DBS-C01 Deployment and Migration Practice Question
A company is deploying a new application on Amazon RDS for PostgreSQL. The application requires a database with a specific parameter group that sets 'max_connections' to 500 and 'shared_buffers' to 25% of the instance memory. The company uses CloudFormation to deploy the RDS instance. The CloudFormation template creates a DBInstance with a DBParameterGroup. The deployment fails because the parameter group cannot be associated with the DB instance. What is the most likely cause?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The parameter group uses an invalid value for 'shared_buffers' because it must be an integer, not a percentage.
In Amazon RDS for PostgreSQL, the 'shared_buffers' parameter must be specified as an integer value (in 8 KB blocks) or a string ending with 'kB', 'MB', or 'GB', not as a percentage of instance memory. Using a percentage like '25%' is invalid and causes the parameter group association to fail. Option B is incorrect because 'max_connections' can be set to 500 as long as it does not exceed the instance class limits, but that is not the issue here. Option C is incorrect because CloudFormation automatically handles dependencies when resources are referenced; explicit DependsOn is not required. Option D is incorrect because CloudFormation templates can reference resources across regions only if explicitly designed, but the region mismatch would cause a different error, not parameter group association failure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The parameter group uses an invalid value for 'shared_buffers' because it must be an integer, not a percentage.
Why this is correct
RDS requires absolute values for 'shared_buffers', not percentages.
- ✗
The 'max_connections' value of 500 exceeds the allowed maximum for the instance class.
Why it's wrong here
Max_connections can be set to 500; it depends on instance memory.
- ✗
The CloudFormation template does not include a DependsOn clause linking the DBParameterGroup to the DBInstance.
Why it's wrong here
CloudFormation automatically handles dependencies when resources reference each other.
- ✗
The DBParameterGroup is not in the same region as the DBInstance.
Why it's wrong here
CloudFormation deploys resources in the same region by default.
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