SOA-C02 Reliability and Business Continuity Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  Deploy EC2 instances in a single Availability Zone behind an Application Load Balancer. Enable Multi-AZ for the RDS MySQL DB instance.

  Why it's wrong here

  Although enabling Multi-AZ for RDS protects the database tier from an Availability Zone failure, placing all EC2 instances in a single Availability Zone leaves the application tier as a single point of failure. An Application Load Balancer is a regional service, but if all registered targets reside in one AZ and that AZ becomes unavailable, there are no healthy targets left to receive traffic. The web application therefore becomes unreachable even though the database remains accessible, so this configuration does not meet high-availability requirements.

• ✗

  Deploy EC2 instances in two Availability Zones and place them behind a Network Load Balancer. Keep RDS MySQL as a single-AZ deployment.

  Why it's wrong here

  A Network Load Balancer operates at Layer 4 and lacks HTTP-aware features such as host-based or path-based routing, but the more critical issue is that a single-AZ RDS MySQL instance is a single point of failure. If that AZ fails, the database will not automatically fail over to another AZ because Multi-AZ is not enabled. Even with EC2 instances spread across two AZs, the application cannot function without its database, and the NLB does nothing to mitigate database downtime.

• ✗

  Deploy EC2 instances in two Availability Zones. Configure an RDS MySQL Read Replica in a second Availability Zone and route read traffic to it.

  Why it's wrong here

  RDS MySQL Read Replicas are designed for read traffic scaling and do not provide automatic failover for the primary instance. In the event of an AZ failure affecting the primary, the read replica does not automatically become the new primary—promotion requires manual intervention and may cause data loss if the replica has not caught up. Routing read traffic to the replica does not preserve write availability, and the primary DB remains a single point of failure for the application.

• ✓

  Deploy EC2 instances in two Availability Zones and place them behind an Application Load Balancer. Enable Multi-AZ for the RDS MySQL DB instance.

  Why this is correct

  This architecture provides high availability for both the application and database layers. The EC2 fleet spans two Availability Zones behind an Application Load Balancer, which performs health checks and distributes request traffic to healthy targets, so an instance or AZ failure is absorbed by the remaining targets. Enabling Multi-AZ on RDS MySQL automatically provisions a synchronous standby in a second AZ and performs automatic failover to that standby if the primary fails, thereby eliminating single points of failure across the stack.

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