DOP-C02 Resilient Cloud Solutions — Timed 20 Questions

Question 1

A company uses DynamoDB global tables in two AWS Regions with strong consistency reads. They observe occasional write conflicts that are not being resolved automatically. The application uses DynamoDBMapper with optimistic locking. What should the DevOps engineer do to ensure conflict resolution?

20 minute time limit — choose an answer to begin.

Accepted Answer

Implement a custom conflict resolution using DynamoDB Streams and AWS Lambda.. DynamoDB global tables resolve conflicts automatically using last-writer-wins (LWW). However, if the application requires custom conflict resolution (e.g., to ensure only the latest version is applied or application-specific logic), LWW is insufficient. DynamoDB Streams can capture all updates, and a Lambda function can compare conflicting versions and apply the appropriate resolution. DynamoDBMapper's optimistic locking uses version attributes with conditional writes, but in global tables each replica may have a different version number; a conditional write in one region can succeed even if a newer write exists in another region, so it does not guarantee that the latest version wins.

Answer

Switch to eventual consistency reads to reduce conflicts.

Answer

Add a third global table region to increase redundancy.

Answer

Use conditional writes with a version number attribute to ensure updates are applied only to the latest version.

Question 2

A company's application runs on EC2 instances in a single Availability Zone. The operations team wants to improve resilience without redesigning the application. Which action is the MOST effective?

Accepted Answer

Deploy EC2 instances across multiple Availability Zones using an Auto Scaling group.. Deploying EC2 instances across multiple Availability Zones (AZs) using an Auto Scaling group is the most effective action because it eliminates the single point of failure at the AZ level. If one AZ experiences an outage, the Auto Scaling group automatically launches replacement instances in the remaining healthy AZs, ensuring application availability without requiring any application-level changes. This directly addresses the goal of improving resilience by leveraging AWS's fault-isolated infrastructure.

Answer

Use a larger instance type to handle more traffic.

Answer

Enable EC2 Auto Recovery to automatically restart the instance if it fails.

Answer

Place the instance in a placement group to ensure low latency.

Question 3

A company uses a third-party backup solution to back up its EC2 instances daily. The backups are stored in an S3 bucket with default settings. The company wants to ensure that backups are protected from accidental deletion and are available for at least one year. Which combination of S3 features should the DevOps engineer implement?

Accepted Answer

Enable S3 Object Lock with Governance mode and a retention period of 365 days, and set a lifecycle policy to transition to S3 Glacier Deep Archive after 30 days.. S3 Object Lock with Governance mode prevents objects from being deleted or overwritten by any user (including the root user) for the specified retention period of 365 days, meeting the one-year availability requirement. The lifecycle policy to transition to S3 Glacier Deep Archive after 30 days reduces storage costs while still keeping the data accessible for retrieval within 12 hours, which is acceptable for backup retention. This combination ensures immutability and cost-effective long-term storage.

Answer

Enable MFA Delete and set a lifecycle policy to transition to S3 Glacier after 30 days.

Answer

Enable versioning and set a lifecycle policy to expire noncurrent versions after 365 days.

Answer

Enable cross-Region replication to a bucket with versioning enabled.

Question 4

A company runs a microservices application on Amazon ECS with Fargate. The application includes a service that processes orders and stores them in an RDS PostgreSQL database. The company wants to ensure that the order service is resilient to AZ failures and can handle a sudden increase in order volume. Which TWO actions should the DevOps engineer take? (Choose TWO.)

Accepted Answer

Deploy the RDS instance in a Multi-AZ configuration.. Deploying the RDS instance in a Multi-AZ configuration provides automatic failover to a standby replica in a different Availability Zone, ensuring database resilience to AZ failures. Option D is correct because configuring the ECS service to run tasks in multiple Availability Zones distributes the order processing workload across AZs, improving both fault tolerance and scalability during sudden traffic spikes.

Answer

Increase the CPU and memory limits for the ECS task definition.

Answer

Place an Amazon CloudFront distribution in front of the order service.

Answer

Use RDS Proxy to manage database connections.

