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Home Forums AWS AWS Certified Solutions Architect Associate DB instance failover

  • DB instance failover

  • theodosiostziomakas

    Member
    January 17, 2025 at 4:38 pm

    <div>A top investment bank is in the process of building a new Forex trading platform. To ensure high availability and scalability, you designed the trading platform to use an Elastic Load Balancer in front of an Auto Scaling group of On-Demand EC2 instances across multiple Availability Zones. For its database tier, you chose to use a single Amazon Aurora instance to take advantage of its distributed, fault-tolerant, and self-healing storage system.

    In the event of system failure on the primary database instance, what happens to Amazon Aurora during the failover? </div>

    A) Amazon Aurora flips the canonical name record (CNAME) for your DB Instance to point at the healthy replica, which in turn is promoted to become the new primary.

    B) Aurora will attempt to create a new DB Instance in the same Availability Zone as the original instance and is done on a best-effort basis.

    C) Amazon Aurora flips the A record of your DB Instance to point at the healthy replica, which in turn is promoted to become the new primary.

    D) Aurora will first attempt to create a new DB Instance in a different Availability Zone of the original instance. If unable to do so, Aurora will attempt to create a new DB Instance in the original Availability Zone in which the instance was first launched.

    I answered A, but it’s wrong. Why?

    Thanks,

    Theodosios.

  • Nikee-TutorialsDojo

    Administrator
    January 18, 2025 at 8:31 am

    Hello theodosiostziomakas,

    Thank you for posting here. Let me explain why Option 2 is the correct answer to the question.

    In the given scenario, a single Amazon Aurora instance is used, and there is no mention of Aurora Replicas being configured. When a single-instance Aurora database experiences a system failure, Amazon Aurora attempts to create a new DB instance in the same Availability Zone as the original instance. This process is conducted on a best-effort basis, meaning it depends on the availability of resources in that AZ. If the Availability Zone is experiencing broader issues, this effort may not succeed.

    Option 1 describes the failover process when Amazon Aurora Replicas are present. In such a case, Aurora promotes an existing healthy replica and flips the CNAME record to point to the new primary instance. However, since the scenario explicitly uses a single Aurora instance (with no replicas mentioned), this failover mechanism does not apply. Without replicas, Aurora must attempt to replace the failed instance, aligning with the behavior described in Option 2.

    In summary, the correct answer is Option 2 because the described failover mechanism aligns with the behavior of a single-instance Aurora setup. Option 1 applies only when replicas are available, which is not the case in the scenario.

    Thank you for bringing this important distinction to our attention, and hope this clears up any confusion you have.

    Best regards,
    Nikee @ Tutorials Dojo

  • theodosiostziomakas

    Member
    January 18, 2025 at 7:22 pm

    I understood it, now. Thank you very much for clearing up my confusion.

    Thanks

    Theodosios

    • Nikee-TutorialsDojo

      Administrator
      January 20, 2025 at 9:29 am

      Always happy to help. Good luck with your exam!

      Regards,

      Nikee @ Tutorials Dojo

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