Custom images, all the way

Build from any Dockerfile: multi-stage, COPY --from, ARG, heredocs, ADD from a URL, FROM scratch and .dockerignore, with a build context of up to 100 MiB sent from a folder, where a rebuild uploads only what changed. Pull from private registries (Docker Hub, GitHub, Google, Amazon ECR and others) with credentials sealed on arrival and never returned. Each build of a name is its next version, tags such as latest point at versions, and a sandbox starts from name:tag. An image can run a start command and have its sandbox's create wait for a ready port or command. Rebuilds start from the steps an earlier build shares, four builds run at once on a paid account, and the build log streams. See custom images.