A SaaS platform plans to run in two AWS Regions for lower latency. The team wants to enable active-active writes (both regions accept updates) to avoid failover downtime. However, the business requires strong consistency for order status transitions (for example, only one transition from “Paid” to “Shipped” must be allowed).
Which statement is the best architectural choice to meet the consistency requirement?
Answer choices
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
Use active-active writes only when the workload tolerates eventual consistency; for strongly consistent transitions, use a single-writer pattern with failover (active-passive/pilot light).
Strong consistency requirements typically conflict with multi-master active-active replication semantics, so single-writer designs are safer.
Active-active writes always provide strong consistency because AWS replicates data across Regions automatically and immediately.
Multi-Region replication is not always strongly consistent for conflicting updates, especially for multi-master patterns.
Active-active writes can be used safely by simply enabling retries and expecting the application to resolve conflicts without coordination.
Retrying does not guarantee correct single-transition semantics; conflict resolution still requires a consistent authority.
To ensure strong consistency, run both Regions with different IAM roles and block cross-Region writes at the API layer only.
IAM controls do not change replication consistency guarantees; the data model and write authority still need to be single-writer.
Common exam trap
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Technical deep dive
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
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Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
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FAQ
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The correct answer is: Use active-active writes only when the workload tolerates eventual consistency; for strongly consistent transitions, use a single-writer pattern with failover (active-passive/pilot light). — Active-active designs commonly involve multi-master replication and can result in eventual consistency or conflict windows, which is risky for workflows that must enforce strong ordering and unique transitions across Regions. Since the order status transition requirement is strict (only one valid transition), the safer approach is a single-writer pattern where exactly one Region is authoritative for writes, and the other Region takes over via failover. Active-passive or pilot light designs maintain resiliency while keeping strong consistency guarantees at the application/data layer. Why others are wrong: The claim that active-active always provides strong consistency is incorrect; cross-Region replication can’t universally guarantee immediate, globally ordered updates. Retries alone can’t enforce a single transition if both Regions can issue writes; coordination or a single authority is required. Restricting writes with IAM or API checks does not solve the underlying replication and authorization model necessary for strongly consistent, conflict-free state transitions.
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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