DBS-C01 Practice Test 20 — 15 Questions

Question 1

The exhibit shows the output of an AWS CLI command for an Amazon RDS DB instance. Based on the output, what is the current configuration of the DB instance?

Accepted Answer

It is a Single-AZ MySQL DB instance.. The CLI output shows a DBInstance (not a DBCluster), a single endpoint, no MultiAZ flag set to true, and no reader endpoint — all consistent with a Single-AZ MySQL DB instance. Aurora would show a DBClusterIdentifier and cluster endpoint, and a failed state would show status 'failed' rather than 'available'.

Answer

It is an Amazon Aurora MySQL-Compatible DB cluster.

Answer

It is a MySQL DB instance that is currently in a failed state.

Answer

It is a Multi-AZ DB instance with a standby in a different AZ.

Question 2

A database administrator notices that an Amazon RDS for MySQL DB instance has experienced a failover during a maintenance window. What is the most likely cause of this failover?

Accepted Answer

A system update was applied during the maintenance window, causing a reboot. During a maintenance window, AWS may apply mandatory OS or DB engine patches to an RDS instance. If the instance is configured for Multi-AZ, applying a system update triggers a reboot of the primary, which causes an automatic failover to the standby to minimize downtime. This is the standard, expected behavior for Multi-AZ deployments during maintenance.

Answer

The DB instance ran out of storage and automatically failed over

Answer

A read replica was promoted to a primary instance

Answer

A manual failover was initiated by the administrator

Question 3

A company uses Amazon DynamoDB to store IoT sensor data. Each sensor writes a record every second, and the application needs to query the last 24 hours of data for a specific sensor. The query must be very fast. Which table design and query pattern will minimize cost and latency?

Accepted Answer

Use a composite primary key: partition key = sensor ID, sort key = timestamp. Using a composite primary key with partition key = sensor ID and sort key = timestamp allows DynamoDB to efficiently query all items for a specific sensor in a single partition, using the Query API with a sort key condition on timestamp. This design ensures fast, targeted reads without scanning, minimizing read capacity units and latency.

Answer

Use a simple primary key (sensor ID) and scan the table filtering by timestamp

Answer

Use a composite primary key: partition key = timestamp, sort key = sensor ID

Answer

Use a simple primary key (sensor ID) and a global secondary index on timestamp

Question 4

A company is deploying a new Amazon RDS for MySQL database in a VPC. The database must be accessible only from an application server running in the same VPC. The security team also wants to ensure that the database is not accessible from the internet. Which TWO configurations are required? (Choose TWO.)

Accepted Answer

Configure the security group to allow inbound traffic only from the application server's security group.. Option C is correct because an RDS security group must explicitly permit inbound traffic on the database port (e.g., 3306 for MySQL), and referencing the application server's security group as the source restricts access to only that application server rather than an entire subnet or CIDR range. Option D is correct because setting the DB instance's PubliclyAccessible attribute to false ensures RDS does not assign a publicly resolvable DNS endpoint or allow internet-originated connections, keeping the instance reachable only from within the VPC. Option A is wrong because placing the DB in a public subnet does not by itself make it internet-accessible and is not required for same-VPC access; a private subnet is the recommended placement. Option B is wrong because DB parameter groups control engine-level settings, not network access. Option E is wrong because a network ACL denying 0.0.0.0/0 is not a required configuration and is unnecessary when the security group and PubliclyAccessible setting already block internet access.

Answer

Place the DB instance in a public subnet.

Answer

Modify the DB parameter group to restrict network access.

Answer

Configure a network ACL to deny inbound traffic from 0.0.0.0/0.

Question 5

A company has an Amazon RDS for MySQL DB instance that is running low on storage. The current allocated storage is 500 GB, and the free space is down to 10 GB. The database administrator wants to increase storage with minimal downtime. Which action should be taken?

Accepted Answer

Use the AWS Management Console to modify the DB instance and increase the allocated storage.. RDS supports modifying storage online with minimal downtime. Increasing allocated storage from 500 GB to, for example, 600 GB can be done via a modification to the DB instance. The instance remains available during the modification, though a brief performance impact may occur. Stopping the instance is unnecessary. Creating a snapshot and restoring would cause longer downtime. Waiting for autoscaling might not be quick enough if space is critically low.

Answer

Stop the DB instance, modify the allocated storage, and start the instance.

Answer

Create a snapshot of the current DB instance, restore it to a new larger instance, and point the application to the new endpoint.

Answer

Enable storage autoscaling and wait for the automatic increase.

