söndag 18 april 2021

Confessions of an Open Source Contributor

I am one of the contributors to an Open Source project called zookeeper. It's an Apache ZooKeeper client made for Node.js. You can find the package on npm and the source code at GitHub.

What’s ZooKeeper?

"Apache ZooKeeper ... providing configuration information, naming, synchronization and group services over large clusters in distributed systems ..."

In short, Apache ZooKeeper is made of two parts: a service, and clients that communicate with it. Included in the packaging from Apache, there is a client made for the Java platform and also a C based client. You will most likely find one for your favorite language out there as a third party Open Source project.

Why joining Open Source?

A couple of years ago, I was part of a team in an organisation that use Apache ZooKeeper heavily. The team maintains a Node.js based app that communicates with a ZooKeeper service.

One day, the app began to raise strange warnings and unexpected errors. We looked into it and found out that the reason was probably caused by the client no longer being compatible with the API of the service.

There wasn't much happening in the client's repository:
unanswered questions from users, issues not taken care of and pull requests not being reviewed.

The project was abandoned.

So, we used a different client that seemed fairly updated and stable. The strange behavior in our app was now gone. Great! It worked on our machines and in production. All good!

🙋"Hey, team. I can't install your app on my Windows machine."

Sometimes other teams need to run our app locally for testing and such things. It turned out that our new client didn't support Windows at all.

Wait a minute, isn't Node.js supported in all major platforms? Well, yes. But this one is building a Native Node.js AddOn using bash scripts. Windows don't have that.


Even though it wasn't my fault only, all I could think of is that it was my fault. I have ruined it for the teams at this workplace.

What else to do than try fix it on my spare time? So, I grabbed the source code to try to understand what's going on behind the scenes.


And that's how my Open Source journey began: triggered by guilt and feeling ashamed.

Coding in the Dark

Late nights and weekends were spent trying to figure out how to solve this huge problem, including C/C++ code, CMake, bash and node-gyp.

One day, I figured it out. I had succeeded in making it work on Mac OS X, Linux and on Windows! The next day - a sunny morning in beautiful Stockholm - I went to the office smiling. Exhausted by the lack of sleep, but happy.


Do I have to fix everything? 😟

While struggling with the source code, I realized there were more things that should be fixed. By then, I also realized that this Open Source project suffered from similar issues as the one we had replaced earlier: there wasn't really that much activity in the repo.

This is probably a common pattern: you work with something on a daily basis and contribute to Open Source projects. The years go by, you drift way from the project, simply because you now work with other things unrelated to the project.

How to maintain an Open Source project

Instead of grabbing the next task to spend late nights and weekends with, I decided to learn more about how to maintain Open Source projects.

I found a very useful guideline at GitHub, and I began to add notes about all kinds of things I thought should be done. Other Open Source projects were using labels in a way that I liked, so I added labels like help-wanted and good-first-issue to most of the tasks.

I think labels can help people getting an overview of the tasks and to understand the degree of difficulty.

Every time a question comes up, or someone is filing a bug report, I have replied to most of them within a day or two. I think this is important. The person reporting will know there is someone that has actually received and read the message.

As a result, really nice things have happened. The project has received Pull Requests from people located all over the world. Solving a broad variation of things from typos in the docs, to rewrites of the source code to modern JavaScript.

What's happening today?

Today, I think the project is stable and working well. I don't work nights or weekends. Even though I have moved on and no longer work with ZooKeeper as before, the feedback from users is my main inspiration to keep on working. Also, the amount of users of the client looks pretty good.

It inspires me to do the best I can with the project.

Photo by Justin Lim on Unsplash

söndag 11 april 2021

Almost like Clojure

Practicing different programming languages has given me new insights in programming concepts, code styles and tools. My current crush is Clojure. I like the functional and data oriented style of it, the simplicity and minimalism. I think my favorite thing with Clojure, though, is how the REPL is used.

“What’s so cool about that repple thing?” 🧐

Testing at your fingertips 🚦

When using a code editor powered by a REPL, you can instantly evaluate variables, code blocks, functions or the entire file, just by a hitting a key combination. The result pops up right next to the cursor. This means that testing the code you currently write is at your fingertips. You are practicing a Deluxe version of Test Driven Development.

No copy-paste here 👮

It is not necessary to copy-paste code snippets into the actual REPL window or in a shell. In fact, you shouldn’t touch the REPL window at all. Because you don’t want to miss out on all the good stuff like autocomplete, hints and smart navigation that you have in your favorite editor.

For Clojurians only? 💭

I really would like to have a similar workflow in other languages too. It turns out there are some pretty good tools out there, the ones I’ve tried out so far are for JavaScript and ✨Emacs ✨.

Interactive JavaScript development 😍

Here’s me playing around with the node-zookeeper code. The cursor never leaves the editor window, the evaluation result is printed out in the Node.js REPL window to the right. More verbose than I’m used too in Clojure, but I think it works well.

