Building slim containers: When less is more – and when it isn’t

When it comes to containers, it’s often believed that less is more. Slim containers  –  minimal Docker images built with only the essentials  –  promise faster build times, lower cloud costs, and a smaller attack surface for vulnerabilities. In essence, the leaner the container, the better the performance and the stronger the security  –  or so the thinking goes.

But like most things in tech, the reality is a little more complicated. In this post, we'll unpack both the advantages and the trade-offs of slimming down your containers  –  and why sometimes "just enough" is actually too little.

Alpine & Distroless: The champions of slim containers

Today, the most widely used slim images are Alpine-based containers. Alpine is inherently lightweight, including only the essential packages needed to run applications. It replaces heavier GNU components with smaller, faster alternatives  –  for example, it uses musl instead of glibc, and BusyBox instead of coreutils. As a result, Alpine-based containers often weigh in at just a few megabytes, making them a go-to option for teams looking to cut image size without sacrificing too much flexibility.

And for those looking for even more minimalism, there’s Distroless. Distroless images take the slim container concept to an extreme by including only an application and its runtime dependencies, with no package manager, no shell access, and no full operating system – hence the name “distroless.”

The problem with slim containers?

While the radical simplicity of distroless eliminates many potential security vulnerabilities and reduces bloat even more than Alpine, the trade-off is a container that's harder to inspect, debug, and modify after it's built. On top of that, Distroless images are only available in a handful of flavors, so if your application doesn’t run with one of the supported runtimes, you’re left building your own image from scratch.

And despite its lightweight appeal, Alpine still has some notable limitations as well, which are not to be understated. Its use of ash, the default POSIX-compliant shell provided by BusyBox, lacks many of the features available in more common shells like bash or zsh. Since most modern scripts - whether in GitHub workflows or custom developer scripts - assume a bash environment, running them under ash can trigger significant compatibility problems.

A deeper and arguably more significant limitation of Alpine comes from its use of musl as its standard C library, instead of the more common glibc. Due to musl being lighter and simpler by design, it omits certain features and extensions that glibc provides. This can lead to both compatibility and performance issues. For example, major runtimes like Node.js don’t officially support musl, which can cause subtle behavior differences or even break native modules and add-ons.

Where workarounds fall short

While there are some ways to mitigate these issues, they often come at the cost of convenience  –  or wind up undermining the benefits of using a slim image in the first place.

Distroless images, for instance, offer a debug variant that includes a shell, which can make debugging a bit more manageable. However, these debug images still lack a package manager, so you can’t install missing tools or dependencies.

Alpine offers slightly greater flexibility, with the ability to install ports of bash, glibc, and other familiar utilities, but doing so essentially turns the image into a more typical Linux distribution – negating most of its size and performance advantages. In practice, these fixes often introduce complexity without resolving the underlying compatibility gaps. As a result, enterprise-grade base images, which strip away unnecessary components while still offering the full spectrum of features, may be the more strategic choice in many situations.

So… When is slim actually better?

The industry is clearly moving toward faster, slimmer, and more secure containers given that they reduce image size, limit security exposure, and cut down on unnecessary bloat. But they aren’t a universal fit. The trade-offs in compatibility, flexibility, and debugging can sometimes outweigh the benefits, especially at scale or in complex environments.

For small, self-contained workloads with minimal external dependencies, Alpine or Distroless might be exactly what you need. But for teams in need of more visibility, predictability, or runtime compatibility, enterprise-grade base images can offer a more balanced foundation.