How bootstrap-vz works¶
At its core bootstrap-vz is based on tasks that perform units of work. By keeping those tasks small and with a solid structure built around them a high degree of flexibility can be achieved. To ensure that tasks are executed in the right order, each task is placed in a dependency graph where directed edges dictate precedence. Each task is a simple class that defines its predecessor tasks and successor tasks via attributes. Here is an example:
class MapPartitions(Task): description = 'Mapping volume partitions' phase = phases.volume_preparation predecessors = [PartitionVolume] successors = [filesystem.Format] @classmethod def run(cls, info): info.volume.partition_map.map(info.volume)
In this case the attributes define that the task at hand should run
PartitionVolume task — i.e. after volume has been
predecessors) — but before formatting each
It is also placed in the
Phases are ordered and group tasks together. All tasks in a phase are
run before proceeding with the tasks in the next phase. They are a way
of avoiding the need to list 50 different tasks as predecessors and
The final task list that will be executed is computed by enumerating all tasks in the package, placing them in the graph and sorting them topologically. Subsequently the list returned is filtered to contain only the tasks the provider and the plugins added to the taskset.
There are several abstractions in bootstrap-vz that make it possible
to generalize things like volume creation, partitioning, mounting and
package installation. As a rule these abstractions are located in the
base/ folder, where the manifest parsing and task ordering algorithm
are placed as well.