DBS-C01 Practice Test 17 — 15 Questions

Question 1

A company runs an application that requires a relational database with high availability across multiple Availability Zones. The database must automatically failover with minimal downtime. Which AWS service meets these requirements?

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

Accepted Answer

Amazon RDS for MySQL with Multi-AZ deployment.. Amazon RDS for MySQL with Multi-AZ deployment automatically provisions and maintains a synchronous standby replica in a different Availability Zone. If the primary instance fails, Amazon RDS automatically fails over to the standby, typically within 60–120 seconds, providing high availability with minimal downtime. This meets the requirement for a relational database with automatic failover across multiple Availability Zones.

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Amazon DynamoDB with global tables.

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Amazon Redshift with cross-Region snapshots.

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Amazon RDS for MySQL with a single instance.

Question 2

A company needs to deploy a globally distributed application with a database that supports multi-region writes and automatic conflict resolution. Which AWS database service should be used?

Accepted Answer

Amazon DynamoDB Global Tables. Amazon DynamoDB Global Tables is the correct choice because it provides a fully managed, multi-Region, multi-active database that replicates data across AWS Regions with automatic conflict resolution using last-writer-wins (LWW) or application-defined conflict resolution. This directly meets the requirement for multi-region writes and automatic conflict resolution without requiring custom replication logic.

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Amazon Aurora Global Database

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Amazon RDS for MySQL with Multi-AZ

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Amazon ElastiCache for Redis

Question 3

A database administrator is troubleshooting a failover event for an Amazon RDS for SQL Server Multi-AZ DB instance. The failover occurred automatically. Which AWS service or feature should the administrator use to view the failover history and the reason for the failover?

Accepted Answer

The Amazon RDS console Events page.. The Amazon RDS console Events page stores RDS events, including failover events with reasons. This is the best place to view failover history and reason. CloudTrail records API calls but not internal failover reasons. CloudWatch Logs does not automatically log failover reasons. The AWS Status Dashboard shows service health, not instance-specific failover history.

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Amazon CloudWatch Logs for the DB instance.

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AWS CloudTrail logs to view the failover API call.

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The AWS Status Dashboard.

Question 4

A company wants to automate the creation of a new Amazon RDS for SQL Server instance with specific configurations, including VPC, subnet, and security group settings. Which AWS service should be used to deploy this infrastructure as code?

Accepted Answer

AWS CloudFormation. AWS CloudFormation is the correct service because it allows you to define your entire infrastructure, including Amazon RDS for SQL Server instances, VPCs, subnets, and security groups, as code using a JSON or YAML template. This enables automated, repeatable deployments and version control of your infrastructure, which is the core requirement for infrastructure as code (IaC).

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AWS CodeDeploy

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AWS Elastic Beanstalk

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AWS OpsWorks

Question 5

A database specialist manages an Amazon Aurora MySQL cluster used for an online ordering system. During peak traffic, the application reports occasional connection timeouts and slow queries. The specialist enables Performance Insights with a retention period of 7 days and observes that the wait event 'io/table/sql/handler' dominates during those periods. The cluster has one writer and one reader, both using db.r5.2xlarge instances. Which action should the specialist take to reduce the impact of this wait event?

Accepted Answer

Analyze the top SQL statements in Performance Insights and add appropriate indexes to reduce the number of rows scanned.. The dominant wait event 'io/table/sql/handler' points to I/O bottlenecks caused by inefficient SQL. Performance Insights provides detailed metrics to identify the top SQL statements contributing to the load. By analyzing these statements and adding suitable indexes or rewriting queries to reduce logical and physical reads, the specialist can lower I/O waits and improve response times. Instance scaling or parallel query may help in specific cases but do not directly resolve the underlying query inefficiency.

Answer

Enable the Aurora parallel query feature on the cluster to offload I/O processing to the storage layer.

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Increase the size of the Aurora cluster's buffer pool by scaling the writer instance to db.r5.4xlarge.

