DOP-C02 Resilient Cloud Solutions Practice Test 9 — 15 Questions

Question 1

A company uses an NLB to distribute traffic to a fleet of EC2 instances in a single Availability Zone. During a recent AWS outage in that zone, the application became completely unavailable. The company wants to achieve high availability without rearchitecting the application. Which change is MOST appropriate?

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

Accepted Answer

Launch EC2 instances in a second Availability Zone and register them with the NLB target group. Registering EC2 instances in a second Availability Zone with the NLB target group allows NLB to route traffic to healthy instances across zones, providing high availability during a zone outage. Option A is incorrect because using a larger instance type and enabling detailed CloudWatch monitoring does not add redundancy across zones. Option B is incorrect because replacing NLB with an ALB still requires multi-AZ configuration to achieve high availability; cross-zone load balancing is already available on NLB. Option C is incorrect because scheduled scaling does not protect against zone failures; it only adjusts capacity predictably.

Answer

Use a larger instance type and enable detailed CloudWatch monitoring

Answer

Replace the NLB with an Application Load Balancer and enable cross-zone load balancing

Answer

Create an Auto Scaling group with a scheduled scaling policy to add instances during peak hours

Question 2

A company runs a containerized application on Amazon ECS with Fargate. The application needs to store session state. Which service provides the MOST resilient and scalable solution?

Accepted Answer

Amazon ElastiCache for Redis. Amazon ElastiCache for Redis provides a highly available, scalable, and low-latency in-memory data store ideal for session state management in a containerized environment. It supports replication and automatic failover, ensuring resilience. Option B (Amazon EFS) is a file storage service with higher latency and not designed for sub-millisecond session retrieval. Option C (ephemeral storage on the container instance) is not durable; data is lost when the container stops or fails. Option D (Amazon S3) is object storage with higher latency and not optimized for frequent read/write operations required for session state.

Answer

Amazon EFS

Answer

Ephemeral storage on the container instance

Answer

Amazon S3

Question 3

A company wants to ensure that its application running on AWS can withstand the failure of an entire AWS Region. Which TWO strategies should the company implement?

Accepted Answer

Deploy the application in multiple AWS Regions using an active-active or active-passive pattern. Option A is correct because deploying the application in multiple AWS Regions using an active-active or active-passive pattern ensures that if an entire Region fails, traffic can be served from another Region, providing true Region-level fault tolerance. Option C is correct because replicating data across Regions with services like DynamoDB global tables or RDS cross-Region replication ensures the application's data is available in the secondary Region, which is essential for the failover strategy in Option A to work. Option B is incorrect because multiple Availability Zones within a single Region only protect against AZ-level failures, not the failure of an entire Region. Option D is incorrect because a single CloudFront distribution with multiple origins in the same Region still depends on that one Region and does not survive a Region-wide outage. Option E is incorrect because RDS read replicas in the same Region remain within that Region and would be lost if the entire Region failed.

Answer

Deploy the application across multiple Availability Zones in a single Region

Answer

Use a single CloudFront distribution with multiple origins in the same Region

Answer

Configure RDS read replicas in the same Region

Question 4

A company runs a stateful web application on EC2 instances behind an ALB. The application stores session data in memory. The company wants to make the application stateless to improve resilience. Which TWO changes should the company make?

Accepted Answer

Disable sticky sessions on the ALB. To make the application stateless, the company should disable sticky sessions on the ALB (option B) and store session data in Amazon ElastiCache for Redis (option D). Disabling sticky sessions ensures that requests can be routed to any instance, and storing session data externally removes the dependency on in-memory state on individual instances, improving resilience. Option A is incorrect because increasing instance memory does not solve the statefulness issue. Option C is incorrect because enabling sticky sessions would maintain state on instances. Option E is incorrect because using an NLB does not address session state management.

Answer

Increase the instance memory to store more sessions

Answer

Enable sticky sessions (session affinity) on the ALB

Answer

Use an NLB instead of an ALB

Question 5

A company runs a production web application on EC2 instances behind an Application Load Balancer. The application experiences intermittent high latency. The operations team needs to identify the root cause without affecting live traffic. Which approach is the MOST efficient?

