DEA-C01 Practice Test 14 — 15 Questions

Question 1

A company is running a production Amazon Aurora PostgreSQL database. The database experiences high write latency during peak hours. The data engineer suspects that the issue is due to a large number of small transactions. Which action would MOST effectively reduce write latency?

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

Accepted Answer

Increase the instance size and use Provisioned IOPS storage. Increasing the instance size and using Provisioned IOPS storage directly addresses high write latency by providing more CPU and memory resources to handle transaction processing, while Provisioned IOPS ensures consistent, low-latency I/O for write operations. This is the most effective action because small transactions create high I/O demand, and scaling up the instance with dedicated IOPS reduces contention and write queue depth.

Answer

Enable parallel query for the database

Answer

Enable Aurora Auto Scaling for read replicas

Answer

Enable Performance Insights to identify the bottleneck

Question 2

A data engineer is designing a disaster recovery strategy for an Amazon RDS for PostgreSQL database. The primary database is in us-east-1. Which TWO approaches provide cross-region disaster recovery?

Accepted Answer

Configure cross-region automated backups to copy to us-west-2.. Amazon RDS supports cross-region automated backups, which automatically copy backup data (snapshots and transaction logs) from the primary region (us-east-1) to a secondary region (us-west-2). This provides a fully managed, automated disaster recovery solution that allows point-in-time recovery in the secondary region without manual intervention.

Answer

Take a manual snapshot and copy it to us-west-2 daily.

Answer

Use Amazon S3 cross-region replication for the database export.

Answer

Enable Multi-AZ in us-east-1.

Question 3

A company runs a data processing pipeline on Amazon EMR. The pipeline reads data from S3, processes it with Spark, and writes results back to S3. The engineer notices that the cluster is underutilized and wants to reduce costs. Which TWO actions should the engineer take? (Choose TWO.)

Accepted Answer

Use Spot instances for task nodes.. Using Spot instances for task nodes in Amazon EMR can significantly reduce costs, as Spot instances are spare EC2 capacity offered at up to 90% discount compared to On-Demand instances. Since task nodes are stateless and can be added or removed without affecting cluster stability, they are ideal candidates for Spot instances, allowing the engineer to lower expenses while maintaining processing capacity.

Answer

Change the master node to a larger instance type.

Answer

Enable EMRFS consistent view.

Answer

Increase the number of core nodes to improve parallelism.

Question 4

Refer to the exhibit. A data engineer attaches this bucket policy to an S3 bucket. A developer tries to upload an object to the bucket using the AWS CLI with the command: `aws s3 cp file.txt s3://my-bucket/`. The upload fails. What is the most likely reason?

Accepted Answer

The CLI command does not specify the encryption header, so the request is denied by the policy. The correct answer. The bucket policy condition `aws:SecureTransport` or similar encryption requirement (e.g., `s3:x-amz-server-side-encryption`) denies requests that do not include the required encryption header. The `aws s3 cp` CLI command does not automatically include the `x-amz-server-side-encryption` header; it uses SSE-S3 by default without setting the header explicitly. Therefore, the request is denied because the header is missing. Option B is incorrect because the policy does not depend on region. Option C is incorrect because the policy does not require a specific KMS key ID; it only requires the encryption header. Option D is incorrect because the IAM user likely has `s3:PutObject` permission, but the bucket policy explicitly denies the request due to missing encryption header.

Answer

The developer used the wrong AWS region

Answer

The CLI command does not include the required KMS key ID

Answer

The IAM user does not have s3:PutObject permission

Question 5

A company uses Amazon S3 to store sensitive customer data. The security team requires that all objects uploaded to a specific bucket be encrypted at rest using AWS KMS with a customer managed key. Which bucket policy statement should be applied to enforce this requirement?

Accepted Answer

Deny s3:PutObject unless s3:x-amz-server-side-encryption-aws-kms-key-id equals the specific KMS key ARN. The security team requires encryption at rest using AWS KMS with a customer managed key. The bucket policy must deny any s3:PutObject request that does not include the s3:x-amz-server-side-encryption-aws-kms-key-id condition key set to the specific KMS key ARN. This ensures that only objects encrypted with the designated customer managed key are allowed, enforcing the encryption requirement at the bucket policy level.