Question 6

A company runs a critical e-commerce application on Amazon RDS for MySQL with Multi-AZ enabled. The database is 2 TB and uses General Purpose (gp2) storage. Recently, during peak hours, the application experienced a 5-minute outage. The CloudWatch logs show that the primary DB instance failed and an automatic failover occurred. However, the failover took 3 minutes, which is longer than the expected 1-2 minutes. The 'ReadLatency' and 'WriteLatency' metrics were elevated before the failure. The 'BurstBalance' metric was at 0% for the hour before the failure. The team suspects the issue is related to storage performance. What should the team do to prevent this issue in the future?

Accepted Answer

Change the storage type to Provisioned IOPS (io1).. The BurstBalance at 0% indicates the gp2 volume exhausted its burst credits, causing I/O throttling and increased latency, which likely contributed to the failover delay. Switching to Provisioned IOPS (io1) provides consistent performance and avoids burst credit exhaustion. Option A is wrong because increasing the DB instance class addresses compute capacity, not storage I/O. Option C is wrong because backup retention period does not affect storage performance. Option D is wrong because read replicas offload read traffic but do not improve write performance on the primary instance.

Answer

Increase the DB instance class to a larger size.

Answer

Increase the backup retention period to 35 days.

Answer

Create a read replica to offload read traffic.

Question 7

A company uses Amazon RDS for Oracle with a custom application that generates complex hierarchical queries using CONNECT BY. They want to migrate to Amazon Aurora to reduce licensing costs. Which migration strategy requires the fewest application changes?

Accepted Answer

Migrate to Amazon Aurora PostgreSQL and rewrite hierarchical queries to use recursive CTEs.. Aurora PostgreSQL supports recursive Common Table Expressions (CTEs) via the WITH RECURSIVE clause, which can be used to rewrite Oracle's CONNECT BY hierarchical queries with minimal application changes. This approach avoids the licensing costs of Oracle while preserving the hierarchical query logic, requiring only a syntax rewrite rather than a complete redesign. Aurora MySQL does not support CONNECT BY or recursive CTEs, making PostgreSQL the only Aurora engine that can handle this workload without significant application restructuring.

Answer

Use AWS Database Migration Service (DMS) to migrate directly to Aurora with no application changes.

Answer

Migrate to Amazon Aurora MySQL and use its hierarchical query features.

Answer

Migrate to Amazon RDS for SQL Server and use its recursive CTEs.

Question 8

A company is migrating an on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The database is 2 TB and has a sustained write rate of 150 MB/s. The migration must have minimal downtime. Which AWS service or tool should be used for the initial data load and ongoing replication?

Accepted Answer

Use AWS Database Migration Service (AWS DMS) with full load and ongoing replication. AWS DMS is the correct choice because it supports both a full load of the existing 2 TB database and ongoing change data capture (CDC) to replicate transactions with minimal downtime. DMS can handle sustained write rates of 150 MB/s by using appropriate instance sizing and tuning, and it provides built-in mechanisms for resumable loads and validation, which are critical for a large-scale migration with minimal downtime.

Answer

Use pg_dump and pg_restore

Answer

Use AWS Schema Conversion Tool (AWS SCT) to convert schema and AWS DMS for data migration

Answer

Use AWS S3 Transfer Acceleration to upload data to Amazon S3, then restore to RDS

Question 9

A database administrator runs the AWS CLI command shown in the exhibit. The administrator wants to enable encryption at rest for the RDS instance. What should the administrator do?

Accepted Answer

Take a snapshot of the DB instance, copy the snapshot with encryption enabled, and restore a new instance.. To enable encryption at rest for an existing unencrypted RDS instance, you cannot simply modify the instance to set StorageEncrypted to true. Instead, you must take a snapshot of the unencrypted instance, copy the snapshot with encryption enabled, and then restore a new instance from the encrypted snapshot. This is the only way to encrypt an existing unencrypted RDS instance.

Answer

Modify the DB instance and set StorageEncrypted to true.

Answer

Create a new KMS key and associate it with the DB instance.

Answer

Create a new DB parameter group with encryption enabled.

Question 10

A company is using Amazon RDS for SQL Server with Multi-AZ and automated backups enabled. The database administrator needs to restore the database to a specific point in time that is within the retention period. What is the correct procedure?

Accepted Answer

Use the RDS console to perform a point-in-time recovery to the desired time. The correct procedure for performing a point-in-time recovery within the retention period for an Amazon RDS for SQL Server instance with Multi-AZ and automated backups is to use the RDS console or API to specify the desired point in time. This restores the database to the specified time using the automated backup logs. Option B is incorrect because manual snapshots capture a specific point and cannot be used for arbitrary point-in-time recovery. Option C is incorrect because native SQL Server backup is not supported for RDS instances; AWS manages backups. Option D is incorrect because restoring from the latest automated snapshot does not give a specific point in time.