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Modify the Aurora cluster to use a larger instance class for the reader and redirect all read traffic to the reader.

Question 6

A gaming company uses Amazon DynamoDB to store player profiles. The table has partition key 'player_id' and sort key 'game_id'. During a new game launch, write traffic to a subset of players (influencers) spikes, causing throttling. The table uses on-demand capacity. Which solution resolves the hot key issue?

Accepted Answer

Add a random suffix to the partition key for the hot players to distribute writes. Adding a random suffix to the partition key for hot players distributes the write traffic across multiple partitions, preventing any single partition from being overwhelmed. DynamoDB's on-demand capacity mode automatically scales to handle traffic spikes, but it cannot resolve a hot key issue where all writes target the same partition key. By diversifying the partition key, writes are spread across partitions, allowing DynamoDB to utilize its full throughput capacity.

Answer

Increase the maximum read capacity units in the on-demand settings

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Switch to provisioned capacity mode and increase write capacity units

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Enable DynamoDB Accelerator (DAX) to cache writes

Question 7

A startup is building a social media application that requires a database to store user relationships (followers, following) and support graph queries. The data volume is expected to grow to tens of terabytes. Which AWS database service is most suitable for this workload?

Accepted Answer

Amazon Neptune.. Amazon Neptune is a fully managed graph database service optimized for storing and querying highly connected data, such as social media user relationships (followers, following). It supports both property graph and RDF models, enabling efficient graph traversal queries using Gremlin or SPARQL, which is ideal for this workload. Neptune scales to tens of terabytes and provides low-latency query performance for complex graph patterns, making it the most suitable choice.

Answer

Amazon RDS for MySQL with self-joins.

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Amazon Redshift.

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Amazon DynamoDB with adjacency list design.

Question 8

A developer notices that an Amazon ElastiCache for Redis cluster is experiencing high latency. The cluster uses a single node. Which CloudWatch metric should be reviewed first to determine if the issue is due to memory pressure?

Accepted Answer

DatabaseMemoryUsagePercentage. DatabaseMemoryUsagePercentage is the CloudWatch metric that reports the percentage of memory used by the Redis engine on the node. High values (approaching 100%) indicate memory pressure, which can trigger evictions, swap usage, or write failures, all of which cause latency. This is the first metric to review when diagnosing memory-related latency on a single-node ElastiCache for Redis cluster.

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NetworkBytesIn

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ReplicationLag

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CPUUtilization

Question 9

A startup is building a mobile application that needs to store user profiles and preferences. The data is schema-less and will grow rapidly. The application requires single-digit millisecond latency for reads and writes. Which AWS database should they choose?

Accepted Answer

Amazon DynamoDB. Amazon DynamoDB is a fully managed NoSQL key-value and document database that delivers single-digit millisecond latency at any scale. It is schema-less, making it ideal for storing user profiles and preferences that have varying attributes, and it automatically scales to handle rapid growth without downtime or performance degradation.

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Amazon Aurora (MySQL compatible)

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Amazon Redshift

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Amazon RDS for SQL Server

Question 10

A company uses an Amazon RDS for MySQL DB instance that needs to be accessed by a Lambda function. Which TWO steps should be taken to ensure secure access?

Accepted Answer

Create an IAM role for the Lambda function with permissions to use RDS IAM database authentication.. Option A is correct because RDS for MySQL supports IAM database authentication, which lets the Lambda function use a short-lived authentication token generated from an IAM role instead of a static password; the role must include the rds-db:connect permission for the DB user. Option B is correct because placing the Lambda function in the same VPC as the RDS instance allows private connectivity over the VPC network, so database traffic never traverses the public internet and security groups can tightly control access. Option C is not recommended because Lambda environment variables are not a secure secret store; credentials should be kept in AWS Secrets Manager or Systems Manager Parameter Store. Option D is wrong because using the master user for an application violates least privilege and increases blast radius if compromised. Option E is unnecessary and does not provide secure database access, since a NAT gateway only enables outbound internet traffic and is not needed for in-VPC RDS connectivity.

