Note: This is a live blog, I've not spent time editing, formatting, etc
TaskFlow answers the “Statemanagement” issue.
- Workflows w/o state makes recovery an issue.
- Also reliablility can be an issue.
- Race conditions
- Manager <-> API Boundary
- undefined states
Why does state matter?
- Reliability, consistency
- Upgrades, or recovering from the upgrades
- Easy to understand workflows
TaskFlow is not:
- A webservice, no API (see: minstral)
- Doesn't fix everything, no rainbow ponies yet.
- Still needs careful coding
The discrete component of TaskFlow is a “task” those are built into flows. The engine translates the flow into simpler things, a compiler of sorts. Following that, are a number of state transitions a flow will progress through at execution time. This provides a deep level for state analysis.
- Executes and reverts one action
- Recieves inputs, declares outputs
- Composes tasks into useful structures (also subflows)
- Imposes definition of order onto the tasks and subflows
- linear, unordered, or toopological
- Runs your flow, reliable resumable manner
- well defined transitions
- allows deployers/developers of a service to select an engine to fit the setup
- backed by different setups
- — Single / Multi-threaded
- — Distributed (WIP)
TaskFlow != Minstrel, however, that is subject to change #openstack
“Is TaskFlow similar to the Amazon workflow service?” – It can be used in that way, but that's not what its targeted at #openstack
“You allow for parallel action, do you allow for synchronization” – We'll see how the greater #openstack goes and TaskFlow will follow
“At what point do you write state” – At each transition, and when a task returns info #openstack
@rackninja: Taskflow is a general workflow library. The hope is that it will consumed by #openstack services as the standard eventually
- Task state / progress, can be a DB, or filesystem, or in memory
- Allows reconstruction of flows and tasks
- Can view the step by step actions of a workflow… could be useful for audits and troubleshooting
- Initial and deriviave tasks required to fulfill an action
- Can be moved to another worker for execution or so
- Jobs automatically posted, completed, claimed, etc.
- Backed by MQ, Zookeeper, etc
- Release 0.1
- Tagged and pypi
- Foundational concepts, tasks, flows, persistance, etc
- Distributed engine
- lock service
- job/job board