Answer

Restore from a manual snapshot taken at the desired time

Answer

Use the native SQL Server backup and restore functionality

Answer

Restore from the latest automated snapshot

Question 11

A database specialist is monitoring an Amazon RDS for SQL Server DB instance using Amazon CloudWatch. The specialist notices that the FreeStorageSpace metric is decreasing rapidly, and the instance is approaching its storage limit. The specialist needs to identify the cause of the rapid storage consumption. Which action should the specialist take to diagnose the issue?

Accepted Answer

Query the sys.dm_db_file_space_usage and sys.dm_db_log_space_usage DMVs to check space usage by file and log.. The DMVs sys.dm_db_file_space_usage and sys.dm_db_log_space_usage provide granular details about space usage within database files and transaction logs. They can pinpoint which database or log is growing, such as due to a large transaction or insufficient log backups. This is the most direct way to diagnose rapid storage consumption on RDS for SQL Server.

Answer

Check the CloudWatch metric DiskQueueDepth to see if there is a backlog of disk operations.

Answer

Review the RDS event log for messages about storage autoscaling being triggered.

Answer

Enable RDS Enhanced Monitoring and analyze the disk I/O metrics to identify high write activity.

Question 12

A company uses Amazon ElastiCache for Redis to cache session data for a high-traffic web application. The operations team notices that the cache hit rate has dropped from 95% to 70% over the past week, leading to increased latency. They suspect that many keys are expiring prematurely or being evicted. The Redis cluster is running in cluster mode with 3 shards. Which action should the team take to determine the cause of the reduced hit rate?

Accepted Answer

Analyze the KeyspaceHits and KeyspaceMisses metrics in CloudWatch, and compare with Evictions and ExpiredKeys.. The most effective way to diagnose a drop in cache hit rate is to examine CloudWatch metrics that directly measure hits and misses (KeyspaceHits, KeyspaceMisses) alongside metrics that explain key removal (Evictions, ExpiredKeys). This combination reveals whether the issue is due to memory pressure causing evictions or TTLs causing expirations, enabling targeted remediation.

Answer

Review the ElastiCache event log for messages about failed key lookups.

Answer

Use the Redis MONITOR command to capture all commands in real time and look for patterns of key access.

Answer

Check the Evictions and CurrConnections metrics in Amazon CloudWatch for each node.

Question 13

An IAM policy is attached to a user. What is the effect of this policy on the user's ability to delete the DB instance named prod-db?

The policy is:

```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": "rds:DeleteDBInstance",
      "Resource": "arn:aws:rds:us-east-1:123456789012:db:prod-db"
    },
    {
      "Effect": "Allow",
      "Action": "rds:*",
      "Resource": "*"
    }
  ]
}
```

Accepted Answer

The user cannot delete the DB instance because the Deny statement explicitly denies it.. AWS IAM evaluates policies with an explicit-deny-wins rule: if any statement in any applicable policy has Effect: Deny for the action/resource, the request is denied regardless of any Allow statements. Here, the Deny statement targets rds:DeleteDBInstance on the specific ARN of prod-db, so the user cannot delete that instance even though a broader Allow exists.

Answer

The user can delete the DB instance only after creating a final snapshot.

Answer

The user can delete the DB instance because the Allow statement grants all actions.

Answer

The user can delete the DB instance because the Allow statement is broader and applies to all resources.

Question 14

A company is planning to migrate a 1 TB MySQL database from on-premises to Amazon RDS for MySQL. The migration must have minimal downtime and support ongoing replication. Which THREE steps should the company include in the migration plan? (Choose THREE.)

Accepted Answer

Set up an AWS Direct Connect or VPN connection between on-premises and AWS.. A stable, low-latency network connection (Direct Connect or VPN) is essential for AWS DMS to perform ongoing replication with minimal downtime. Without this, the replication can be interrupted by network issues, causing data loss or extended cutover windows.

Answer

Deploy an Amazon EC2 instance to act as a proxy for the DMS replication.

Answer

Install the AWS Schema Conversion Tool on the source server to convert the schema.

Question 15

A company is running an Amazon DynamoDB table with on-demand capacity mode. The table experiences occasional throttling during peak hours. The application team wants to understand the read/write patterns to optimize the table design. Which approach should the database specialist take to analyze the throttling events?

Accepted Answer

Enable CloudWatch Contributor Insights for DynamoDB to identify throttled requests.. CloudWatch Contributor Insights for DynamoDB is specifically designed to analyze the most frequently accessed and throttled items in a DynamoDB table, providing detailed visibility into which partition keys or items are causing throttling. It aggregates data at the item level and helps identify hot partitions or heavy hitters, which is exactly what the team needs to optimize table design. This is the recommended tool for diagnosing throttling patterns in on-demand mode.

Answer

Enable DynamoDB Accelerator (DAX) to cache reads and reduce throttling.

Answer

Use AWS CloudTrail to log all DynamoDB API calls and analyze the logs.

Answer

Switch to provisioned capacity mode with auto scaling to handle the spikes.