Accepted Answer

Enable detailed CloudWatch metrics on the ALB and analyze ALB access logs. Enabling detailed CloudWatch metrics on the ALB and analyzing ALB access logs provides visibility into request latency patterns without affecting live traffic. Option A is wrong because setting up a separate test environment does not directly help diagnose the current intermittent issue. Option B is wrong because SSHing into instances and running commands can impact production performance and does not provide historical latency data. Option D is wrong because tcpdump generates large packet captures that can degrade performance and requires significant analysis effort.

Answer

Deploy a separate test environment with identical configuration and run load tests

Answer

Enable EC2 detailed monitoring and SSH into each instance to run top and iostat

Answer

Run tcpdump on all EC2 instances and analyze packet captures

Question 6

A company uses AWS CodeDeploy for blue/green deployments to an Auto Scaling group. The deployment fails because the new instances do not pass health checks. The DevOps engineer discovers that the health check URL returns a 503 error. What is the MOST likely cause?

Accepted Answer

The target group health check path is '/health' but the application does not serve that endpoint. The health check URL returning a 503 error indicates that the application is not responding to the health check endpoint. Since the target group health check path is configured as '/health' but the application does not serve that endpoint, the ALB considers the instances unhealthy, causing CodeDeploy to fail the deployment. This is the most direct cause because the health check is failing at the application layer, not due to infrastructure issues.

Answer

The CodeDeploy agent on the new instances is not running

Answer

The security group for the ALB does not allow inbound traffic on port 80

Answer

The Auto Scaling group health check type is set to EC2 instead of ELB

Question 7

A company runs a stateless web application on a fleet of EC2 instances in an Auto Scaling group. The application stores session state in a shared ElastiCache Redis cluster. During traffic spikes, the application becomes slow. Monitoring shows that the Redis cluster has high CPU utilization. Which solution is MOST cost-effective and scalable?

Accepted Answer

Enable cluster mode on the ElastiCache Redis cluster and add more shards. Read replicas offload GET/SMEMBERS-type traffic from the primary, but every write must still be processed by the primary node, so if the workload has a significant write component, the primary's CPU and write path remain unchanged. Note: ElastiCache Redis read replicas do NOT require cluster mode — a cluster-mode-disabled replication group already supports up to 5 read replicas on a single shard. Cluster mode is only needed to add additional shards for horizontal write scaling, which is why option B (enabling cluster mode) is the more complete, scalable fix when the bottleneck may include writes.

Answer

Upgrade the Redis instance to a larger node type to handle more operations

Answer

Add read replicas to offload read traffic from the primary node

Answer

Migrate session state to DynamoDB with DAX for caching

Question 8

A company uses AWS CloudFormation to deploy infrastructure. The stack creation fails with the error: 'Resource handler returned message: 'The security group does not exist in VPC'.' The template references a security group by name. What is the MOST likely cause?

Accepted Answer

The security group name is misspelled or uses incorrect case. The error 'Resource handler returned message: The security group does not exist in VPC' occurs when CloudFormation cannot find a security group with the specified name in the target VPC. The most likely cause is a misspelling or case sensitivity issue (Option A), as CloudFormation matches security group names exactly. While region scoping (Option C) can also cause a similar error, the combination of a name-based reference and the specific error wording points to a name mismatch as the most common issue. IAM permission errors (Option B) would typically return an authorization error, not a 'does not exist' error. Option D is incorrect because a default VPC security group exists and would not cause this error unless it is missing, which is unlikely.

Answer

The IAM role used for CloudFormation does not have permissions to describe security groups

Answer

The stack is being created in a Region where the security group does not exist

Answer

The template uses a parameter that resolves to the default VPC security group

Question 9

A company wants to design a highly available and fault-tolerant architecture for a stateless web application on AWS. Which TWO actions should they take? (Choose two.)

Accepted Answer

Launch EC2 instances in at least two Availability Zones. To achieve high availability and fault tolerance for a stateless web application, you should deploy EC2 instances in at least two Availability Zones (C) to eliminate a single point of failure, and use an Auto Scaling group (E) to automatically replace failed instances and maintain desired capacity. Option A is incorrect because a single large instance is a single point of failure and does not provide fault tolerance. Option B is incorrect because multiple Application Load Balancers per AZ are unnecessary; a single ALB can route traffic across multiple AZs. Option D is incorrect because RDS Multi-AZ is a database feature, not for the web server fleet.

