DOP-C02 Resilient Cloud Solutions — Timed 30 Questions

Question 1

A company runs a critical web application on EC2 instances behind an Application Load Balancer (ALB) with Auto Scaling. During a recent traffic spike, the application became unavailable for 10 minutes. Analysis shows that the ALB's healthy host count dropped to zero because the instances failed health checks due to high CPU load. What is the MOST effective design change to improve resilience during future traffic spikes?

Accepted Answer

Use predictive scaling with a scheduled scaling policy for known peak times.. Predictive scaling uses historical traffic data to forecast future demand and proactively adjust capacity before a spike occurs. This prevents the CPU from reaching critical levels that cause health check failures, ensuring the ALB always has healthy hosts. Scheduled scaling alone would not adapt to unexpected spikes, but predictive scaling combined with dynamic scaling provides both proactive and reactive resilience.

Answer

Increase the instance size to handle higher load.

Answer

Configure step scaling policies based on CPU utilization.

Answer

Set a higher CPU threshold for health checks.

Question 2

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?

Accepted Answer

Use conditional writes with a version number attribute to ensure updates are applied only to the latest version.. Option D is correct because DynamoDB global tables use last-writer-wins (LWW) for conflict resolution by default, but when using DynamoDBMapper with optimistic locking, the application must implement conditional writes with a version number attribute to ensure updates are applied only to the latest version. This prevents stale updates from overwriting newer data, as the conditional write will fail if the version number in the request does not match the current version in the table, allowing the application to retry with the updated version.

Answer

Implement a custom conflict resolution using DynamoDB Streams and AWS Lambda.

Answer

Switch to eventual consistency reads to reduce conflicts.

Answer

Add a third global table region to increase redundancy.

Question 3

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 4

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.. Option D is correct because 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 5

A company runs a stateful web application on EC2 instances behind a Network Load Balancer (NLB) in a single Availability Zone. The application stores session state locally on the instance. The company wants to achieve high availability across multiple AZs with minimal application changes. What should the DevOps engineer do?

Accepted Answer

Replace the NLB with an ALB and enable sticky sessions (session affinity) using the ALB's cookie.. Option D is correct because replacing the NLB with an ALB and enabling sticky sessions (session affinity) using the ALB's cookie allows the stateful web application to maintain session state across multiple AZs without modifying the application code. The ALB generates a cookie (AWSALB) that binds a client's session to a specific target instance, ensuring subsequent requests from the same client are routed to the same EC2 instance. This achieves high availability across AZs with minimal changes, as the application continues to store session state locally on the instance.

Answer

Add more AZs and configure the NLB with cross-zone load balancing.

Answer

Replace the NLB with an ALB and use ElastiCache for session storage.

Answer

Use a Multi-AZ RDS instance to store session state.

Question 6

A company's DevOps team is designing a disaster recovery plan for a critical application. The application runs on EC2 instances with an RDS MySQL database. The Recovery Time Objective (RTO) is 15 minutes, and the Recovery Point Objective (RPO) is 1 hour. Which approach BEST meets these requirements?

Accepted Answer

Use a warm standby strategy with a scaled-down copy of the production environment in the DR Region, and replicate data using RDS Multi-AZ with synchronous replication.. Option C is correct because a warm standby strategy with a scaled-down copy of the production environment in the DR Region, combined with RDS Multi-AZ using synchronous replication, meets the RTO of 15 minutes and RPO of 1 hour. Multi-AZ synchronous replication ensures zero data loss (RPO of seconds) and automatic failover within minutes, while the warm standby environment can be scaled up quickly to handle production traffic, satisfying the RTO.

Answer

Use backup and restore with daily snapshots stored in S3 and cross-Region replication.

Answer

Use a multi-Region application with Route 53 latency-based routing and RDS read replicas in the DR Region.

Answer

Use a pilot light strategy with EC2 instances stopped and RDS snapshots copied to the DR Region.

