DEA-C01 Practice Test 16 — 15 Questions

Question 1

A company runs a production Amazon RDS for MySQL database with Multi-AZ deployment. The database experiences high read latency during peak hours. The company wants to improve read performance with minimal application changes. Which solution should a data engineer recommend?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Create one or more read replicas in a different Availability Zone.. Creating read replicas in a different Availability Zone offloads read traffic from the primary DB instance, reducing read latency during peak hours. Read replicas in Amazon RDS for MySQL are asynchronous replicas that can serve SELECT queries, requiring minimal application changes (only a new connection endpoint). This directly addresses high read latency without altering the existing Multi-AZ setup.

Answer

Use Amazon DynamoDB Accelerator (DAX) as a caching layer.

Answer

Increase the DB instance size to a larger instance class.

Answer

Enable Multi-AZ on the existing instance.

Question 2

A company uses Amazon Redshift for its data warehouse. The data engineer notices that the most frequently accessed table is sorted by date, but queries often filter by customer_id. The table has 500 million rows and uses AUTO distribution style. What change would MOST improve query performance?

Accepted Answer

Change the sort key to include customer_id as a compound sort key.. Since queries frequently filter by customer_id but the table is sorted only by date, Redshift must scan all rows that match the date range and then filter by customer_id. By adding customer_id as a compound sort key (date, customer_id), Redshift can use zone maps to skip blocks that don't contain the requested customer_id within the date range, dramatically reducing the number of rows scanned and improving query performance.

Answer

Change distribution style to KEY on customer_id.

Answer

Change distribution style to EVEN.

Answer

Change the sort key to an interleaved sort key on date and customer_id.

Question 3

Which TWO methods can be used to enforce least-privilege access to an Amazon S3 bucket? (Choose two.)

Accepted Answer

Use IAM policies to grant specific permissions to users and roles.. IAM policies allow you to grant granular, specific permissions to individual users and roles, adhering to the principle of least privilege by explicitly allowing only the actions required. This avoids granting broad or default permissions, ensuring that each identity has only the access necessary for its function.

Answer

Set bucket ACLs to allow full control to the bucket owner only.

Answer

Configure a VPC endpoint to restrict access to the bucket.

Answer

Generate pre-signed URLs for all access.

Question 4

An organization needs to audit all access to their S3 buckets for compliance purposes. They want to log both successful and failed API calls. Which AWS service should be used?

Accepted Answer

AWS CloudTrail. AWS CloudTrail is the correct service because it records all API calls made to S3, including both successful and failed requests, and delivers log files to an S3 bucket for auditing and compliance. CloudTrail captures management events (e.g., CreateBucket) and, when enabled, data events (e.g., GetObject, PutObject) for S3, providing a complete audit trail of access.

Answer

Amazon CloudWatch Logs

Answer

AWS Config

Answer

VPC Flow Logs

Question 5

A company uses Amazon Redshift for data warehousing. The data engineer notices that query performance has degraded over time. The tables are frequently updated with new data, and the data engineer suspects that the distribution style is causing data skew. Which distribution style should the data engineer use to minimize data skew?

Accepted Answer

EVEN distribution. EVEN distribution (D) distributes rows across all slices in a round-robin fashion, ensuring each slice holds approximately the same number of rows. This eliminates data skew caused by uneven distribution keys, which is the suspected issue when query performance degrades over time with frequent updates. By avoiding any dependency on column values, EVEN distribution guarantees balanced data distribution regardless of data characteristics.

Answer

KEY distribution on a column with high cardinality

Answer

AUTO distribution

Answer

ALL distribution

Question 6

A company uses AWS Glue to process streaming data from Amazon Kinesis Data Streams. The job reads JSON records and writes Parquet to Amazon S3. Recently, the job started failing with 'Out of Memory' errors. Which change is MOST likely to resolve the issue?

