Hyper.Img.Db.Lease (Hyper v0.1.0)

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A single running VM's claim on an image (and transitively, every blob in that image's chain).

  • take a lease -> insert a row (your "increment, before starting the VM")
  • release -> delete the row (your "decrement, when done")
  • heartbeat -> bump expires_at (keeps a live VM's claim fresh)

Because the claim is owned and expiring, a node that dies mid-VM does not leak a reference - its lease simply lapses, and the blob becomes deletable again without anyone running the missing decrement.

Summary

Functions

bump(image_id, vm_id, ttl)

Take a lease on the given image, bumping its expiry if one already exists.

changeset(lease, attrs)
default_ttl()
reap_expired()

Reap the expired leases. This is mostly implemented to clean up the database, but does nothing outside of that. Returns the number of leases removed.

release(vm_id)

Release the lease issued to the given node_id and the given vm_id. Since each VM only ever uses one image, it is not necessary to specify the image id.

Functions

bump(image_id, vm_id, ttl)

@spec bump(Hyper.Img.id(), Hyper.Vm.Id.t(), Unit.Time.t()) ::
  {:ok,
   %Hyper.Img.Db.Lease{
     __meta__: term(),
     expires_at: term(),
     id: term(),
     image: term(),
     image_id: term(),
     inserted_at: term(),
     node_id: term(),
     vm_id: term()
   }}
  | {:error, Ecto.Changeset.t()}

Take a lease on the given image, bumping its expiry if one already exists.

Upserts on (node_id, vm_id) - the same call both takes a fresh lease and heartbeats a live one.

changeset(lease, attrs)

default_ttl()

reap_expired()

Reap the expired leases. This is mostly implemented to clean up the database, but does nothing outside of that. Returns the number of leases removed.

release(vm_id)

@spec release(Hyper.Vm.Id.t()) :: :ok

Release the lease issued to the given node_id and the given vm_id. Since each VM only ever uses one image, it is not necessary to specify the image id.