Trying out code and ideas like this is a very nice workflow. I think you will find less need for debugging or console.log statements.

Keep on learning 📚

Learning a new programming language or tool can be really difficult, but also fun when the pieces finally start coming together. The knowledge gathered is something you can bring with you to other areas.

Have a look at my post about Emacs and my current configuration. The Node.js REPL feature is made possible using the js-comint package.

Photo by Marc-Olivier Jodoin on Unsplash

söndag 4 april 2021

Software as building blocks

There seems to be an ongoing trend in software development towards using monorepos. This trend is something I have seen especially in the Clojure community.

Polylith - a monorepo architecture

I like the way Polylith solves how to work with code using a components-first architecture. Similar to LEGO, components are building blocks. A component can be shared across apps, tools, libraries, serverless functions and services.

Read more here: Polylith gitbook

The last architecture you will ever need *

From the Polylith docs:

"... Polylith is a software architecture that applies functional thinking at the system scale. It helps us build simple, maintainable, testable, and scalable backend systems. ..."

Okay, backend systems. What about frontend systems? 🤔

I want to Polylith all the things

Is it possible to use the Polylith architecture for a code base that includes web apps? This is something that I have wanted to find out.

Here's my example repo.

In this repo, I’ve added backend Clojure code, frontend ClojureScript and also some glue in between in the form of cljc files. Cljc is Clojure code that can be consumed by both frontend and backend code. This makes it possible to share code across Clojure and ClojureScript, building things just like with LEGO bricks and baseplates.

All the things?

I'll leave the question if ClojureScript and Clojure really should live in the same ecosystem unanswered and hope to get feedback from you. In my example repo, I have put all components in the same place. Should the building blocks be separated somehow, or is it good enough to have both LEGO and DUPLO in the same box? What are your thoughts about it?

Do we still have the Polylith one-REPL experience?

Well, we can have a two-REPLs experience. One for Clojure, that run on top of the JVM, and one for ClojureScript on top of JavaScript. Running both will make REPL driven backend development and Interactive Web Development possible.

You can add and use new ClojureScript components while the REPL is running. Create the namespace and evaluate the function.

There is one thing that I have no solution for (yet). When creating a new ClojureScript component and evaluating the entire namespace at once, I get a compilation error in the ClojureScript REPL: file not on classpath. The ClojureScript REPL have to be restarted to reload new source paths.

But don't worry, you can still evaluate the individual functions in the namespace and they will be loaded as expected in the ClojureScript REPL.

Tooling support

Polylith has a very nice and useful tool to support creating building blocks and to verify the setup. You can create components, bases and projects - as long as it is Clojure. For ClojureScript, you will have to create components manually.

If you are lazy, like me, just create a component with the poly tool as you would for Clojure, and simply rename the file extension to cljs or cljc afterwards.

Editor support?

Your editor most likely has support for running both Clojure and ClojureScript simultaneously. Emacs is my favourite editor. Start the REPLs with the cider-jack-in-clj&cljs command and you're ready to go!

Two REPLS running (even though the Cider splash message is confusing)

* The quote is from Joakim Tengstrands and Furkan Bayraktars talk about Polylith at the FuncProg Sweden 2020 meetup.

Photo by Amélie Mourichon on Unsplash

söndag 14 mars 2021

Wake up, sleepy lambda

AWS Lambda functions with painfully slow start up times is a problem. But there's hope.

Clojure anywhere

After going through some of the 12 Stages of learning Clojure, I have found this Lisp style language to be very nice and it has become my favorite programming language.

Some of the nice things with Clojure are that data is immutable, the REPL is like magic and the code you write looks minimalistic. Also, you can run Clojure code almost anywhere: as backend services, web frontends and even in shell scripts.

Even in Lambda functions?

I found out that it is not that difficult to make Clojure code to also run in AWS Lambda. The code can live in a Java runtime. Lambda events will be routed to a handler function written in Clojure, when the namespace implements a Java Request handler class (here's an example). Yes, there is some interop needed at the entry point of the Lambda code to make it work. But don't worry.

In addition to the Java interop, the source code should also be ahead-of-time compiled and packaged. I've used the uberdeps library that will make the process smooth when using tools.deps.

If you are not familiar with the Java lingo (like me, I have a background in Node.js, frontend and .NET), words like jar, AOT and even Java can be intimidating. I guess it is possible to sidestep all of this by writing the Lambda function in ClojureScript and run it in a Node.js runtime. But I don't want to opt out of the rich ecosystem of Clojure libraries built for the server side.

Sleepy lambda, slow cold starts

It seems that a Lambda running in a Java or .NET runtime often has painfully slow start up times. Setting a timeout of 3 seconds is probably not even enough. A simplistic solution to this problem is to use the AWS provisioned concurrency with a Lambda alias. No code changes required, only configuration and money. I wanted to find out if there are other ways to solve this problem.

What about GraalVM?

I found this great post about Clojure and Lambda written by Esko Luntola. Code that is compiled with GraalVM and running in Docker, solving the issues with slow cold starts and even makes requests in general super fast. Wow!

