Hands-on · 9 missions · runs in your browser
A small simulated builder that follows BuildKit's real rules: cache keys, .dockerignore, multi-stage graphs, cache mounts, layer pushes and container layers. Edit the files, press Build, and watch what reruns. Every mission ends with the command that shows the same thing on your real Docker.
| # | context | steps run / cached | time | image |
|---|
| tag | points at |
|---|---|
| nothing pushed yet | |
The rules are real: a step's cache key is its parent's key plus the instruction plus, for COPY, the checksums of the copied files. One miss reruns everything after it. Stages that the target doesn't need are skipped. Cache mounts persist across builds and prune. Pushes upload only missing blobs. The numbers are made up but realistic: download and install times, and image sizes. To see real ones, run the examples next to this page:
cd ~/Desktop/Claude/containers-in-3d/examples
./try.sh # all five experiments
./try.sh cache # or one: layers | cache | multistage | cachemount | devcontainer