Image building tools for Openstack

These tools are the components of tripleo (https://github.com/tripleo/demo) that do the plumbing involved in building disk images. Specific configs live in the demo repository, while the reusable tools live here.

What tools are there?

• disk-image-create -o filename {flavour} [{flavour} ...] : Create an image of flavour {flavour}, optionally mixing in other flavours.

• ramdisk-image-create -o filename {flavour} [{flavour} ...] : Create a kernel+ ramdisk pair for running maintenance on bare metal machines (deployment, inventory, burnin etc).

  ramdisk-image-create -o deploy.ramdisk deploy

• disk-image-get-kernel filename : Extract the appropriate kernel and ramdisk to use when doing PXE boot using filename as the image for a machine.

• flavours can be found in the top level flavours directory.

Why?

Automation: While users and operators can manually script or put together ram disks and disk images, mature automation makes customisation and testing easier.

Design

Images are built using a chroot and bind mounted /proc /sys and /dev. The goal of the image building process is to produce blank slate machines that have all the necessary bits to fulfill a specific purpose in the running of an Openstack cloud: e.g. a nova-compute node.

A flavour is a particular set of code that alters how the image is built, or runs within the chroot to prepare the image. E.g. the local-config flavour copies in the http proxy and ssh keys of the user running the image build process into the image, whereas the vm flavour makes the image build a regular VM image with partition table and installed grub boot sector. The mellanox flavour adds support for mellanox infiniband hardware to both the deploy ramdisk and the built images.

Images start as a base ubuntu cloud image. Other distributions may be added in future, the infrastructure deliberately makes few assumptions about the exact operating system is use. The base image has opensshd running (a new key generated on first boot) and accepts use keys via the cloud metadata service, loading them into the 'ubuntu' user.

The goal of a built image is to have any global configuration ready to roll, but nothing that ties it to a specific cloud instance: images should be able to be dropped into a test cloud and validated, and then deployed into a production cloud (usually via bare metal nova) for production use. As such, the image contents can be modelled as three distinct portions:

• global content: the actual code, kernel, always-applicable config (like disabling password authentication to sshd).
• metadata / config management provided configuration: user ssh keys, network address and routes, configuration management server location and public key, credentials to access other servers in the cloud. These are typically refreshed on every boot.
• persistent state: sshd server key, database contents, swift storage areas, nova instance disk images, disk image cache. These would typically be stored on a dedicated partition and not overwritten when re-deploying the image.

The goal of the image building tools is to create machine images that content the correct global content and are ready for 'last-mile' configuration by the nova metadata API, after which a configuration management system can take over (until the next deploy, when it all starts over from scratch).

Existing flavours

Flavours are found in the subdirectory flavours. Each flavour is in a directory named after the flavour itself. Flavours should have a README.md in the root of the flavour directory describing what it is for.

Writing a flavour

Make as many of the following subdirectories as you need, depending on what part of the process you need to customise:

• block-device-size.d: Alter the size (in GB) of the disk image. This is useful when a particular flavour will require a certain minimum (or maximum) size. You can either error and stop the build, or adjust the size to match. NB: Due to the current simple implementation, the last output value wins so this should be used rarely - only one flavour in a mix can reliably set a size.

• outputs: $IMAGE_SIZE={size_in_GB}

• inputs: $IMAGE_SIZE={size_in_GB}

• block-device.d: customise the block device that the image will be made on (e.g. to make partitions).

• outputs: $IMAGE_BLOCK_DEVICE={path}

• inputs: $IMAGE_BLOCK_DEVICE={path}

• extra-data.d: pull in extra data from the host environment that hooks may need during image creation. This should copy any data (such as SSH keys, http proxy settings and the like) somewhere under $TMP_HOOKS_PATH.

• outputs: None

• inputs: $TMP_HOOKS_PATH

• pre-install.d: Run code in the chroot before customisation or packages are installed. A good place to add apt repositories.

• install.d: Runs after pre-install.d in the chroot. This is a good place to install packages, chain into configuration management tools or do other image specific operations.

• first-boot.d: Runs inside the image before rc.local. Scripts from here are good for doing per-instance configuration based on cloud metadata.

Ramdisk flavours support the following files in their flavour directories:

• binary-deps : executables required to be fed into the ramdisk. These need to be present in your $PATH.

• init : a POSIX shell script fragment that will be appended to the default script executed as the ramdisk is booted (/init)

Third party flavours

Pending implementation. The idea is to have a search path for flavours.

Installation

• Clone the repository locally, then add bin to your path.

• Copy sudoers.d/* into your /etc/sudoers.d/. (Warning, use visudo -c -f {filename} to check that each one parses successfully on your machine, so you don't break your machine).

Invocation

The scripts can generally just be run. Options can be set on the command line or by exporting variables to override those present in lib/img-defaults. -h to get help.