Question 5

A company's application uses Amazon DynamoDB as its primary data store. The application experiences occasional throttling errors during traffic spikes. The DevOps team needs to implement a solution that ensures consistent performance without manual intervention. Which TWO actions should the team take? (Choose TWO.)

Accepted Answer

Implement DynamoDB Accelerator (DAX) to cache read requests.. To handle occasional throttling during traffic spikes without manual intervention, the team should use DynamoDB Accelerator (DAX) to cache read requests, reducing read load on the table, and enable DynamoDB Auto Scaling to automatically adjust read and write capacity based on traffic patterns. DAX absorbs spikey read traffic, while Auto Scaling ensures sufficient capacity for writes and uncached reads, together providing consistent performance without manual scaling. Option E (On-Demand) also handles spikes automatically but can be costlier for predictable workloads; the combination of DAX and Auto Scaling is often more cost-effective for read-heavy applications.

Answer

Use eventually consistent reads for all queries.

Answer

Move the data to Amazon RDS with read replicas.

Answer

Switch DynamoDB to On-Demand capacity mode.

Question 6

A company runs a critical web application on Amazon EC2 instances behind an Application Load Balancer (ALB). The application uses an Amazon RDS for MySQL Multi-AZ DB instance for data storage. During an AWS infrastructure event, the primary Availability Zone (AZ) becomes unavailable, and the application experiences downtime. The RDS Multi-AZ failover completes automatically, but the application takes several minutes to reconnect. Which combination of actions would MOST reduce the recovery time for the application during such an event?

Accepted Answer

Use an RDS proxy (Amazon RDS Proxy) to pool and share database connections, and ensure the application uses the RDS cluster endpoint.. Amazon RDS Proxy maintains a warm connection pool to the database, so when the RDS Multi-AZ failover occurs, the proxy automatically reconnects to the new primary DB instance without requiring the application to re-establish connections. This eliminates the connection storm and the several-minute delay caused by the application's connection retry logic. The application must be configured to use the RDS Proxy endpoint (not the cluster endpoint) to benefit from this seamless failover.

Answer

Place all EC2 instances in a single AZ and use an Amazon Route 53 health check to reroute traffic to a standby environment in another AZ.

Answer

Deploy the RDS instance as a Single-AZ instance in the same AZ as the primary EC2 instances, and use read replicas for failover.

Answer

Configure an Application Load Balancer in front of the RDS instance to distribute connections across AZs.

Question 7

A company is designing a disaster recovery (DR) strategy for a stateless web application deployed on Amazon ECS with Fargate. The application is fronted by an Application Load Balancer (ALB) and uses Amazon ElastiCache for Redis for session state. The primary region is us-east-1. The DR plan requires a Recovery Point Objective (RPO) of 15 minutes and a Recovery Time Objective (RTO) of 30 minutes. Which solution meets these requirements with the LEAST operational overhead?

Accepted Answer

Deploy an ALB with a warm standby ECS service in us-west-2. Use Route 53 health checks to route traffic to the secondary region if primary fails. Use ElastiCache Global Datastore for Redis to replicate data across regions.. It uses ElastiCache Global Datastore for Redis, which provides cross-region replication with an RPO of seconds (well within 15 minutes) and automatic failover, minimizing operational overhead. The warm standby ECS service in us-west-2 with Route 53 health checks allows traffic to be redirected within the 30-minute RTO without manual intervention, as the ALB and ECS service are pre-provisioned.

Answer

Deploy an Active-Active configuration across two AWS regions using Route 53 latency routing. Use ElastiCache for Redis Global Datastore with multi-region writes.

Answer

Deploy a Pilot Light environment in us-west-2 with a scaled-down ECS service and Redis cluster. Use Route 53 DNS failover. On disaster, scale up the ECS service and promote the Redis cluster.

Answer

Use Amazon ECS with Fargate in us-east-1 only, and schedule daily snapshots of ElastiCache for Redis. In case of disaster, restore the snapshot in a new region and update DNS.

Question 8

A development team wants to ensure that their application can continue serving traffic even if an entire AWS Availability Zone (AZ) becomes unavailable. The application runs on Amazon EC2 instances in an Auto Scaling group and uses an Application Load Balancer (ALB). Which configuration should the team implement to meet this requirement?

