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Difficulty: MediumDatabase High Availability

A company hosts a production application on an Amazon Aurora MySQL DB cluster. The cluster contains one primary (writer) instance and three replica (reader) instances named reader-1, reader-2, and reader-3, distributed across three Availability Zones. To support business continuity, a SysOps Administrator must ensure that if the primary instance fails, reader-2 is promoted to the primary writer role first. If reader-2 is unavailable, reader-1 must be promoted next. Which configuration will meet these requirements?

  1. Set the Promotion Tier of reader-2 to Tier 00, reader-1 to Tier 11, and reader-3 to Tier 22.Answer
  2. B
    Set the Promotion Tier of reader-2 to Tier 1515, reader-1 to Tier 1414, and reader-3 to Tier 1313.
  3. C
    Configure an Amazon Route 53 failover routing policy pointing to the individual endpoints of reader-2 as primary and reader-1 as secondary.
  4. D
    Modify the DB cluster parameter group to define the failover sequence favoring reader-2, followed by reader-1.

Answer

Set the Promotion Tier of reader-2 to Tier 00, reader-1 to Tier 11, and reader-3 to Tier 22.
The correct configuration is to set the Promotion Tier of reader-2 to Tier 00, reader-1 to Tier 11, and reader-3 to Tier 22. Amazon Aurora determines which replica to promote to the primary writer role based on the Promotion Tier configuration of each DB instance. Aurora evaluates these tiers in ascending order, where Tier 00 has the highest priority and Tier 1515 has the lowest priority. Therefore, setting reader-2 to Tier 00 ensures it is evaluated first, setting reader-1 to Tier 11 ensures it is evaluated second, and setting reader-3 to Tier 22 ensures it is evaluated last.

Step-by-Step Solution

1
Determine the mechanism Aurora uses to prioritize replica promotion during a failover event.
Identify that Amazon Aurora uses Promotion Tiers (from 00 through 1515) defined at the DB instance level to manage failover priority.
This establishes that we must configure instance-level promotion settings rather than cluster parameter groups or DNS routing.
2
Analyze the priority order of the Promotion Tier values.
Verify that Tier 00 represents the highest priority (first to be promoted) and Tier 1515 represents the lowest priority.
This allows us to correctly assign the tiers to ensure reader-2 is prioritized over reader-1, which in turn is prioritized over reader-3.
3
Assign the appropriate Promotion Tiers to each replica instance.
Assign Tier 00 to reader-2, Tier 11 to reader-1, and Tier 22 (or higher, up to Tier 1515) to reader-3.
This guarantees that if the primary instance fails, Aurora will evaluate reader-2 first, then reader-1, and finally reader-3.

Key Concept

Amazon Aurora Failover Priority and Promotion Tiers
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Topics

Database High Availability

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