. It has a key-value store where keys are filesystem paths and values are serialization format independent schema types. A key value pair looks like this:

/dev/kafka/cluster1/topics/books=Struct[title: String, wordCount: Int]

So when you’re trying to run the following pipeline:

cat /dev/kafka/cluster1/topics/books | grep [.name ~= "the"]

the compiler tells you “hey there’s no name field on books” and spare you the pain of finding out later in the process.

The types metadata also help TypeStream by allowing its user a notable omission in their TypeStream pipelines: there’s no mention of serialization formats anywhere. Is this topic avro, protobuf, json schema? The question is irrelevant to designing a data pipeline. If you know the shape of the data you’re working with, its serialization format is irrelevant to you.

One day, while prototyping the type checker, I realized TypeStream had enough metadata information to also do some type inference on data pipelines.

Since the compiler knows the schema type of each “path” and knows the effect of each data operator on a schema type, it can infer the resulting schema types of each pipeline. Consider these examples:

cat /dev/kafka/cluster1/topics/books | cut .id .title > /media/http/server1/endpoint

TypeStream can infer that the resulting schema type is something like Struct[id: String, title: String] and produce reasonable JSON for the “HTTP media”. Again, it’s about developer experience: you don’t need to specify the shape of the resulting data set, TypeStream can figure it out. It also works with more complex pipelines. Consider a “typical” enrichment pipeline:

cat /dev/kafka/cluster1/topics/page_views                  |
enrich {p -> http "" | cut .country} |
wc --by .country

Here, the compiler calculates the resulting type by “merging” page views with the shape of “something with a string country field” that the enrichment block produces. And then use that resulting type to type-check that --by .country option. If you’d be redirecting this pipeline to, say, a redis store, TypeStream would use the resulting schema type to make an informed decision on which data structure to create it. Once again, it’s about developer experience: TypeStream abstracts so many irrelevant details away by leveraging “ancient” programming concepts like UNIX pipelines and filesystem paths.

The power of abstraction #

I want to conclude this article the way I started it: discussing abstractions. While pitching TypeStream I learned that some powerful abstractions TypeStream enables are not obvious. But they’re equally important to the developer experience so let me get to them.

Abstractions outlive implementations #

A tweet by Gunnar Morling:

An interesting recurring theme in data infra: protocols/APIs outliving specific implementations. E.g. #Kafka wire protocol (#RedPanda, #WarpStream as alternative providers), S3 API (#MinIO, #Ceph, etc.), #Postgres protocol (too many to list even).

applies perfectly well to TypeStream which may not be obvious unless we consider the implications of its technical implementation.

At its very core, TypeStream is a “remote compiler”: you give it some bash-like code and TypeStream compiles it into a Kafka Streams application and run that for you.

The key point is that, exactly because it’s a compiler, Kafka Streams is “just” a runtime. A powerful and easy to use runtime which is why I started with it. But it’s not the only possible runtime. TypeStream could compile pipelines into flink jobs, pulsar applications, google pub/sub pipelines, whatever. TypeStream can outlive its runtime because it’s also a small programming language so it can abstract away the runtime for you. In fact, it already does: there’s no mention of Kafka Streams in a TypeStream pipeline.

I don’t want to bash SQL but #

As Sarah Catanzaro once said: abstractions matter.

The way I read her remark is that abstractions greatly contribute to the developer experience. The fewer new concepts you have to learn, the quicker you’ll get things done.

The argument here is: if you know UNIX pipelines, you know TypeStream. There are no new abstractions. Pipes and redirections apply to data naturally. Files are data. Streams are data. Almost nothing to learn.

There’s also a bolder hidden claim here: UNIX pipelines are a better abstraction for data pipelines than SQL-like languages are. The right abstraction wins over “better” syntax.

TypeStream and SQL-like languages are more or less at the same abstraction level but I think TypeStream fits the problem space better because of the three foundation ideas I discussed:

  • data pipelines are unix pipelines. Most UNIX commands have natural streaming/data operations counterpart (did you know there’s a join command in UNIX? That’s what I mean!)
  • A virtual filesystem hides lots of details. You don’t need any special syntax to configure/interact with external sources (“media mounting”).
  • TypeStream treats types like a strongly typed programming language would. It already has basic type checking and basic inference. In the future, it’ll allow you, for example, to refactor data pipelines across a whole organization automatically. Just like your favourite strongly typed language does.

To be clear, I love SQL. There’s nothing better in the scenario “I got this data question, give me the answer?”. I apply this principle to code too. Meaning, no-orm for me. So I’m really not trying to bash SQL here, there’s nothing wrong with it. I’m saying they’re called data pipe-lines so a “pipe-oriented” (my term) language fits the problem better.

Naming is hard #

Telling people what TypeStream is in a few word has proven the most challenging aspect of the journey so far. I’m not familiar with any good cultural equivalent, meaning I can’t say something like “TypeStream is X for streaming data pipelines”, so I struggle to find quick shortcuts. The unknown variable here is unclear because TypeStream is a small programming language but also a platform? I settled for this:

TypeStream is an open-source streaming platform that allows you to write and run typed data pipelines with a minimal, familiar syntax.

This is a good first attempt at describing something that uses well-known abstractions in a novel way. I say “naming is hard” because I’m not convinced “platform” conveys well enough the abstraction TypeStream puts in place here. TypeStream isn’t just a compiler. It is also an orchestrator for data pipelines. The official TypeStream CLI has a run command that looks like this:

typestream run <source-code>

When you invoke this command, TypeStream compiles your code and, given there are no errors (type-checking is nice!), it launches your pipeline inside a Kubernetes job. The interesting bit here is that TypeStream abstracts the runtime of your pipelines away. There’s no mention anywhere in your source code that it will run in production as a Kafka Streams application. That’s because Kafka Streams is just a runtime and if your pipeline should run as, say, a pulsar application, TypeStream will happily compile your source code to it and run it for you.

Note that here I’m talking about a different idea than “just outliving” a runtime. As a platform, “TypeStream” abstracts both where and how your data pipelines runs. In theory, knowing the shape of your data and what to do with them is all you need to write and run a data pipeline. In practice, it’s not that easy. That’s TypeStream core argument: it could so it should be that easy.