Accepted Answer

Increase the number of DPUs allocated to the Glue job.. The 'Out of Memory' error in AWS Glue indicates that the job's allocated resources are insufficient for the data volume or processing complexity. Increasing the number of DPUs (Data Processing Units) directly increases the available memory and compute capacity, which is the most straightforward fix for OOM errors in Glue streaming jobs. Option C is correct because it addresses the root cause—resource exhaustion—by scaling the job horizontally.

Answer

Enable compression on the Kinesis stream.

Answer

Change the output format from Parquet to ORC.

Answer

Reduce the streaming batch size in the Glue job configuration.

Question 7

Refer to the exhibit. An IAM policy is attached to an EC2 instance role that runs a data ingestion application. The application reads files from an S3 bucket 'data-lake-primary' and sends records to a Kinesis stream named 'clickstream'. The application is failing with an 'AccessDenied' error when trying to read from S3. What is the MOST likely cause?

Accepted Answer

The policy does not include the s3:ListBucket permission.. The application reads files from an S3 bucket, which requires both s3:GetObject (to read the object) and s3:ListBucket (to list objects in the bucket, typically needed for operations like listing or navigating the bucket). Without s3:ListBucket, the SDK may fail with an AccessDenied error when it tries to enumerate objects or validate the bucket path, even if s3:GetObject is present. Option D correctly identifies this missing permission as the most likely cause.

Answer

The actions are specified incorrectly; they should be s3:GetObject and s3:PutObject only.

Answer

The policy is not attached to the EC2 instance role.

Answer

The Kinesis stream name is incorrect.

Question 8

A company uses Amazon DynamoDB to store session data for a web application. The application experiences throttling errors during peak traffic. The data engineer observes that the table's read capacity is consistently at 100% and the write capacity is at 20%. The engineer needs to resolve the throttling with minimal cost. Which solution should the engineer implement?

Accepted Answer

Implement DynamoDB Accelerator (DAX) to cache read-heavy workloads.. The issue is read-heavy throttling with read capacity at 100% while write capacity is low. Implementing DynamoDB Accelerator (DAX) provides an in-memory cache that offloads read traffic from the table, reducing read capacity consumption and eliminating throttling without increasing provisioned capacity. This is the most cost-effective solution as it avoids scaling costs and leverages caching for repeated reads.

Answer

Increase the provisioned read capacity units for the table.

Answer

Enable DynamoDB auto scaling for read capacity.

Answer

Decrease the provisioned write capacity units to free up budget for reads.

Question 9

A company is running a production Amazon RDS for MySQL Multi-AZ DB instance. The database experiences a sudden spike in read requests, causing performance degradation. The company needs to improve read scalability with minimal application changes. Which solution should the data engineer recommend?

Accepted Answer

Create an Amazon RDS Read Replica and update the application to use it for read queries.. Amazon RDS Read Replicas allow you to offload read traffic from the primary DB instance by creating asynchronous replicas that can serve read queries. This directly addresses the spike in read requests with minimal application changes—only the connection string for read queries needs to be updated. Multi-AZ is for high availability, not read scaling, and increasing instance size is a vertical scaling approach that doesn't leverage the horizontal read scalability of replicas.

Answer

Implement DynamoDB Accelerator (DAX) in front of the database.

Answer

Enable Multi-AZ on the existing DB instance.

Answer

Increase the DB instance size to a larger instance class.

Question 10

A company is using Amazon RDS for MySQL and wants to automate backups for point-in-time recovery. Which TWO actions should be taken? (Choose TWO.)

Accepted Answer

Enable automated backups with a retention period.. Enabling automated backups in Amazon RDS for MySQL allows point-in-time recovery (PITR) to any second within the retention period. Option C is correct because setting the backup retention period to the desired number of days (1–35 days) defines how far back you can perform PITR, and it must be explicitly configured to enable automated backups.

Answer

Use AWS Backup to schedule backups.

Answer

Enable Multi-AZ deployment.

Answer

Take manual snapshots daily.

