Coordinator:The coordinator is a long-lived server (e.g., an EC2 VM) that launches jobs and controls their execution. It contains all of the logic associated with a given computation in the form of per-worker finite-state-machine (FSM) descriptions. For each worker, the coordinator maintains an open TLS connection, the worker’s current state, and its state-transition logic. When the coordinator receives a message from a worker, it applies the state-transition logic to that message, producing a new state and sending the next RPC request to the worker using the AWS Lambda API calls.