Accepted Answer

Configure the Auto Scaling group to launch EC2 instances across multiple AZs, and ensure the ALB is enabled for cross-zone load balancing.. Deploying EC2 instances across multiple Availability Zones (AZs) ensures that if one AZ fails, the remaining AZs continue to serve traffic. Enabling cross-zone load balancing on the ALB distributes incoming requests evenly across all healthy instances in all AZs, preventing traffic from being sent only to instances in the same AZ as the client. This architecture meets the requirement for high availability and fault tolerance at the AZ level.

Answer

Use a launch template with multiple instance types to ensure diversity across the fleet.

Answer

Use a single AZ but configure EC2 Auto Scaling to replace unhealthy instances automatically.

Answer

Launch all EC2 instances in the same AZ to minimize latency, and configure the Auto Scaling group to maintain a minimum of two instances.

Question 9

A company runs a critical application on AWS using Amazon EC2 instances in an Auto Scaling group, an Application Load Balancer (ALB), and an Amazon RDS for PostgreSQL Multi-AZ DB cluster. The application must maintain an RTO of 5 minutes and an RPO of 1 second for database transactions. The current setup meets these requirements, but the DevOps team wants to improve the resilience of the application tier to withstand a regional failure. Which THREE actions should be taken? (Choose three.)

Accepted Answer

Replace the RDS Multi-AZ cluster with Amazon Aurora Global Database to replicate data across regions.. Amazon Aurora Global Database is the correct choice because it provides cross-region replication with a typical RPO of 1 second and RTO of 1 minute, meeting the stated requirements. Unlike standard RDS Multi-AZ, which is limited to a single region, Aurora Global Database replicates data asynchronously across multiple regions with minimal lag, ensuring the database tier can survive a regional failure while maintaining the required RPO of 1 second.

Answer

Use Amazon EFS Replication to replicate application data across regions with a recovery point objective (RPO) of 1 second.

Answer

Extend the existing Auto Scaling group to launch instances in two regions by specifying a second region in the launch template.

Question 10

A company runs a production e-commerce platform on AWS. The architecture includes an Application Load Balancer (ALB) that distributes traffic to a fleet of Amazon EC2 instances running in an Auto Scaling group across three Availability Zones (AZs). The application stores session state in Amazon ElastiCache for Redis (cluster mode disabled) with a single node. The database is an Amazon Aurora MySQL DB cluster with one writer and two reader instances in different AZs. The platform experiences intermittent slowdowns and occasional timeouts during peak traffic hours. The CloudWatch metrics show that the ALB's TargetResponseTime is elevated, and the Redis CPU utilization is consistently above 80% during these periods. The Auto Scaling group is scaling out, but new instances take several minutes to become healthy. The DevOps team has been asked to improve the resilience and performance of the application with minimal changes to the application code. Which solution should the team implement?

Accepted Answer

Migrate ElastiCache for Redis to a cluster mode enabled configuration with multiple shards and enable Multi-AZ with automatic failover. Also, use an ElastiCache replication group with read replicas in different AZs.. The primary bottleneck is the single-node Redis instance (CPU > 80%), which cannot scale horizontally and lacks high availability. Migrating to cluster mode enabled with multiple shards distributes CPU load across shards, while Multi-AZ with automatic failover and read replicas in different AZs provides high availability and read scaling. This directly addresses the elevated ALB TargetResponseTime caused by Redis latency. Note that the application will need to use a Redis Cluster-compatible client; since the stem allows minimal code changes, this solution is still appropriate.

Answer

Replace the ALB with a Network Load Balancer (NLB) to reduce latency, and use an Auto Scaling group with a step scaling policy based on Redis CPU utilization.

Answer

Increase the instance size of the ElastiCache for Redis node and the size of the Aurora writer instance. Also, increase the cooldown period for the Auto Scaling group to allow new instances to warm up.

Answer

Implement Amazon RDS Proxy in front of the Aurora cluster to reduce database connection overhead, and increase the size of the Redis instance to handle more connections.

