7c7fcecd47
This also changes the structure of the object store, though the basic idea is the same. The object store contains a directory of objects, which are content addressable filesystem trees. Currently we only ever use their content-hash internally, but the idea for this is basically Lars Karlitski and Kay Sievers' `treesum()`. We may exopse this in the future. Moreover, it contains a directory of refs, which are symlinks named by the stage id they correspond to (as before), pointing to an object generated from that stage-id. The ObjectStore exposes three method: `has_tree()`: This checks if the content store contains the given tree. If so, we can rely on the tree remaining there. `get_tree()`: This is meant to be used with a `with` block and yields the path to a read-only instance of the tree with the given id. If the tree_id is passed in as None, an empty directory is given instead. `new_tree()`: This is meant to be used with a `with` block and yields the path to a directory in which the tree by the given id should be created. If a base_id is passed in, the tree is initialized with the tree with the given id. Only when the block is exited successfully is the tree written to the content store, referenced by the id in question. Use this in Pipeline.run() to avoid regenerating trees unneccessarily. In order to trigger a regeneration, the content store must currently be manually flushed. Update the travis test to run the noop pipeline twice, verifying that the stage is only run the first time. Signed-off-by: Tom Gundersen <teg@jklm.no>
89 lines
2.7 KiB
Markdown
89 lines
2.7 KiB
Markdown
# osbuild
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A build system for operating system images, working towards an image build
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pipeline that's more comprehensible, reproducible, and extendable.
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## Pipelines
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The build process for an image is described by a pipeline. Each
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[*stage*](/stages) in a pipeline is a program that, given some configuration,
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modifies a file system tree. Finally, an assembler takes a filesystem tree, and
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assembles it into an image. Pipelines are defined as JSON files like this one:
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```json
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{
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"name": "Example Image",
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"stages": [
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{
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"name": "org.osbuild.dnf",
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"options": {
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"releasever": "30",
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"repos": {
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"fedora": {
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"name": "Fedora",
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"metalink": "https://mirrors.fedoraproject.org/metalink?repo=fedora-$releasever&arch=$basearch",
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"gpgkey": "file:///etc/pki/rpm-gpg/RPM-GPG-KEY-fedora-$releasever-$basearch"
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}
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},
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"packages": [ "@Core", "grub2-pc", "httpd" ]
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}
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},
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{
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"name": "org.osbuild.systemd",
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"options": {
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"enabled_services": [ "httpd" ]
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}
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},
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{
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"name": "org.osbuild.grub2",
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"options": {
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"root_fs_uuid": "76a22bf4-f153-4541-b6c7-0332c0dfaeac"
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}
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}
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],
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"assembler": {
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"name": "io.weldr.qcow2",
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"options": {
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"filename": "example.qcow2",
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"root_fs_uuid": "76a22bf4-f153-4541-b6c7-0332c0dfaeac"
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}
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}
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}
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```
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`osbuild` runs each of the stages in turn, isolating them from the host and
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from each other, with the exception that they all operate on the same
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filesystem-tree. The assembler is similarly isolated, and given the same
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tree, in read-only mode and assembles it into an image without altering
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its contents.
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The filesystem tree produced by the final stage of a pipeline, is named
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and optionally saved to be reused as the base for future pipelines.
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Each stage is passed the (appended) `options` object as JSON over stdin.
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The above pipeline has no base and produces a qcow2 image.
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## Running
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```
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usage: python3 -m osbuild [-h] [--store DIRECTORY] [-l DIRECTORY] -o DIRECTORY
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PIPELINE
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Build operating system images
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positional arguments:
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PIPELINE json file containing the pipeline that should be built
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optional arguments:
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-h, --help show this help message and exit
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--store DIRECTORY the directory where intermediary os trees are stored
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-l DIRECTORY, --libdir DIRECTORY
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the directory containing stages, assemblers, and the
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osbuild library
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required named arguments:
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-o DIRECTORY, --output DIRECTORY
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provide the empty DIRECTORY as output argument to the
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last stage
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```
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