Question 7

A company's application uses Amazon SQS to decouple microservices. During peak hours, the SQS queue backlog grows significantly, causing processing delays. The DevOps team wants to reduce latency without increasing costs unnecessarily. What should the team do?

Accepted Answer

Configure Auto Scaling for the consumer fleet based on the ApproximateNumberOfMessagesVisible metric.. Option D is correct because scaling the consumer fleet based on the ApproximateNumberOfMessagesVisible metric directly addresses the backlog by adding more processing capacity when the queue grows. This approach reduces latency dynamically without incurring unnecessary costs during off-peak hours, as it only scales up when needed. Auto Scaling with SQS metrics is a cost-effective, elastic solution for handling variable workloads.

Answer

Increase the visibility timeout to allow consumers more time to process messages.

Answer

Use an SQS queue with priority settings to process high-priority messages first.

Answer

Increase the SQS queue's throughput by requesting a quota increase.

Question 8

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.. Option C is correct because 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 9

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.. DynamoDB Accelerator (DAX) is an in-memory cache that reduces read response times from milliseconds to microseconds, offloading read-heavy workloads from the DynamoDB table. By caching frequently accessed items, DAX absorbs traffic spikes and reduces the likelihood of throttling on read requests, ensuring consistent performance without manual intervention.

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 10

A company wants to design a highly available web application using AWS services. The application must be resilient to the failure of an entire AWS Region. Which THREE components should the architecture include? (Choose THREE.)

Accepted Answer

Amazon Route 53 with a failover routing policy.. Amazon Route 53 with a failover routing policy is correct because it enables DNS-based health checking and automatic traffic routing to a secondary region when the primary region becomes unavailable. This is essential for cross-region disaster recovery, as Route 53 can monitor endpoint health and update DNS records to direct users to the healthy region, ensuring application availability despite a full region failure.

Answer

An Application Load Balancer (ALB) deployed in one Region.

Answer

Amazon EC2 instances in a single Region.

Question 11

A company runs a critical e-commerce platform on AWS. The architecture includes an Application Load Balancer (ALB) that distributes traffic to a fleet of EC2 instances in an Auto Scaling group across three Availability Zones. The instances run a Java application that connects to an Amazon RDS Multi-AZ MySQL database. The application also uses Amazon ElastiCache for Redis for session caching. The company recently experienced a severe outage where the ALB's 5xx error rate spiked to 100% for 45 minutes. The root cause was a combination of a slow-running query on the RDS primary instance and a subsequent failover that caused the application to lose connections to the database. The failover happened because the slow query caused the primary to become unresponsive, triggering a Multi-AZ failover. During the failover, the application's connection pool exhausted, and new connections failed. The application logs show a high rate of 'java.sql.SQLTimeoutException' and 'com.mysql.cj.exceptions.CJCommunicationsException'. The DevOps team needs to implement a long-term solution that minimizes the impact of similar incidents. The solution must be cost-effective and require minimal application changes. Which combination of actions should the DevOps team take?

Accepted Answer

Implement Amazon RDS Proxy to manage database connections and add read replicas to offload read traffic.. Amazon RDS Proxy is the correct solution because it efficiently manages database connection pooling, reducing the likelihood of connection exhaustion during failovers. By maintaining a warm connection pool and automatically reconnecting to the new primary after a Multi-AZ failover, RDS Proxy minimizes application-side connection timeouts and errors like SQLTimeoutException and CJCommunicationsException. Adding read replicas offloads read traffic, reducing the load on the primary and mitigating the risk of slow queries causing unresponsiveness. This combination requires minimal application changes and is cost-effective compared to scaling the primary instance.

Answer

Use an Auto Scaling policy for EC2 based on RDS connection count and implement a read replica for the primary.

Answer

Configure Multi-AZ RDS with a synchronous standby and use Amazon RDS for MySQL with enhanced monitoring.

Answer

Increase the instance size of the RDS primary and enable Performance Insights to identify slow queries.

