DVA-C02 Deployment 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.

• ✗

  Use the Ref function in the ECS service to reference the load balancer.

  Why it's wrong here

  Using the Ref function in the ECS service to reference the load balancer primarily retrieves the logical ID or a default attribute (like ARN for some resources) of the load balancer. While CloudFormation often infers implicit dependencies from Ref to ensure the referenced resource exists before its value is needed, it does not explicitly guarantee that the referenced resource is fully provisioned and operational before the dependent resource begins its creation. For critical operational readiness, DependsOn is more explicit and reliable.

• ✓

  Use the DependsOn attribute in the ECS service resource to reference the load balancer.

  Why this is correct

  The DependsOn attribute explicitly defines a creation, update, and deletion dependency between resources. By adding DependsOn: MyLoadBalancer to the ECS service resource, CloudFormation is instructed to ensure that MyLoadBalancer is completely provisioned and stable before it attempts to create or update the ECS service. This guarantees the load balancer is ready to accept registrations from ECS tasks, preventing deployment failures due to timing issues.

• ✗

  Define the load balancer before the ECS service in the template.

  Why it's wrong here

  The order in which resources are declared within a CloudFormation template's Resources section is purely for human readability and template organization. CloudFormation's engine determines the actual resource creation order based on an internal dependency graph, which is primarily built from explicit DependsOn attributes and implicit dependencies inferred from intrinsic functions like Ref or Fn::GetAtt. Without explicit instructions, the engine may attempt concurrent creation or an arbitrary order, leading to potential race conditions.

• ✗

  Use the Fn::GetAtt function to reference the load balancer.

  Why it's wrong here

  The Fn::GetAtt function is used to retrieve a specific attribute value from a resource, such as the DNSName or CanonicalHostedZoneName of a load balancer. While using Fn::GetAtt creates a data dependency, ensuring the attribute value is available when needed, it does not explicitly enforce the creation order or guarantee that the referenced resource is fully operational before the dependent resource starts. For strict operational sequencing, DependsOn is the appropriate mechanism.

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