C. What latency is acceptable for orders to reach the fulfillment system?

D. Can the fulfillment system participate in idempotent design to avoid duplicate orders?
C &D are correct as per explanation shared in trailing comment.

When designing an integration to send orders from Salesforce to a fulfillment system, an Integration Architect must carefully consider the constraints of both systems involved. Here are two critical system constraint questions to evaluate:
Can the fulfillment system participate in idempotent design to avoid duplicate orders?
Reasoning: Orders are a critical business transaction. If the integration fails mid-way (e.g., due to network issues or temporary system unavailability) and needs to retry sending the order, the fulfillment system must be able to handle receiving the same order multiple times without processing it more than once. Idempotency ensures that performing an operation multiple times has the same effect as performing it once.
Impact: If the fulfillment system is not designed to be idempotent, retries could lead to duplicate orders, incorrect inventory deductions, double billing, and significant operational errors. The integration design must account for this, either by ensuring the fulfillment system's capabilities or by implementing a mechanism in the integration layer (e.g., using a unique transaction ID and checking the status before resending).
What latency is acceptable for orders to reach the fulfillment system?
Reasoning: The acceptable delay or latency for an order to be transmitted from Salesforce to the fulfillment system directly impacts the choice of integration pattern.
Impact:
Real-time (low latency): If orders need to be fulfilled immediately (e.g., digital goods), a synchronous integration pattern like Request & Reply might be necessary, potentially using a middleware or Apex continuations to manage long-running responses if the fulfillment system is slow.
Near real-time / Asynchronous (moderate latency): If a short delay is acceptable (e.g., a few seconds to minutes), an asynchronous pattern like publishing Platform Events or using Outbound Messaging might be suitable. These patterns decouple Salesforce from the fulfillment system, impr...

C, D are correct

Constraint mean that base on the limitation about the resources & support of external system, we will decide the solution.
A&D are correct.

BC
B. Which system will validate order shipping addresses? is an important consideration because incorrect shipping addresses can cause delivery problems and potentially result in dissatisfied customers. Determining which system will be responsible for validating shipping addresses can help ensure that orders are processed correctly and delivered to the correct location.

C. What latency is acceptable for orders to reach the fulfillment system? is important because it determines the speed at which orders will be processed and shipped. If the fulfillment system is unable to meet the required latency, orders may be delayed, which can impact customer satisfaction and the overall efficiency of the order fulfillment process. By considering the acceptable latency upfront, the integration can be designed to meet the needs of both the sales and fulfillment systems.