Composable Orchestration

Overview: Layer 2 — choreograph functions as YAML flows with Event Script.

At a glance

  • What — Event Script, a YAML DSL that describes an end-to-end transaction as a flow that choreographs functions — orchestration as configuration, not code.
  • Why it matters — changing how a transaction runs means editing a flow, not rewriting Java; roughly half config, half code.
  • Where it sits — Layer 2 of the ascent, built on the event-driven foundation.
  • For developers and architects orchestrating composable functions.

Event Script is a Domain Specific Language (DSL) that uses YAML to represent an end-to-end transaction flow. A transaction is a business use case, and the flow can be an API service, a batch job or a real-time transaction.

It moves orchestration out of code and into configuration: instead of writing Java that calls one function after another, you describe the sequence as a flow in YAML. Roughly half the work becomes configuration, half stays code (the functions themselves). A flow builds on the event-driven foundation beneath it — it never references a function's class, only its route name.

The mental model

  • A flow is an ordered set of tasks with one entry point (first.task) and one or more terminal tasks.
  • Each task runs a function (named by route) — a task is a function in its flow-step role. Input and output data mapping move values between the flow and the function's scope.
  • A task's execution type decides what happens next: sequential, decision, parallel, fork, pipeline, response, end, or sink.
  • A per-transaction state machine (model) holds intermediate results across the stateless functions.
  • A flow adapter (HTTP via rest.yaml, or Kafka) drives a flow from outside and returns its result.

See also