Question 11

A data engineering team is designing a data lake on Amazon S3 for storing sensor data from IoT devices. The data is written in near real-time and needs to be queried using Amazon Athena. Which TWO configurations should the team implement to optimize query performance and minimize costs?

Accepted Answer

Store the data in Apache Parquet format.. Apache Parquet is a columnar storage format that allows Athena to read only the columns needed for a query, drastically reducing I/O and scan costs. Combined with compression (like Snappy or GZIP), Parquet minimizes the amount of data scanned per query, which directly lowers Athena's cost (charged per TB scanned) and improves query performance through predicate pushdown and efficient encoding.

Answer

Compress the data using GZIP.

Answer

Use S3 Standard-IA storage class.

Answer

Enable Requester Pays on the S3 bucket.

Question 12

A company uses an Amazon RDS for MySQL DB instance with Multi-AZ deployment. The primary DB instance fails unexpectedly. What happens to the database endpoint?

Accepted Answer

The existing endpoint continues to work and automatically points to the standby DB instance.. In a Multi-AZ RDS deployment, the DNS endpoint remains unchanged during a failover. When the primary DB instance fails, Amazon RDS automatically updates the DNS record to point to the standby instance in the other Availability Zone. This ensures the application can continue using the same endpoint without any manual intervention, providing high availability.

Answer

A new endpoint is created for the standby and the application must use the new endpoint.

Answer

The database becomes unavailable until the primary is restored from a snapshot.

Answer

The existing endpoint is deleted and a new endpoint is provided after manual DNS update.

Question 13

A company stores sensitive customer data in an Amazon S3 bucket. The security team requires that all data be encrypted at rest using a key that is automatically rotated every year. Which encryption solution should the data engineer use?

Accepted Answer

SSE-KMS with a customer managed key. SSE-KMS with a customer managed key is correct because it allows you to use an AWS KMS key that you control, enabling automatic annual key rotation via the KMS key rotation feature. This satisfies the security team's requirement for encryption at rest with a key that is automatically rotated every year, while maintaining control over the key lifecycle.

Answer

SSE-S3

Answer

SSE-C

Answer

Client-side encryption

Question 14

Refer to the exhibit. A data engineer is running an AWS Glue job that reads from an S3 bucket encrypted with a customer-managed KMS key. The job fails with the error shown. What is the most likely cause?

Accepted Answer

The IAM role used by the Glue job is missing the kms:Decrypt permission.. The error indicates that the AWS Glue job cannot access the S3 bucket because it lacks the necessary KMS permissions. Since the bucket is encrypted with a customer-managed KMS key, the IAM role assigned to the Glue job must include the kms:Decrypt permission to read the encrypted objects. Without this permission, the job fails when attempting to decrypt the data.

Answer

The S3 bucket policy denies the kms:Decrypt action.

Answer

The Glue job does not have permission to call kms:GenerateDataKey.

Answer

The KMS key policy does not grant the Glue service principal access.

Question 15

A company is using Amazon RDS for MySQL with Multi-AZ deployment. They notice that during a recent failover test, the application experienced a brief write outage. The application uses a connection string that points to the RDS instance endpoint. What is the MOST likely cause of the write outage?

Accepted Answer

The application is using the RDS instance endpoint instead of the cluster endpoint, so it does not automatically route to the standby after failover.. In a Multi-AZ RDS deployment, the instance endpoint always points to the current primary instance. During a failover, the DNS record for the instance endpoint is updated to point to the new primary, but existing connections to the old primary are dropped, and the DNS change can take time to propagate. The application's connection string using the instance endpoint means it does not automatically route to the standby during the failover transition, causing a brief write outage until the DNS update completes and the application reconnects. In contrast, using a cluster endpoint (available for Aurora, not standard RDS) or implementing retry logic in the application would mitigate this.

Answer

The application is using a read replica endpoint, which does not support write operations.

Answer

The application is connecting through a Network Load Balancer, which is not configured for cross-zone failover.

Answer

The application connection pool is exhausted because the failover caused all existing connections to drop simultaneously.