Question 11

An AWS Lambda function that processes sensitive data writes objects to an S3 bucket. The security team requires that all objects be encrypted at rest using SSE-S3. The Lambda execution role uses the above IAM policy. Despite the policy, some objects are uploaded without server-side encryption. What is the most likely cause?

Accepted Answer

The Lambda function does not include the x-amz-server-side-encryption header in the PutObject request.. The IAM policy only allows the PutObject action when the request includes the `x-amz-server-side-encryption` header set to `AES256` (SSE-S3). If the Lambda function omits this header in its PutObject call, the request does not satisfy the IAM condition key `s3:x-amz-server-side-encryption`, and the policy denies the upload. However, the question states that objects are uploaded without encryption, which implies the policy is not being enforced as intended—likely because the Lambda function is not including the required header, and the bucket's default encryption or another mechanism is allowing the upload to succeed despite the policy.

Answer

The bucket has a default encryption policy that overrides the IAM policy.

Answer

The Lambda function is using a KMS key instead of SSE-S3.

Answer

The Lambda function is specifying a different encryption algorithm, such as aws:kms.

Question 12

Drag and drop the steps to troubleshoot a failed deployment in AWS CodeDeploy into the correct order.

Accepted Answer

Check CodeDeploy Console → Review Agent Logs → Validate AppSpec File → Verify Instance Configuration → Redeploy. Troubleshooting starts with console, then agent logs, then AppSpec, then instance configuration, then redeploy.

Answer

Review Agent Logs → Check CodeDeploy Console → Validate AppSpec File → Verify Instance Configuration → Redeploy

Answer

Validate AppSpec File → Check CodeDeploy Console → Review Agent Logs → Verify Instance Configuration → Redeploy

Answer

Redeploy → Check CodeDeploy Console → Review Agent Logs → Validate AppSpec File → Verify Instance Configuration

Question 13

Drag and drop the steps to perform a disaster recovery failover from a primary region to a secondary region using AWS Route 53 and RDS.

Accepted Answer

Configure health checks, then lower TTL, then promote RDS, then update DNS, then verify. First configure health checks, then lower TTL, then promote RDS, then update DNS, then verify.

Answer

Lower TTL, then configure health checks, then promote RDS, then update DNS, then verify

Answer

Configure health checks, then promote RDS, then lower TTL, then update DNS, then verify

Answer

Configure health checks, then update DNS, then lower TTL, then promote RDS, then verify

Question 14

Match each AWS CloudFormation concept to its description.

Accepted Answer

Change Set: A preview of how changes to a stack will be applied. Change Set previews stack changes; Stack is a resource collection; Stack Set manages stacks across accounts; Template is a JSON/YAML description.

Answer

Stack Set: A JSON or YAML text file that describes the infrastructure

Answer

Template: Allows you to create, update, or delete stacks across multiple accounts and regions

Question 15

Match each AWS CLI command to its function.

Accepted Answer

aws s3 sync: Syncs files to an S3 bucket. Correct matches: aws s3 sync syncs files to S3, aws ec2 describe-instances lists instances, aws cloudformation deploy deploys stacks, aws lambda invoke invokes functions. Common confusions arise from swapping these commands.

Answer

aws s3 sync: Deploys a CloudFormation stack

Answer

aws cloudformation deploy: Syncs files to an S3 bucket

Question 16

A company runs a critical web application on EC2 instances behind an Application Load Balancer (ALB). The application stores session state in an Amazon DynamoDB table. During a recent traffic spike, users experienced session timeouts and the application became unavailable. Which design change would BEST improve resilience?

Accepted Answer

Move session state to Amazon ElastiCache for Redis with cluster mode disabled.. Moving session state to ElastiCache for Redis offloads read/write operations from DynamoDB during traffic spikes, reducing the risk of throttling and session timeouts. While cluster mode disabled means a single node, it provides in-memory caching that improves performance and can be scaled up to handle increased load, making the application more resilient compared to relying solely on DynamoDB for session state during spikes. Option B is incorrect because DynamoDB is inherently multi-AZ, and global tables are for multi-region deployments, not for handling traffic spikes or throttling. Option C (adding a read replica) does not address write bottlenecks or session persistence. Option D (increasing EC2 instance sizes) does not resolve the session state storage issue.