Answer

Store the database credentials in the Lambda environment variables.

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Use the database master user account for the Lambda function.

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Attach a NAT gateway to the Lambda function's VPC for outbound internet access.

Question 11

An IAM role with the above trust policy is created. The role is then attached to an EC2 instance. The application on the EC2 instance tries to create an RDS DB instance using the AWS SDK. What will happen?

Accepted Answer

The call will fail because the role's permissions policy does not allow rds:CreateDBInstance. The call will fail because the IAM role attached to the EC2 instance lacks a permissions policy (e.g., an identity-based policy) that explicitly grants the `rds:CreateDBInstance` action. The trust policy shown in the question only defines which principal (the EC2 service) can assume the role, not what actions the role can perform. Without a permissions policy allowing RDS operations, the SDK call is denied by default.

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The call will succeed because the trust policy grants permissions to EC2

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The call will succeed because the trust policy allows EC2 to create RDS instances

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The call will fail because the trust policy does not include the RDS service

Question 12

A company uses Amazon DynamoDB with on-demand capacity for a mobile application. During a marketing campaign, write traffic spikes to 10,000 writes per second for 5 minutes. The application experiences throttling after the first minute. The DynamoDB table has a single partition key. What should be done to prevent throttling in future campaigns?

Accepted Answer

Redesign the partition key to ensure write traffic is evenly distributed across partitions.. With on-demand capacity, DynamoDB automatically scales to handle traffic, but a single partition key creates a hot partition because all writes go to one partition, which has a maximum throughput limit (1,000 WCUs per partition). Even with on-demand, throttling occurs if the workload exceeds a single partition's capacity. Redesigning the partition key to distribute writes evenly across many partitions allows DynamoDB to scale horizontally and handle the 10,000 writes per second without throttling.

Answer

Enable DynamoDB Accelerator (DAX) to cache write requests.

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Switch to provisioned capacity and increase write capacity units to 10,000.

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Pre-warm the table by writing dummy data before the campaign.

Question 13

Arrange the steps to enable automated backups for an Amazon RDS for PostgreSQL DB instance in the correct order.

Accepted Answer

Modify the DB instance → Set backup retention period to a value greater than 0 → Apply the changes immediately → Confirm the modification. Automated backups are enabled by adjusting the backup retention period in the instance settings and applying the change.

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Set backup retention period to a value greater than 0 → Modify the DB instance → Apply the changes immediately → Confirm the modification

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Modify the DB instance → Apply the changes immediately → Set backup retention period to a value greater than 0 → Confirm the modification

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Confirm the modification → Modify the DB instance → Set backup retention period to a value greater than 0 → Apply the changes immediately

Question 14

Match each AWS database migration tool/service to its function.

Accepted Answer

AWS DMS: Migrates databases to AWS with minimal downtime. AWS DMS is for minimal-downtime database migration, AWS SCT for schema conversion, and AWS Snowball for physical data transfer. Common confusions involve swapping these functions.

Answer

AWS DMS: Converts database schema to target engine

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AWS Snowball: Migrates databases to AWS with minimal downtime

Question 15

A company is running a MongoDB-compatible workload on Amazon DocumentDB. They are experiencing high write latency during peak hours. The current cluster has one instance (db.r5.large) with 100 GB storage. Which change is most likely to improve write performance?

Accepted Answer

Increase the instance size to db.r5.xlarge. Increasing the instance size to db.r5.xlarge provides more CPU and memory resources, which directly improves the cluster's ability to handle write operations under load. In Amazon DocumentDB, write performance is primarily bound by the instance's compute capacity (vCPUs and memory) for processing write requests and managing the storage engine's buffer cache. A larger instance reduces contention and allows more concurrent writes to be processed efficiently.

Answer

Increase storage to 500 GB

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Enable Multi-AZ deployment

Answer

Add a read replica in a different Availability Zone