How to build smaller Docker images

When you’re building a Docker image it’s important to keep the size under control. Having small images means ensuring faster deployment and transfers.

Wish I had found this post before I started playing with Docker, as it is packed with solid advice which I found out “along the way” myself.

In short:

  1. Find the right balance with the cache layers
  2. Use .dockerignore files
  3. Use the multi-stage builds feature
  4. Choose the right base image

Especially number 3 was an eye opener to me when I first discovered it. Basically it boils down to this: Don’t do an npm install/composer install/npm build directly in your “main” image, but do it in a separate container and afterwards copy its results into your main image.

How to build a smaller Docker image →

Automatically compress images to your Pull Requests with this GitHub Action

The folks at Calibre have release a GitHub Action named “Image Actions” and I must say, it looks amazing insane:

Image actions will automatically compress jpeg and png images in GitHub Pull Requests.

  • Compression is fast, efficient and lossless
  • Uses mozjpeg + libvips, the best image compression available
  • Runs in GitHub Actions, so it’s visible to everyone

Never ship unoptimised graphics again!

Once the workflow is added to your repo, Compression levels and source paths exclusions can easily be configured using a .github/calibre/image-actions.yml file:

  quality: 80
  quality: 80
  - "node_modules/**"

Calibre Blog: Automatically compress images on Pull Requests →
GitHub Actions Marketplace: Image actions →

🤔 In case you’re wondering why you should compress your images be sure to read Addy Osmani’s free ebook “Essential Image Optimization”

How Web Content Can Affect Power Usage

The Webkit blog, on how to optimize your pages so that they don’t drain the battery of your visitors their devices:

Users spend a large proportion of their online time on mobile devices, and a significant fraction of the rest is users on untethered laptop computers. For both, battery life is critical. In this post, we’ll talk about factors that affect battery life, and how you, as a web developer, can make your pages more power efficient so that users can spend more time engaged with your content.

The three sections where to optimize covered are scripting, painting (the way stuff is rendered/animated), and networking (requests over the network)

How Web Content Can Affect Power Usage →

Essential Image Optimization

Essential Image Optimization is an free and online eBook by Addy Osmani:

Images take up massive amounts of internet bandwidth because they often have large file sizes. According to the HTTP Archive, 60% of the data transferred to fetch a web page is images composed of JPEGs, PNGs and GIFs. As of July 2017, images accounted for 1.7MB of the content loaded for the 3.0MB average site.

Per Tammy Everts, adding images to a page or making existing images larger have been proven to increase conversion rates. It’s unlikely that images will go away and so investing in an efficient compression strategy to minimize bloat becomes important.

Essentially Addy pushes forward two key factors:

  1. We should all be automating our image compression
  2. Everyone should be compressing their images efficiently

Essential Image Optimization →

Flipboard Engineering: 60fps on the mobile web


Since earlier this week Flipboard now is a website too. As they wanted to mimic their mobile apps, it would sport lots of animations. During their first tests, they found the DOM being too slow (although that’s not entirely true, see this video and its description for example). And then, an epiphany:

Most modern mobile devices have hardware-accelerated canvas, so why couldn’t we take advantage of this? HTML5 games certainly do. But could we really develop an application user interface in canvas?

And so they did. They’ve built react-canvas for this, “high performance <canvas> rendering for React components”. Reminds me of Letterpress, which is an optimized OpenGL scene, and, which is a WebGL layer which renders the site.

60fps on the mobile web — Flipboard Engineering →
react-canvas →

Supercharging your Gruntfile

In this article, we won’t focus on what numerous Grunt plugins do to your actual project code, but on the Grunt build process itself. We will give you practical ideas on:

  • How to keep your Gruntfile neat and tidy,
  • How to dramatically improve your build time,
  • And how to be notified when a build happens.

Supercharging your Gruntfile →

Tools for image optimization

Where possible, it’s best to try automating image optimization so that it’s a first-class citizen in your build chain. To help, I thought I’d share some of the tools I use for this.

Not only contains a list of grunt plugins one can use, but also a few command line and online tools. I’ve been using TinyPNG for quite some time now before uploading images to my blog. Can shave up to 83% (!) of a screenshot created in OS X.

Tools for image optimization →

One Less JPG

Update 2017: By now it’s clear that an equal amount of JS-bytes and JPG-bytes are not the same. The JS still needs to be evaluated and executed, which also comes as a cost.

People often build beautiful sites with multiple easy-to-use JavaScript libraries. Then, when it comes to addressing frontend performance, suddenly those libraries are an enormous download that the users are forced to bear.

Before you go worrying about how to minify every last library or shave tests out of Modernizr, try and see if you can remove just one photo from your design. It will make a bigger difference.

One Less JPG →