# image-template

# Purpose

This repository is meant to be a template for building your own custom Universal Blue image. This template is the recommended way to make customizations to any image published by the Universal Blue Project:
- [Aurora](https://getaurora.dev/)
- [Bazzite](https://bazzite.gg/)
- [Bluefin](https://projectbluefin.io/)
- [uCore](https://projectucore.io/)
- [main](https://github.com/ublue-os/main/)
- [hwe](https://github.com/ublue-os/hwe/)

or any other base image:

- CentOS Stream 9: `quay.io/centos-bootc/centos-bootc:stream9`
- CentOS Stream 10 (in development): `quay.io/centos-bootc/centos-bootc:stream10`
- Fedora: `quay.io/fedora/fedora-bootc:41`

This template includes a Containerfile and a Github workflow for building the container image, signing, and proper metadata to be listed on [artifacthub](https://artifacthub.io/). As soon as the workflow is enabled in your repository, it will build the container image and push it to the Github Container Registry.

# Prerequisites

Working knowledge in the following topics:

- Containers
  - https://www.youtube.com/watch?v=SnSH8Ht3MIc
  - https://www.mankier.com/5/Containerfile
- bootc
  - https://containers.github.io/bootc/
- Fedora Silverblue (and other Fedora Atomic variants)
  - https://docs.fedoraproject.org/en-US/fedora-silverblue/
- Github Workflows
  - https://docs.github.com/en/actions/using-workflows

# How to Use

## Template

Select `Use this Template` and create a new repository from it. To enable the workflows, you may need to go the `Actions` tab of the new repository and click to enable workflows.

## Containerfile

This file defines the operations used to customize the selected image. It contains examples of possible modifications, including how to:
- change the upstream from which the custom image is derived
- add additional RPM packages
- add binaries as a layer from other images

## Building an ISO

Modify `iso.toml` to point to your custom image before generating an ISO.

- (Steps in progress)

## Workflows

### build.yml

This workflow creates your custom OCI image and publishes it to the Github Container Registry (GHCR). By default, the image name will match the Github repository name.

#### Container Signing

Container signing is important for end-user security and is enabled on all Universal Blue images. It is recommended you set this up, and by default the image builds *will fail* if you don't.

This provides users a method of verifying the image.

1. Install the [cosign CLI tool](https://edu.chainguard.dev/open-source/sigstore/cosign/how-to-install-cosign/#installing-cosign-with-the-cosign-binary)

2. Run inside your repo folder:

    ```bash
    cosign generate-key-pair
    ```

    
    - Do NOT put in a password when it asks you to, just press enter. The signing key will be used in GitHub Actions and will not work if it is encrypted.

> [!WARNING]
> Be careful to *never* accidentally commit `cosign.key` into your git repo.

3. Add the private key to GitHub

    - This can also be done manually. Go to your repository settings, under Secrets and Variables -> Actions
    ![image](https://user-images.githubusercontent.com/1264109/216735595-0ecf1b66-b9ee-439e-87d7-c8cc43c2110a.png)
    Add a new secret and name it `SIGNING_SECRET`, then paste the contents of `cosign.key` into the secret and save it. Make sure it's the .key file and not the .pub file. Once done, it should look like this:
    ![image](https://user-images.githubusercontent.com/1264109/216735690-2d19271f-cee2-45ac-a039-23e6a4c16b34.png)

    - (CLI instructions) If you have the `github-cli` installed, run:

    ```bash
    gh secret set SIGNING_SECRET < cosign.key
    ```

4. Commit the `cosign.pub` file to the root of your git repository.

# Community

- [**bootc discussion forums**](https://github.com/containers/bootc/discussions) - Nothing in this template is ublue specific, the upstream bootc project has a discussions forum where custom image builders can hang out and ask questions.
- Index your image on [artifacthub.io](https://artifacthub.io), use the `artifacthub-repo.yml` file at the root to verify yourself as the publisher. 

## Community Examples

- [m2os](https://github.com/m2giles/m2os)
- [bos](https://github.com/bsherman/bos)
- [homer](https://github.com/bketelsen/homer/)