State machines

Blazar objects (leases, reservations, and events) each have a status. This document describes statuses in detail.

Lease status

Lease statuses are categorized into two types: stable or transitional. In the state machine shown below, stable statuses are drawn as black nodes while transitional statuses are drawn as gray nodes. Status transitions are triggered by an API call or an event in a lease.

A lease has the following four stable statuses:

  • PENDING: A lease has been successfully created and is ready to start. The lease stays in this status until it starts.

  • ACTIVE: A lease has been started and is active.

  • TERMINATED: A lease has been successfully terminated.

  • ERROR: Unrecoverable failures happened to the lease.

Transitional statuses are as follows:

  • CREATING: A lease is being created.

  • STARTING: A lease is being started.

  • UPDATING: A lease is being updated.

  • TERMINATING: A lease is being terminated.

  • DELETING: A lease is being deleted. Any status can change to this status because delete is the highest prioritized operation. e.g. when a lease hangs up in the STARTING status, delete should be allowed.

If some action can cause an invalid status transition, the action is denied. E.g. If a user sends an Update Lease request while it is starting, the Update Lease request is denied because the transition from STARTING to UPDATING is invalid.


Reservation status

A reservation has the following four statuses. Lowercase letters are used for backward compatibility:

  • pending: A reservation has been successfully created and is ready to start. The reservation stays in this status until it starts.

  • active: A reservation has been started and is active.

  • deleted: Reserved resources have been successfully released.

  • error: Unrecoverable failures happened to resources.


Event status

Event statuses are as follows.


Relationships between statuses

The following table shows conditions of statuses of reservations and events that have to be satisfied for each lease status.






start_lease: UNDONE , end_lease: UNDONE



start_lease: UNDONE , end_lease: UNDONE


pending or active or error

start_lease: IN_PROGRESS , end_lease: UNDONE



start_lease: DONE , end_lease: UNDONE


active or deleted or error

start_lease: DONE , end_lease: IN_PROGRESS



start_lease: DONE , end_lease: DONE


Any status

Any status


Any status

Any status other than IN_PROGRESS

blazar/status module

The blazar/status module defines and manages these statuses.