Container-only builds

It is possible to use Dalec when you wish to build a minimal image from scratch or based on one of Dalec's supported distros (see Targets for a list of these) with only certain packages installed. To do this, simply define a Dalec spec with only runtime dependencies specified. The resulting image will contain only the specified packages and their dependencies.

name: my-minimal-image
version: 0.1.0
description: A minimal distroless image with only curl and shell access
revision: 1

dependencies:
    runtime:
        curl:
        bash:

image:
    entrypoint: /bin/bash

Then, to build: docker buildx build -f my-minimal-image.yml --target=mariner2 -t my-minimal-image:0.1.0 .

This will produce a minimal image from scratch with curl, bash, and just a few other essential packages such as prebuilt-ca-certificates and tzdata.

How does this work? Dalec will create a Virtual Package which has only the specified runtime dependencies and install this in the target base image. This is where the --target=mariner2 flag comes in. Even though the resulting image is from scratch, it will have the specified packages installed from mariner2 repos.

note

Dalec needs to use the buildx cli in order to interact with a buildkit builder. In newer versions of docker, docker build is an alias for docker buildx build, and so the docker buildx command can be used interchangeably with docker build. However, if unsure or using an old version of docker, use docker buildx to ensure compatibility.