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Shipping / Process Manager / Watchdog example

NOTE: In general, this is not intended to be the first example you touch when exploring Equinox (see https://github.com/jet/equinox#quickstart for a more progressive sequence of things to explore)

This project was generated using:

dotnet new -i Equinox.Templates # just once, to install/update in the local templates store
dotnet new eqxShipping

The purpose of this template is to demonstrate the implementation of a Process Manager using Equinox that manages the enlistment of a set of Shipment Aggregate Root items into a separated Container Aggregate Root as an atomic operation.

Implementation notes:

  • processing is fully idempotent; retries, concurrent or overlapping transactions are intended to be handled thoroughly and correctly
  • if any Shipments cannot be Reserved, those that have been get Revoked, and the failure is reported to the caller
  • includes a Watchdog console app (based on dotnet new proReactor --blank) responsible for Pumping any abandoned / stuck transactions neglected by e.g. processing within a HTTP request that times out and is not retried by the client through to their conclusion.

Exercise / hole

A remaining hole is that multiple concurrent Finalization transactions are not prevented (which I believe is different from the actual app semantics at the present time - Finalization is intended to be a final act 😸). It may be a interesting exercise for the reader to add processing to the FinalizationTransaction (and Container) such that one or more of the following behaviors apply:

  • Gate the processing via a reservation on the container (you'll definitely need a Watchdog!)
  • Do an optimistic pre-flight check, visiting the Container to see if it's already Finalized
  • If one reaches the Finalize action but determine it has already been completed by a competing writer, switch to a reverting mode (but that would open the possibility of multiple Assigned events)
  • Register the Finalization intent on the Container once the Reservations have been attained, then mark it Finalized after that

Usage instructions

See Watchdog/README.md for some minimal setup instructions.