DOP-C02 Resilient Cloud Solutions 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.

• ✗

  Store session state in an EBS volume attached to each instance

  Why it's wrong here

  EBS volumes are zone-bound and can only be attached to a single EC2 instance at a time, so storing session state there tightly couples session data to a specific host. If that instance or its Availability Zone fails, the session data becomes inaccessible until manual recovery steps such as detaching and reattaching the volume are taken, causing downtime. Highly available architectures must store session state in a shared external service like ElastiCache or DynamoDB that survives individual instance failures.

• ✓

  Deploy EC2 instances in multiple Availability Zones

  Why this is correct

  Distributing EC2 instances across multiple Availability Zones ensures the application can tolerate a complete failure of one physical data center, because the remaining instances continue to serve traffic. Each AZ has independent power, cooling, and network connectivity, so an outage in one AZ does not affect the others. This redundancy is the fundamental building block of high availability on AWS and is a necessary condition for achieving a higher service-level agreement.

• ✗

  Use a single NAT instance in a public subnet

  Why it's wrong here

  A single NAT instance in a public subnet is a monolithic point of failure in the network path for all private subnet traffic. If the instance fails, is terminated, or becomes unhealthy due to OS-level issues, all outbound internet access from the private subnets is lost. Moreover, a NAT instance is a self-managed EC2 instance that requires manual failover, unlike a NAT gateway, which is fully managed and can be deployed per Availability Zone to provide redundant connectivity.

• ✗

  Use only M5 instance types for better performance

  Why it's wrong here

  Instance type selection, such as choosing M5 general-purpose instances, influences compute, memory, and network performance but has no bearing on the resilience or availability of the architecture. Availability depends on redundancy through multiple instances, health checking, auto scaling, and distribution across Availability Zones. A larger or different instance type does not protect against failures; it can even increase the blast radius if a single instance hosts critical state without replication.

• ✓

  Use an Application Load Balancer to distribute traffic

  Why this is correct

  An Application Load Balancer provides Layer-7 traffic distribution and performs active health checks on registered targets, automatically removing unhealthy instances from the rotation and rerouting traffic to healthy ones. When combined with instances spread across multiple Availability Zones, the ALB becomes a regional, fault-tolerant entry point that absorbs failures and balances load dynamically. This makes it a core component of a highly available architecture, although it must be paired with redundant targets to be effective.

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