Introduce image-gen subcommand for airshipctl
Change-Id: Ic5e5a3619c574014ce2b32dccb97abbbacbcb270
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Dmitry Ukov
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specs/approved/airshictl_bootstrap_image.rst
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specs/approved/airshictl_bootstrap_image.rst
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..
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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.. index::
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single: airshipctl
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single: bootstrap
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single: ISO
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single: image
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single: CLI
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====================================
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Airshipctl Bootstrap Image Generator
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====================================
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This spec defines new ``isogen`` sub-command for ``airshipctl bootstrap``
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and describes interface for image builder. Airship CLI tool will be extended
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with an ability to generate ISO image or image for USB stick. This image can be
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used to boot up ephemeral node with Kubernetes cluster installed
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Links
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=====
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Jira tasks:
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- `LiveCD PoC <https://airship.atlassian.net/browse/AIR-132>`_
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Problem description
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===================
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Common approach for spinning new Kubernetes cluster is Cluster API deployed
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on top of small single node cluster based on ``kind`` or ``minikube``. In order
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to create Kubernetes cluster on hardware nodes in Data Center user have to
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deploy this single node cluster on virtual machine attached to PXE network or to
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deploy operating system and Kubernetes cluster to one of the hardware servers.
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In scope of Airship 2.0 user needs to be able to bootstrap ephemeral Kubernetes
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cluster with minimal required services (e.g. Cluster API, Metal3, etc).
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Ephemeral Cluster should be deployed remotely (if possible) and deployment process
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needs to be fully automated.
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Impacted components
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===================
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- airshipctl
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Proposed change
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===============
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Airship 2.0 command line tool (i.e. ``airshipctl``) will be able to perform
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full cycle of bootstrapping ephemeral Kubernetes node.
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First bootstrap step is to generate ISO or flash drive image. Image generator
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is executed inside of a container and returns LiveCD or LiveUSB image.
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Image generator must implement interface defined below (see
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'Image Generator Container Interface' section) since ``isogen``
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command treats image generator container as a black box.
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Airshipct subcommand
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--------------------
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``airshipctl bootstrap`` is extended with ``isogen`` subcommand.
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Subcommand is extendable by adding Container Runtime Environment drivers.
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Following subcommand flags are available:
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- ``-c`` or ``--cre`` Container Runtime Environment driver (default: docker)
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- ``-i`` or ``--image`` Image generator container image URL
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- ``-v`` or ``--volume`` Volume mount for artifacts (coud-init and output
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image). Example ``-v /source/path/on/host:/dst/path/in/container``
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Subcommand should implement following steps:
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- Utilize the ``airshipctl config`` to identify the location of YAML documents
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that describe the intention for the site
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- Identify the YAML files that describe the details required for the HOST for
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which the ISO is been generated.
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- Extract from the appropriate YAML(s) the information for the HOST, such as
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IP, Name, MAC, etc.
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- Gather the information from the YAML and generate the appropriate
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cloud-config.yaml file.
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YAML manipulations described above rely on functions and methods that
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have been implemented as a part of ``airshipctl document`` command.
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Image Generator Container Interface
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-----------------------------------
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Image generator container input.
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- Volume (host directory) mounted to certain directory in container. Source
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and target directories for binding can be placed anywhere. Target directory
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path depends on particular image builder implementation. Example:
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``docker run -v /source/path/on/host:/dst/path/in/container ...``
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- Cloud-init configuration file named ``cloud-config.yaml`` placed in the root of
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the volume
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Image generator output.
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- YAML-formatted metadata which describes output artifacts. Metadata must
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satisfy following schema
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.. code-block::
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$schema: 'http://json-schema.org/schema#'
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type: 'object'
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properties:
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image_type:
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type: 'string'
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description: 'Type of generated image (iso or image for USB stick)'
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enum:
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- 'iso'
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- 'img'
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image_location:
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type: 'string'
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description: 'Image file location'
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k8s_client_config:
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type: 'string'
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description: 'Path to Kubernetes client config'
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- ISO or flash disk image placed in root of the mounted volume
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- Configuration file (with certificates) for Kubernetes client (i.e ``kubectl``)
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Security impact
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---------------
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- Certificates for ephemeral Kubernetes cluster are generated dynamically
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during ISO generation procedure. These certificates must be temporary
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and should differ from production Kubernetes cluster.
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- Certificates are saved on the ISO along with other Cloud Init data
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- Configuration file for Kubernetes client is saved locally (on a machine
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where ``airshipctl`` has been executed)
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Performance impact
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------------------
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None
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Alternatives
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------------
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- Modify existing LiveCD ISO image.
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- Requires implementation of ISO modification module in Golang.
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- Support multiple operating systems is challenging since there is no
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standard for ISO image directory structure and live booting
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Implementation
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==============
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- Image Generator reference implementation based on Debian container
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- Dockerfile with all packages required to build LiveCD ISO
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- Builder script
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- ``airshipctl bootstrap`` extension with new command (i.e.
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``airshipctl bootstrap isogen``)
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- Define interface for running container execution which enables following
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methods
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- Pull image: download container image if it's not presented locally
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- Run container: start container, wait for builder script is finished,
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output builder log if CLI debug flag is enabled
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- Implement interface for docker Container Runtime Environment
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Dependencies
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============
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- New version of hardware nodes definition format in Treasuremap since
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Metal3-IO will replace MAAS for Airship 2.0
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References
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==========
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None
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