Answer

Deny s3:PutObject unless s3:x-amz-server-side-encryption is present

Answer

Allow s3:PutObject only if s3:x-amz-server-side-encryption is present

Answer

Deny s3:PutObject unless s3:x-amz-server-side-encryption equals AES256

Question 6

A data engineering team is using Amazon DynamoDB to store time-series data for a monitoring application. The table has a primary key of device_id (partition key) and timestamp (sort key). The application queries data for a specific device over a time range. The team notices that read latency is high for devices that generate large amounts of data. They need to improve query performance. Which solution should they implement?

Accepted Answer

Create a global secondary index with device_id as partition key and a truncated timestamp as sort key to distribute writes.. Creating a global secondary index (GSI) with device_id as the partition key and a truncated timestamp as the sort key helps distribute write traffic more evenly across partitions. This reduces hot partitions caused by devices that generate large amounts of data, thereby improving read latency by preventing throttling and reducing contention on a single partition.

Answer

Enable DynamoDB Accelerator (DAX) for the table.

Answer

Change the application to use eventually consistent reads.

Answer

Increase the read capacity units for the table.

Question 7

A company is migrating its on-premises Oracle database to Amazon Aurora PostgreSQL. The migration must have minimal downtime. The source database is 2 TB and runs on a single server. Which AWS service should be used for the migration?

Accepted Answer

AWS Database Migration Service (DMS). AWS Database Migration Service (DMS) is the correct choice because it supports homogeneous migrations from Oracle to Amazon Aurora PostgreSQL with minimal downtime using ongoing replication (change data capture). DMS can handle a 2 TB source database by performing a full load followed by continuous replication of changes from the Oracle redo logs, allowing the target Aurora database to stay nearly in sync until cutover.

Answer

AWS DataSync

Answer

Amazon S3 Transfer Acceleration

Answer

AWS Snowball Edge

Question 8

A company is running a production database on Amazon RDS for PostgreSQL. The database experiences high read traffic from multiple application servers. Which data store management strategy would reduce the load on the primary database instance?

Accepted Answer

Create an RDS Read Replica in the same region.. Creating an RDS Read Replica in the same region offloads read-heavy traffic from the primary PostgreSQL instance by providing a separate, read-only copy of the database. Application servers can direct SELECT queries to the Read Replica, reducing the primary instance's CPU and I/O load without affecting write performance. This is the most direct and cost-effective strategy for scaling read capacity in Amazon RDS for PostgreSQL.

Answer

Enable DynamoDB Accelerator (DAX) for the database.

Answer

Enable Multi-AZ deployment for automatic failover.

Answer

Use Amazon ElastiCache to cache query results.

Question 9

A data engineer is troubleshooting an Amazon DynamoDB table that has frequent throttling exceptions for write requests. The table has auto scaling enabled. What is the most likely cause?

Accepted Answer

The partition key is causing a hot partition. Auto scaling adjusts capacity based on utilization, but it cannot prevent throttling caused by a hot partition. If a single partition key value receives a disproportionate share of write traffic, that partition's throughput limit (3,000 WCU or 10 MB per partition) is exceeded, triggering ProvisionedThroughputExceededException. Auto scaling operates at the table level, not per partition, so it cannot resolve this imbalance.

Answer

The table's read capacity is set too low

Answer

The table's auto scaling is disabled

Answer

The table is using global tables without conflict resolution

Question 10

A company needs to encrypt data in transit between an EC2 instance and an S3 bucket. Which method should be used?

Accepted Answer

Use HTTPS endpoints. HTTPS endpoints encrypt data in transit between EC2 and S3 using TLS/SSL, ensuring confidentiality and integrity over the public internet. S3 supports HTTPS natively on its REST endpoints, and the AWS SDKs default to HTTPS, making this the simplest and most secure method for encrypting data in motion.

Answer

Use plain HTTP

Answer

Use an IPsec VPN

Answer

Server-side encryption (SSE)

Question 11

A data engineer is designing a data lake on Amazon S3 that must comply with a regulatory requirement to prevent any data from being overwritten or deleted for 7 years after creation. Which S3 feature should be used?

