In this case, we'll need a message broker to handle communication between our services, and an orchestrator that would coordinate the saga. Our order service would send a request to the orchestrator, which would then send commands to both the supply and payment services. Each of those would then do their part and send replies back to the orchestrator, through a reply channel available at the broker.
In this scenario, the orchestrator has all the logic needed to, well, orchestrate the transaction, and the services themselves don't need to be aware of any other services taking part in the saga.
If the orchestrator is sent a message that one of the services failed, for example, if the credit card has expired, it would then need to start the rollback. In our case, it would again use the broker to send an appropriate rollback command to specific services.
Okay, that's enough about eventual consistency for now. Let's now switch to other topics related...
