Virtual Packages

In this section, we'll go over how to build virtual packages with Dalec. Virtual packages are packages that don't install any files themselves but instead reference other packages as dependencies. They are useful for creating a package that is just a collection of dependencies.

In this example, we'll build a virtual package that just installs other packages as dependencies.

# syntax=ghcr.io/azure/dalec/frontend:latest
name: my-package
version: 1.0.0
revision: "1"
packager: Contoso
vendor: Contoso
license: MIT
description: A virtual package that, when installed, triggers other packages to be installed
website: http://contoso.com

dependencies:
  runtime:
    - my-package-foo
    - my-package-bar

You can build it with:

docker build -t my-package-image:1.0.0 --target=mariner2 -f my-package.yml .

note

The syntax line tells docker the parser to use so it can understand the dalec spec format. Having # syntax=ghcr.io/azure/dalec/frontend:latest is required at the top of the Dalec spec file.

tip

You could also pass the dalec spec file via stdin docker build -t my-package-image:1.0.0 -< my-package.yml* See docker's documentation for more details on how you can pass the spec file to docker.

This will produce a container image named my-package-image:1.0.0 that has the my-package virtual package installed along with its runtime dependencies. By default, the produced container image is a scratch container image that only contains the package and its dependencies. You can customize the base image to use for the prooduced container. Below is an example that uses the Azure Linux core image as the base image which includes a shell and other tools.

# syntax=ghcr.io/azure/dalec/frontend:latest
name: my-package
version: 1.0.0
revision: "1"
packager: Contoso
vendor: Contoso
license: MIT
description: A virtual package that, when installed, triggers other packages to be installed
website: http://contoso.com

dependencies:
  runtime:
    - my-package-foo
    - my-package-bar

targets:
  mariner2:
    image:
      base: mcr.microsoft.com/cbl-mariner/base/core:2.0

You can also set other image settings like entrypoint/cmd, environment variables, working directory, labels, and more. Below is an example that sets the entrypoint to /bin/sh -c.

# syntax=ghcr.io/azure/dalec/frontend:latest
name: my-package
version: 1.0.0
packager: Contoso
vendor: Contoso
license: MIT
description: A virtual package that, when installed, triggers other packages to be installed
website: http://contoso.com

dependencies:
  runtime:
    - my-package-foo
    - my-package-bar

image:
    entrypoint: /bin/sh -c

Note how this is at the top level of the spec and not under a build target. This means that it applies to all targets, but can also be customized per target by adding it under a target.

targets:
  mariner2:
    image:
      entrypoint: /bin/sh -c