Accepted Answer

S3 Object Lock with retention mode set to COMPLIANCE. S3 Object Lock with retention mode set to COMPLIANCE ensures that objects cannot be overwritten or deleted for the specified retention period (7 years). The retention period cannot be shortened or removed by any user, including the root user, making it suitable for regulatory compliance. Option A is incorrect because a bucket policy that denies s3:DeleteObject can be modified or removed, and it does not prevent overwrites. Option B is incorrect because MFA Delete requires an additional authentication factor but can still be disabled by an authorized user, and it does not enforce a retention period. Option D is incorrect because bucket versioning alone does not prevent deletion; it only creates delete markers, and objects can still be permanently deleted.

Answer

S3 bucket policy that denies s3:DeleteObject

Answer

S3 bucket versioning with MFA Delete

Answer

S3 bucket versioning only

Question 12

A company uses AWS DMS to migrate an on-premises PostgreSQL database to Amazon RDS for PostgreSQL. After initial load, ongoing replication is set up. The replication task shows 'Task status: failed with error: The specified LSN is not available in the source database logs.' What is the most likely cause?

Accepted Answer

The source database's WAL retention period is too short, and required logs have been purged.. The error 'The specified LSN is not available in the source database logs' indicates that AWS DMS is trying to read a Write-Ahead Log (WAL) position that has already been purged. PostgreSQL sources require sufficient WAL retention to allow DMS to catch up during ongoing replication (CDC). If the WAL segments are recycled or removed before DMS reads them, the replication task fails with this specific LSN error.

Answer

DMS does not support PostgreSQL as a source for ongoing replication.

Answer

The source database's network security group blocks outbound traffic to DMS.

Answer

The full load was incomplete, preventing CDC from starting.

Question 13

A data engineer is migrating an on-premises Apache Cassandra cluster to Amazon Keyspaces (for Apache Cassandra). The cluster has 10 TB of data. The migration must minimize application downtime. Which strategy should the engineer use?

Accepted Answer

Set up a dual-write pattern where the application writes to both the on-premises cluster and Keyspaces, then switch reads to Keyspaces once data is synchronized.. The dual-write pattern allows the application to write to both the on-premises Cassandra cluster and Amazon Keyspaces simultaneously, ensuring data consistency with minimal downtime. Once the existing data is backfilled and the systems are synchronized, reads can be switched to Keyspaces with near-zero application interruption. This approach avoids the downtime required for bulk export/import or snapshot restore.

Answer

Export the data using the Cassandra COPY command and import it into Keyspaces using the COPY command.

Answer

Take a snapshot of the on-premises cluster and restore it to Keyspaces using the Keyspaces console.

Answer

Use AWS Database Migration Service (DMS) to continuously replicate data from the on-premises cluster to Keyspaces.

Question 14

A company is using Amazon S3 to store large amounts of archival data. The data is accessed infrequently but must be immediately retrievable when needed. Which storage class is the most cost-effective choice?

Accepted Answer

S3 Standard-IA. S3 Standard-IA (Infrequent Access) is the most cost-effective choice because it offers lower storage costs than S3 Standard while still providing millisecond first-byte latency for immediate retrieval. The data is accessed infrequently but requires instant availability, which matches the IA use case exactly.

Answer

S3 Standard

Answer

S3 Glacier Deep Archive

Answer

S3 Intelligent-Tiering

Question 15

A company uses Amazon S3 to store sensitive financial data. The security team requires that all objects be encrypted at rest using AWS KMS with a customer-managed key. Additionally, they want to audit all KMS decrypt calls for compliance. Which configuration should be used to meet these requirements?

Accepted Answer

Use SSE-KMS with a customer-managed KMS key and enable CloudTrail data events for the key.. SSE-KMS with a customer-managed key allows the company to control the encryption key lifecycle and meet the requirement for customer-managed keys. Enabling CloudTrail data events for the KMS key captures all decrypt API calls, providing the necessary audit trail for compliance.

Answer

Enable default encryption on the bucket with SSE-KMS using an AWS managed key.

Answer

Use SSE-S3 with a bucket policy that denies uploads without encryption.

Answer

Use SSE-C with client-managed keys and log S3 API calls.