Answer

Enable DynamoDB global tables or use a Multi-AZ deployment for the table.

Answer

Add a read replica to the DynamoDB table.

Answer

Increase the EC2 instance sizes to handle more traffic.

Question 17

A company runs a stateless web application on AWS Lambda behind an Application Load Balancer (ALB). During a deployment, the team updates the Lambda function to a new version. Some users report seeing the old version of the application for several minutes after the deployment. What is the MOST likely cause?

Accepted Answer

The ALB target group is still pointing to the old Lambda function version due to connection draining.. When an ALB is used with Lambda, the ALB invokes a specific Lambda function version or alias. If the deployment updates the Lambda function but the ALB target group alias is not updated atomically, or if connection draining keeps old connections active, some requests may still be routed to the old version. This can cause users to see the old application for several minutes. Option A is wrong because Lambda versions are immutable, so gradual rollout is not related. Option B is wrong because Lambda@Edge is not used in this setup (the application runs behind an ALB, not CloudFront). Option C is wrong because CloudFront is not mentioned in the architecture—the traffic goes directly from ALB to Lambda.

Answer

The Lambda function versions are not immutable, causing a gradual rollout.

Answer

Lambda@Edge is overriding the function version at the edge locations.

Answer

Amazon CloudFront is caching the old response and has not been invalidated.

Question 18

A company is designing a disaster recovery strategy for its primary RDS for PostgreSQL database in us-east-1. The RTO is 15 minutes and RPO is 1 minute. Which solution meets these requirements?

Accepted Answer

Create a cross-Region read replica in the secondary Region and promote it during failover.. A cross-Region read replica can be promoted to a primary instance in a matter of minutes, meeting the 15-minute RTO, and replication lag is typically under 1 minute, satisfying the 1-minute RPO. Option B (AWS Backup every hour) provides an RPO of up to 1 hour, exceeding the requirement. Option C (Multi-AZ in same region) does not provide cross-Region failover. Option D (manual snapshots every 5 minutes) has a higher RPO than 1 minute and may not be promotable quickly enough.

Answer

Use AWS Backup to copy automated backups to the secondary Region every hour.

Answer

Deploy a Multi-AZ RDS instance and failover to the standby in the same region.

Answer

Take manual snapshots of the database every 5 minutes and copy them to the secondary Region.

Question 19

A company runs a microservices application on Amazon ECS with Fargate launch type. The application experiences intermittent failures when calling an external API. The errors are transient and usually resolve within a few seconds. How should the company improve resilience?

Accepted Answer

Implement retry logic with exponential backoff in the application code.. Implementing retry logic with exponential backoff handles transient failures gracefully. Option A is wrong because increasing timeouts could worsen latency without addressing the root cause. Option C is wrong because scaling up (increasing tasks) does not help with external API failures. Option D is wrong because async processing adds complexity and does not directly address transient API failures.

Answer

Increase the timeout of the external API call to 60 seconds.

Answer

Increase the number of tasks in the ECS service to handle failures.

Answer

Use an Amazon SQS queue to decouple the API call from the application.

Question 20

A company uses AWS CloudFormation to deploy a multi-tier application. During an update, the stack fails and rolls back. The rollback also fails, leaving the stack in UPDATE_ROLLBACK_FAILED state. The operations team needs to resolve this with minimal disruption. What is the MOST efficient approach?

Accepted Answer

Use the 'ContinueUpdateRollback' API or AWS Management Console to retry the rollback.. 'ContinueUpdateRollback' is designed to retry a failed rollback, often fixing transient issues and bringing the stack to a consistent state. Option B is wrong because manually modifying resources is error-prone and not recommended; AWS provides automated rollback tools. Option C is wrong because deleting a stack in UPDATE_ROLLBACK_FAILED state can be problematic and may cause resource loss; it is not the most efficient approach. Option D is wrong because change sets are for updates, not for resolving rollback failures; a change set cannot be applied to a stack in UPDATE_ROLLBACK_FAILED state without first continuing the rollback.

Answer

Manually modify the resources to match the previous stack state.

Answer

Delete the stack and recreate it from the original template.

Answer

Execute a change set to update the stack to the desired configuration.