When making a request to create a dynamic host volumes, users can pass a node
pool and constraints instead of a specific node ID.
This changeset implements a node scheduling logic by instantiating a filter by
node pool and constraint checker borrowed from the scheduler package. Because
host volumes with the same name can't land on the same host, we don't need to
support `distinct_hosts`/`distinct_property`; this would be challenging anyways
without building out a much larger node iteration mechanism to keep track of
usage across multiple hosts.
Ref: https://github.com/hashicorp/nomad/pull/24479
* mkdir: HostVolumePluginMkdir: just creates a directory
* example-host-volume: HostVolumePluginExternal:
plugin script that does mkfs and mount loopback
Co-authored-by: Tim Gross <tgross@hashicorp.com>
Add several validation steps in the create/register RPCs for dynamic host
volumes. We first check that submitted volumes are self-consistent (ex. max
capacity is more than min capacity), then that any updates we've made are
valid. And we validate against state: preventing claimed volumes from being
updated and preventing placement requests for nodes that don't exist.
Ref: https://github.com/hashicorp/nomad/issues/15489
