[tobbyb]

Layers are integral in Docker, layers were pushed as enabling reuse, composibility, 'immutability', every 'run' statement is a layer. They are not an implementation detail. Managing all these layers adds complexity and impact users from choosing storage drivers, to using layers to building images, and if you are going to use layers you need to be a privileged user to mount all these layers. [1]

Here is an example. I build an Nginx container with no layers from a base alpine image. Users can download and run it in a layer so the original Nginx container remains untouched or run a copy of it. If there is a security alert or update I rerun the build. No layers used. You build the same Nginx container will multiple layers, and have all the overhead of tracking and managing these layers. And users then download the Nginx container made up of all these layers and run it. If there is a security update in any lower layers it needs to rebuild. You have used a workflow and designed an entire system based on stacking layers to compose and build your image. That is a lot of overhead and complexity in basic image management. What is the benefit?

[1] https://kinvolk.io/blog/2018/04/towards-unprivileged-contain...

[cpuguy83]

Right, they are integral but the user doesn't interact with them and they can be swapped out for a different implementation and the user would never know outside of noticing the impact that the change has (or trade-offs such a change would make).

Caching for `docker build` really doesn't have anything to do with layers except as a means of storage, it doesn't need to be layers at all.

To be honest, layers aren't even all that efficient (except in perfectly ideal scenarios), just better than no sharing at all and no one has taken the time to come up with something better yet...because frankly there are many other things that need improvements before bothering with it.

Again, just figured I'd mention again... since you are trying to explain Docker to me... I'm a Docker maintainer and have been for the last ~5 years. Happy to chat about this.

[linuxftw]

Layers may or may not benefit any particular org. If you build a lot of your own containers from the same base layer image (microserver1-container-a .. microserver2-container-N), then you could save a lot of bandwidth/storage pulling the base layer once. Naturally, if you build everything from alpine:latest, then a large majority of your containers are going to have difference base layers and you're going to lose those savings.

[vetrom]

Similar to what linuxftw notes, when Docker hit the scene it was basically competing with the likes of Heroku where you have a few common runtime containers on a shared runtime system. When trying to implement one of those you want to maximize some sorts of shared common components and page/file sharing to create some efficiencies in memory sharing/oversubscription.