However, I haven't succeeded in going through the steps described in the post and am stuck in build failures that I don't know how to solve - yet. But I will try this approach some more. Even though it requires some initial setup with configs and Docker containers, this seems to be the way to go.

What about GraalVM in a custom runtime?

When digging deeper in how to run code in AWS Lambda, I found out that you can create your own runtime. To me, this approach looks simplistic and straight forward.

In this repo, I have written a Hello World example with:

  • a custom runtime (the file called bootstrap) written in bash (grabbed from the AWS Official docs with some additional error handling).
  • Clojure code, with a main function as the entry point. It is not neccessary to implement the Java Request handler class, and the main function returns data via standard output.

Input args as a JSON string

The Clojure code is compiled, and built with GraalVM by using the Native Image feature. Have a look at the Makefile for details.

compile and build with GraalVM Native Image
I've tried to keep things simple and followed the guides at clj-graal-docs and watched Michiel Borkents excellent beginners guide to GraalVM on YouTube.

The custom runtime and the function can be deployed separately. You can reuse the same runtime for several Lambda functions, by creating a Lambda Layer in AWS. The function code can be deployed directly, just upload the zipped file to AWS Lambda.

I like this approach, it works fine in my simplistic hello world example. But I haven't tried it in a real-world scenario. When going beyond an experiment, I think there might be additional resource configuration flags to Native Image required. Probably the setting ReflectionConfigurationFiles.

The tradeoffs?

From what I can see in my totally non-scientific weekend experimental testing is that the code running in my Custom Runtime has a cold start of somewhere between 100 and 300 milliseconds. Good enough. When warmed up, requests are processed between 15-30 milliseconds. Not bad.

When comparing with my other example lambda that is running in a Java runtime (with cold starts usually taking over 2000 milliseconds), the Custom Runtime with GraalVM is way faster.

But once warmed up, the Java runtime is actually super fast, with duration times between 1 - 30 milliseconds. Also, I haven't yet solved how to build all of this in a CI/CD setup. The code was built with GraalVM locally on my machine.

I would very much appreciate your input on the experiments shared in this blog post.

Photo by Abdelrahman Hassanein on Unsplash

lördag 27 februari 2021

Interactive Web Development

The workflow for developing web apps has been very much the same for quite some time, even if the tools have evolved and the programming languages have changed.

Write some code, save the file, switch to the browser window, hit the refresh button and wait.

Sometimes there has even been a couple of extra steps in between: write, save, compile, restart, switch to the browser, refresh, wait and repeat. The problem with this is that - at least for me - the focus on the actual problem to solve is paused or even worse: lost.

"Write code,
Switch to the browser window,
Hit the refresh button,
Wait ...
Now, where was I?"

But there’s hope!

🔥 Hot Reloading

With a modern development environment, you can use automation to get rid of some of the noice. Your code editor can probably be configured to detect when a file has changed and automatically save it.

With tools like Webpack for JavaScript and Shadow-cljs for ClojureScript, you can reload a running development web server - even replace code while the web server is running without loosing the current state. This is often called Hot Reloading and makes the development workflow a lot smoother than before. Very cool.

🧱 Building blocks

I really like the way React has solved problems with web development in general. React simplifies how you can separate features into components. At the same time, it promotes grouping relevant markup and code, by combining JavaScript & HTML into the JSX syntax. I think helps with keeping focus on the actual problem solving, with less navigating and flipping between files in the code editor. Good stuff.

♻️ The Virtual DOM

The Virtual DOM will give instant feedback when data has changed. The DOM is changed on the fly, without the need for page reloads or server side rendering. This is done by calculating the current state of the browser DOM and an in-memory copy of it. When there is a change in the copy, the relevant parts of the browser DOM will change. Really nice.

🦄 The Developer Superpower

Recently, I’ve learned about a really cool workflow called REPL Driven Development. I have used a REPL before, but have always thought of it as something that is used in a shell for some quick testing, not in the actual code editor. But with Clojure, this is the way we work. While you are in the editor, thinking, writing and looking at the code, you can evaluate it and get instant feedback. You can trigger events, browse state and even query the browser DOM! This is possible thanks to the Interactive REPL.

It’s almost like Magic. 🤩

I think this is unique to Clojure and ClojureScript. I’m not sure why this superpower doesn’t seem to exist elsewhere, but it probably has something to do with the structure of the language itself: code and data share structure and syntax.

✨This is Interactive Web Development

By combining hot reloading, building blocks & the virtual DOM with the Interactive REPL - we have something that I would like to call Interactive Web Development.

Arrange your code editor side-to-side with a browser window, to get instant feedback from both the user interface and the functionality when evaluating and experimenting with the code during development.

Photo at the top by Nong Vang on Unsplash

Have a look at my Func Prog Sweden second 2021 talk at YouTube that is covering this topic too. Direct link: ClojureScript: React with a Hiccup