Question 12

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.. Option B is correct because 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. By using the RDS cluster endpoint (which points to the proxy), the application benefits from seamless failover and reduced latency during the DNS propagation of the new primary.

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 13

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.. Option A is correct because 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 14

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.. Option A is correct because 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 15

A company runs a containerized microservices application on Amazon EKS. The application includes a critical service that processes real-time financial transactions. This service must be highly available and resilient to node failures. The current setup uses a Deployment with 3 replicas and a ClusterIP service. During a recent node failure, the application experienced a brief period of unavailability. Which action should the DevOps engineer take to improve resilience without changing the underlying infrastructure?

Accepted Answer

Configure a PodDisruptionBudget with a maxUnavailable of 1, and add pod anti-affinity rules to spread pods across different nodes.. Option C is correct because a PodDisruptionBudget with maxUnavailable=1 ensures that at most one pod is unavailable during voluntary disruptions, while pod anti-affinity rules force the scheduler to distribute pods across different nodes. This combination prevents a single node failure from taking down all replicas, maintaining service availability without altering the underlying infrastructure.

Answer

Change the service type from ClusterIP to NodePort and configure an external load balancer.

Answer

Increase the number of replicas to 10 and use a node selector to schedule all pods on the largest instance type.

Answer

Enable HorizontalPodAutoscaler with a target CPU utilization of 50% to automatically scale the Deployment.

Question 16

A company is building a multi-tier web application on AWS. The application must be resilient to the failure of an entire Availability Zone. The architecture includes an Application Load Balancer (ALB), EC2 instances in an Auto Scaling group, and an Amazon RDS for MySQL database. Which TWO actions should be taken to achieve this resilience? (Choose two.)

Accepted Answer

Configure the Auto Scaling group to launch EC2 instances in at least two Availability Zones.. Option D is correct because configuring the Auto Scaling group to launch EC2 instances in at least two Availability Zones ensures that if one AZ fails, the remaining AZ(s) can continue serving traffic. This is a fundamental pattern for building AZ-resilient compute tiers. Option E is correct because deploying Amazon RDS for MySQL in a Multi-AZ configuration automatically provisions and maintains a synchronous standby replica in a different AZ, providing automatic failover if the primary DB instance fails, thus ensuring database resilience.

Answer

Configure an RDS read replica in a different Availability Zone.

Answer

Use a Single-AZ RDS for MySQL database to keep costs low.

Answer

Place all EC2 instances in the same Availability Zone to reduce cross-AZ data transfer costs.

Question 17

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 18

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.. Option D is correct because the primary bottleneck is the single-node Redis instance (CPU > 80%), which cannot scale reads or handle failover. Migrating to cluster mode enabled with multiple shards distributes the 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 without requiring application code changes.

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 19

A company runs a critical web application on Amazon EC2 instances behind an Application Load Balancer (ALB) across multiple Availability Zones. The application stores session data in a shared Amazon ElastiCache for Redis cluster. The operations team reports that during a recent AZ failure, users experienced session loss and application errors. Which combination of actions should the company take to improve resilience and maintain session state during an AZ failure? (Choose TWO.)

Accepted Answer

Configure the ALB with cross-zone load balancing enabled and connection draining set to a suitable timeout.. Option A is correct because enabling cross-zone load balancing on the ALB ensures traffic is distributed evenly across all EC2 instances in all AZs, and connection draining with a suitable timeout allows in-flight requests to complete before instances are deregistered, preventing session loss during an AZ failure. Option C is correct because enabling cluster mode for ElastiCache for Redis with replica nodes in different AZs provides automatic sharding and replication, ensuring session data remains available and consistent even if a primary node in one AZ fails.

Answer

Deploy an Auto Scaling group with a dynamic scaling policy that adds instances in the remaining AZs.

Answer

Configure the application to use a custom DNS name with a low TTL pointing to the ElastiCache cluster endpoint.

Answer

Enable Multi-AZ for the ElastiCache cluster to automatically fail over to a replica in another AZ.

Question 20

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.. Option A is correct because 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.