DVA-C02 Ref function 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 parameter reference 'Ref: StageName' in the environment variable mapping.

  Why this is correct

  This is the correct approach for dynamically injecting a value provided at deployment time into a Lambda function's environment variables. `Ref` is a CloudFormation intrinsic function that retrieves the value of a top-level parameter declared in the `Parameters` section of the template. By defining `StageName` as a parameter and referencing it with `Ref: StageName` in the Lambda's environment variable configuration, the developer ensures the stage name (e.g., 'dev', 'prod') is passed during stack creation or update, making the application adaptable across different environments without code changes.

• ✗

  Define the environment variable as 'Stage: dev' in the Lambda function configuration.

  Why it's wrong here

  Hardcoding the environment variable `Stage` to a static value like 'dev' directly within the Lambda function configuration prevents the application from being easily deployed to multiple environments (e.g., 'test', 'prod') without modifying the CloudFormation template itself. This approach lacks flexibility and violates the principle of separating configuration from code, making it cumbersome to manage different deployment stages. It would require manual updates for each environment, increasing the risk of errors and reducing automation capabilities.

• ✗

  Use 'Fn::GetAtt: [AWS::StackName, Outputs.StageName]' to get the stage name.

  Why it's wrong here

  The `Fn::GetAtt` intrinsic function is used to retrieve an attribute from a resource in the *current* stack, not to reference a parameter or an output from *another* stack. While `AWS::StackName` is a pseudo-parameter, `Outputs.StageName` would imply an output from a resource *within* the `AWS::StackName` resource, which is incorrect syntax and usage. `Fn::GetAtt` is typically used with `[LogicalResourceId, AttributeName]`, and `StageName` is intended as a template parameter, not an attribute of `AWS::StackName` or an output of a resource in this context.

• ✗

  Use 'Fn::ImportValue: StageName' to import from another stack.

  Why it's wrong here

  `Fn::ImportValue` is specifically designed for sharing output values between *different* CloudFormation stacks within the same AWS account and region. It allows a stack to consume a value that was explicitly exported by another stack using `Fn::Export`. In this scenario, the question implies `StageName` is a parameter for the *current* stack being deployed, not an output from a separate, pre-existing stack that needs to be imported. Therefore, using `Fn::ImportValue` is inappropriate for referencing a parameter defined within the same template.

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