# Alpine Linux Cloud Image Builder

This repository contains the code and and configs for the build system used to
create official Alpine Linux images for various cloud providers, in various
configurations.  This build system is flexible, enabling others to build their
own customized images.

----
## Pre-Built Offical Cloud Images

To get started with offical pre-built Alpine Linux cloud images, visit
https://alpinelinux.org/cloud.  Currently, we build official images for the
following cloud platforms...
* AWS

...we are working on also publishing offical images to other major cloud
providers.

Each published image's name contains the Alpine version release, architecture,
firmware, bootstrap, and image revision.  These details (and more) are also
tagged on the images...

| Tag | Description / Values |
|-----|----------------------|
| name | `alpine-`_`release`_`-`_`arch`_`-`_`firmware`_`-`_`bootstrap`_`-r`_`revision`_ |
| project | `https://alpinelinux.org/cloud` |
| image_key | _`release`_`-`_`arch`_`-`_`firmware`_`-`_`bootstrap`_`-`_`cloud`_ |
| version | Alpine version (_`x.y`_ or `edge`) |
| release | Alpine release (_`x.y.z`_ or _`YYYYMMDD`_ for edge) |
| arch | architecture (`aarch64` or `x86_64`) |
| firmware | boot mode (`bios` or `uefi`) |
| bootstrap | initial bootstrap system (`tiny` = Tiny Cloud) |
| cloud | provider short name (`aws`) |
| revision | image revision number |
| imported | image import timestamp |
| import_id | imported image id |
| import_region | imported image region |
| published | image publication timestamp |
| description | image description |

Although AWS does not allow cross-account filtering by tags, the image name can
still be used to filter images.  For example, to get a list of available Alpine
3.x aarch64 images in AWS eu-west-2...
```
aws ec2 describe-images \
  --region eu-west-2 \
  --owners 538276064493 \
  --filters \
    Name=name,Values='alpine-3.*-aarch64-*' \
    Name=state,Values=available \
  --output text \
  --query 'reverse(sort_by(Images, &CreationDate))[].[ImageId,Name,CreationDate]'
```
To get just the most recent matching image, use...
```
  --query 'max_by(Image, &CreationDate).[ImageId,Name,CreationDate]'
```

----
## Build System

The build system consists of a number of components:

* the primary `build` script
* the `configs/` directory, defining the set of images to be built
* the `scripts/` directory, containing scripts and related data used to set up
  image contents during provisioning
* the Packer `alpine.pkr.hcl`, which orchestrates build, import, and publishing
  of images
* the `cloud_helper.py` script that Packer runs in order to do cloud-specific
  import and publish operations

### Build Requirements
* [Python](https://python.org) (3.9.7 is known to work)
* [Packer](https://packer.io) (1.7.6 is known to work)
* [QEMU](https://www.qemu.org) (6.1.0 is known to work)
* cloud provider account(s)

### Cloud Credentials

By default, the build system relies on the cloud providers' Python API
libraries to find and use the necessary credentials, usually via configuration
under the user's home directory (i.e. `~/.aws/`, `~/.oci/`, etc.) or or via
environment variables (i.e. `AWS_...`, `OCI_...`, etc.)

The credentials' user/role needs sufficient permission to query, import, and
publish images -- the exact details will vary from cloud to cloud.  _It is
recommended that only the minimum required permissions are granted._

_We manage the credentials for publishing official Alpine images with an
"identity broker" service, and retrieve those credentials via the
`--use-broker` argument of the `build` script._

