I think the answer is probably like most things: it depends.
- If the external service supports idempotent operations, use that option.
- If the external service doesn't, but has a "retrieval" feature (i.e. lookup if the thing already exists, e.g fetch refunds on a given payment), use that first.
- If the system has neither, assess how critical it is to avoid duplicates.
- If the external service supports idempotent operations, use that option.
- If the external service doesn't, but has a "retrieval" feature (i.e. lookup if the thing already exists, e.g fetch refunds on a given payment), use that first.
- If the system has neither, assess how critical it is to avoid duplicates.