The Magical Power of NestJS

Today I wanted to make a quick post about a framework/toolset that I’ve become increasingly fond of – NestJS. For those not in the know, NestJS enables developers to write Express APIs (and more) in a very Angular-ish way, including coding in TypeScript.

NestJS - A progressive Node.js web framework

My adventures into NestJS began, as one could logically assume, with a need for a new API. Having been deeply submerged in Angular-land for several years now, NestJS looked like it was at least worth a peek – and after a peek, we decided it was a perfect fit and so we adopted it.

High-level, we needed an API to essentially wrap some node, npm and Angular CLI processes so that they could be interfaced with by clients via REST. All in all, the API writing process was very straight forward – a controller exposing our business concepts, which performed various node, npm, and Angular CLI operations via dedicated service implementations.

All in all, the writing experience was very pleasant with NestJS – but as often happens with enterprise projects, the target appeared to be moving pretty late in the game as requirements imposed by external players changed.

“Okay. Great. So now we have this REST API, but we’ve since decided that a CLI would be a better fit. Oh, and we needed it yesterday…”


If you’ve ever been a developer in a large organization, you know this sort of thing happens far more often than you’d generally prefer – but it’s life. Things change – lots of moving parts, lots of cooks in the kitchen, etc.

Behind schedule and over budget due to things that were outside of my control, I found myself considering a frantic rewrite of the API. Logically, my mind quickly moved to ‘how much of the API codebase can we leverage in our CLI’, as I opened up the NestJS docs in the hopes that I’d find my magical answer.

After a bit of hunting, I found ‘Application Context’: https://docs.nestjs.com/application-context

From the NestJS docs:

There are several ways of mounting the Nest application. You can create either a web app, microservice or just a Nest application context. Nest context is a wrapper around the Nest container, which holds all instantiated classes. We can grab an existing instance from within any imported module directly using application object. Hence, you can take advantage of the Nest framework everywhere, including CRON jobs and even build a CLI on top of it.

Perfect – this sounds to be just what the doctor ordered.

Having played with NestJS quite a bit, and being familiar with the transpilation process, I knew I’d essentially get a one-to-one output of my TS implementations in JS. Not wanting to change my API in a way that detracted from using the codebase as a REST API, I instead opted to add another entry point – adding ‘main.cli.ts’ alongside of the NestJS generated main.ts, in which I added my CLI specific logic.

Fortunately, having coded my API with abstractions / separation of concerns the best that I knew how, I had domain specific implementations wrapped in services rather than directly in controllers – this made my CLI experiment a dream rather than a nightmare. With just a few lines of new code in my main.cli, I was able to invoke my service logic from the command line – passing arguments at the CLI rather than properties in a POST body.

> node dist\main.cli.js --id 1

BOOM! DONE!

I honestly found myself blown away by the simplicity of this undertaking. Anxiously considering more or less a full rewrite initially, I found myself empowered by NestJS to fundamentally change my program, additively, in a matter of minutes – rather than the hours or days it would have required to do a full rewrite. With a dozen-or-so lines of new code, I now not only have a fully functional REST API, but I also have a CLI capable of doing the same things as the API.

Image result for magic gif


If you’ve not used NestJS before, I definitely recommend that you give it a look before you write your next API (or CLI)!
https://nestjs.com/
https://twitter.com/nestframework

-Matt


Playing with Docker on Windows 10 with Live Reload (nodemon)

Image result for what year is it

I know. I know. I’m a bit late to the game – and this was long overdue…

For a few years now, I’ve been fully submerged in the world of Enterprise Angular development – which has unfortunately led to me falling behind on some technologies, such as Docker. While I’ve been aware of LXCs for many, many years now, I’d not gotten past 101 setup tutorials for Docker to date – which changes today.

This post details my initial journey with running my first Docker container based Node.js application under Windows 10 – as well as the challenges encountered with live reload via nodemon during the journey, and how I got everything working well enough in the end.

As is often the case, I went looking for a recent basic getting started writeup, which led me to Dinushanka Ramawickrama’s “Let’s Dockerize a Nodejs Express API“. Being a huge fan of Node.js, often choosing it as my stack of preference, this seemed like a great place to start – taking a Node Express API and shoving it into a container using Docker.

All in all, I have to say that Dinushanka’s write up is pretty good – short, to the point, easy to follow, and accurate. It wasn’t until getting the last section, titled “Dynamically Change the Contents of the Running Container using Nodemon.”, that I ran into problems – for the life of me, I could not get live reload via nodemon to work as expected. Docker would output log messages seemingly indicating that all was well, but when I’d make changes to my server they weren’t syncing in my Docker container.

nodemon reporting for duty – but the duty never shows

As I often do in situations like this, I turned to the comments – assuming that someone else had already experienced my pain and provided me a nicely packaged solution. Nope – not this time. So I went searching, which led me to a relatively recent issue on nodemon’s github repo:
https://github.com/remy/nodemon/issues/1447 . As suggested by a commenter, I checked out “Application isn’t restarting” in the nodemon readme –
https://github.com/remy/nodemon#application-isnt-restarting . Going for the low hanging fruit approach, I updated my package.json’s dev script to include the Legacy Watch flag:


Now, all that was left was to rebuild my image and rerun it:

> docker-compose down
> docker-compose build
> docker-compose up

With the above in place, all was well in the world – containerized live reloading node development. AIN’T LIFE GRAND?!

Long story short, essentially the mechanisms leveraged on Linux systems to detect filesystem changes aren’t available in Windows – and so live reload doesn’t work out of the box. Fortunately, nodemon’s Legacy Watch uses a different (though more costly) polling mechanism to detect changes – which works fine for our purposes of ‘getting started’. Note: this is actually a known issue, as you can see in the Docker official docs:
https://docs.docker.com/docker-for-windows/troubleshoot/#inotify-on-shared-drives-does-not-work

It’s worth mentioning that some folks have reported this issue when developing on host Linux systems, which is believed to be related to inotify-tools not being present in the OS image used to create your container. In these cases, your nodemon woes may be solved by simply updating your Dockerfile with an additional run statement to install the package using the container OS’ package manager. See here:
https://stackoverflow.com/questions/42445288/enabling-webpack-hot-reload-in-a-docker-application/46804953#46804953

-Matt