### The `build` Script

```
usage: build [-h] [--debug] [--clean] [--pad-uefi-bin-arch ARCH [ARCH ...]]
         [--custom DIR [DIR ...]] [--skip KEY [KEY ...]] [--only KEY [KEY ...]]
         [--revise] [--use-broker] [--no-color] [--parallel N]
         [--vars FILE [FILE ...]]
         {configs,state,rollback,local,upload,import,publish,release}

positional arguments:   (build up to and including this step)
  configs   resolve image build configuration
  state     refresh current image build state
  rollback  remove existing local/uploaded/imported images if un-published/released
  local     build images locally
  upload    upload images and metadata to storage
* import    import local images to cloud provider default region (*)
* publish   set image permissions and publish to cloud regions (*)
  release   mark images as being officially relased

(*) may not apply to or be implemented for all cloud providers

optional arguments:
  -h, --help              show this help message and exit
  --debug                 enable debug output
  --clean                 start with a clean work environment
  --pad-uefi-bin-arch ARCH [ARCH ...]
                          pad out UEFI firmware to 64 MiB ('aarch64')
  --custom DIR [DIR ...]  overlay custom directory in work environment
  --skip KEY [KEY ...]    skip variants with dimension key(s)
  --only KEY [KEY ...]    only variants with dimension key(s)
  --revise                remove existing local/uploaded/imported images if
                          un-published/released, or bump revision and rebuild
  --use-broker            use the identity broker to get credentials
  --no-color              turn off Packer color output
  --parallel N            build N images in parallel
  --vars FILE [FILE ...]  supply Packer with -vars-file(s) (default: [])
```

The `build` script will automatically create a `work/` directory containing a
Python virtual environment if one does not already exist.  This directory also
hosts other data related to building images.  The `--clean` argument will
remove everything in the `work/` directory except for things related to the
Python virtual environment.

If `work/configs/` or `work/scripts/` directories do not yet exist, they will
be populated with the base configuration and scripts from `configs/` and/or
`scripts/` directories.  If any custom overlay directories are specified with
the `--custom` argument, their `configs/` and `scripts/` subdirectories are
also added to `work/configs/` and `work/scripts/`.

The "build step" positional argument deterimines the last step the `build`
script should execute -- all steps before this targeted step may also be
executed.  That is, `build local` will first execute the `configs` step (if
necessary) and then the `state` step (always) before proceeding to the `local`
step.

The `configs` step resolves configuration for all buildable images, and writes
it to `work/images.yaml`, if it does not already exist.

The `state` step always checks the current state of the image builds,
determines what actions need to be taken, and updates `work/images.yaml`.  A
subset of image builds can be targeted by using the `--skip` and `--only`
arguments.

The `rollback` step, when used with `--revise` argument indicates that any
_unpublished_ and _unreleased_ local, imported, or uploaded images should be
removed and rebuilt.

As _published_ and _released_ images can't be removed, `--revise` can be used
with `configs` or `state` to increment the _`revision`_ value to rebuild newly
revised images.

`local`, `upload`, `import`, `publish`, and `release` steps are orchestrated by
Packer.  By default, each image will be processed serially; providing the
`--parallel` argument with a value greater than 1 will parallelize operations.
The degree to which you can parallelze `local` image builds will depend on the
local build hardware -- as QEMU virtual machines are launched for each image
being built.  Image `upload`, `import`, `publish`, and `release` steps are much
more lightweight, and can support higher parallelism.

The `local` step builds local images with QEMU, for those that are not already
built locally or have already been imported.  Images are converted to formats
amenable for import into the cloud provider (if necessary) and checksums are
generated.

The `upload` step uploads the local image, checksum, and metadata to the
defined `storage_url`.  The `import`, `publish`, and `release` steps will
also upload updated image metadata.

The `import` step imports the local images into the cloud providers' default
regions, unless they've already been imported.  At this point the images are
not available publicly, allowing for additional testing prior to publishing.

The `publish` step copies the image from the default region to other regions,
if they haven't already been copied there.  This step will always update
image permissions, descriptions, tags, and deprecation date (if applicable)
in all regions where the image has been published.

***NOTE:***  The `import` and `publish` steps are skipped for those cloud
providers where this does not make sense (i.e.  NoCloud) or for those which
it has not yet been coded.

The `release` step marks the images as being fully released.

### The `cloud_helper.py` Script

This script is meant to be called only by Packer from its `post-processor`
block.

----
## Build Configuration

For more in-depth information about how the build system configuration works,
how to create custom config overlays, and details about individual config
settings, see [CONFIGURATION.md](CONFIGURATION.md).