The cluster maintains a distributed map of jobs (job-id -> job-state). Job state should be a clojure map that contains only serializable values.
By contract, the cluster will maintain a single core.async go-loop that handles calling the job multi-method 'run' on startup and timeout events and message arrival events. When the cluster migrates data to/from a node due to a node outage or controlled lifecycle (e.g. rolling upgrade), the async loop and topic handler is migrated to a successor node.
NOTE: Due to the use of topics, messages to jobs that arrive during cluster migration will be lost.
Each cluster member is assigned a subset of values in the map by the HazelCast partitioner. When values are added to the map, they are 'scheduled' which includes being setup to listen to job topic events and are immediately passed to a core.async go process, the "run loop". When they are removed from the map, they are unscheduled and their associated state and run loop is cleaned up.
The run loop will call the scheduler/run method with an initial state and registered a control handler for updating the scheduler run loop.
Jobs that receive events via the job topic bus have a message handler after which a :resume input is sent to the control loop.
- Scheduler
- Contains local entry listener ID and the set of local Controllers
- Distributed Job Map (each member owns subset of entries according to partitioning strategy)
- Run Loop - a core.async go-loop that executes the workflow
- Listener - a topic listener for this job to receive messages
- Controller ('ctrl') - a control channel that is used to manage the run loop
- LocalEntryListener
- Called when member when owned key-value pairs are added/removed
- Registers a listener to the job's topic
- Starts the local core.async loop
- MigrationListener
- Called when partitions are being migrated
- Used to shut down Run Loop and Listener (if source is still up)
- Creates new Run Loop and Listener on new cluster