Answer

Use a single large EC2 instance to simplify management

Answer

Deploy multiple Application Load Balancers in each AZ

Answer

Use an RDS Multi-AZ deployment for the web server fleet

Question 10

An IAM policy is attached to an S3 bucket to allow access from a specific VPC CIDR range. However, users from the VPC are receiving 'Access Denied' errors when trying to access objects in the bucket. What is the MOST likely reason?

Accepted Answer

The condition key 'aws:SourceIp' evaluates the public IP address, but the VPC uses private IP addresses. The 'aws:SourceIp' condition key evaluates the source IP address of the request as seen by AWS, which is always a public IP address. When requests originate from within a VPC (e.g., from an EC2 instance), the source IP seen by S3 is the public IP of the instance or its NAT device, not the VPC's private CIDR range. Since the policy specifies a private VPC CIDR range using 'aws:SourceIp', it never matches the public source IP, resulting in 'Access Denied' errors.

Answer

The users are assuming an IAM role that does not have permission to access S3

Answer

The policy should use 'aws:sourceVpce' instead of 'aws:SourceIp' to restrict access to a VPC endpoint

Answer

The bucket policy requires HTTPS and the requests are using HTTP

Question 11

A DevOps engineer runs the above command and sees that one target is unhealthy with a 503 error. The application is a web server running on port 80. The health check is configured to hit the root path '/'. Which action should the engineer take to resolve the issue?

Accepted Answer

Verify that the application on the unhealthy instance is configured to respond to '/' with a 200 status code. The health check is configured to hit the root path '/' and expects a 200 status code. A 503 error indicates the application on the unhealthy instance is not serving the correct response for that path. Verifying that the application responds with a 200 status code on '/' directly addresses the root cause of the health check failure.

Answer

Change the health check port to 443 and use HTTPS

Answer

Increase the health check interval and timeout settings

Answer

Check the security group rules for the target group to ensure port 80 is open

Question 12

A company deploys the above CloudFormation stack. They want to enforce HTTPS for all requests to the S3 bucket. After deployment, users are still able to make HTTP requests. What is the problem?

Accepted Answer

The Deny statement's Resource specifies only the objects, not the bucket itself. The Deny statement in the bucket policy uses `arn:aws:s3:::example-bucket/*` as the Resource, which applies only to objects within the bucket, not to the bucket itself. To enforce HTTPS for all requests, including those to the bucket endpoint (e.g., `GET /` or `PUT /`), the Resource must also include the bucket ARN without the `/*` suffix. Without it, HTTP requests targeting the bucket itself (such as listing objects or configuring website hosting) are not denied, allowing HTTP access to bypass the policy.

Answer

The condition key 'aws:SecureTransport' is misspelled; it should be 'aws:SecureTransport' with a capital 'T'

Answer

The bucket is not versioned, so the policy does not apply to object versions

Answer

The policy uses Deny, but an Allow policy from another statement overrides it

Question 13

A company runs a critical web application on EC2 instances behind an Application Load Balancer. To improve resilience, they want to automatically replace failed instances. Which AWS service should they use?

Accepted Answer

Auto Scaling group with health checks. Auto Scaling groups with health checks automatically replace unhealthy instances based on ELB health check integration. Option D is correct. Option A (EC2 Instance Recovery) recovers instances on the same host but does not replace them if the host fails. Option B (Systems Manager Automation) requires manual or scheduled automation, not automatic health-based replacement. Option C (CloudFormation Stack update) does not provide auto-replacement; it manages infrastructure updates.

Answer

EC2 Instance Recovery

Answer

AWS Systems Manager Automation

Answer

CloudFormation Stack update

Question 14

A DevOps engineer needs to ensure that an application running on EC2 can automatically recover from an underlying hardware failure without manual intervention. Which AWS feature should be enabled?

Accepted Answer

Configure EC2 Auto Recovery with a CloudWatch alarm. EC2 Auto Recovery automatically recovers an instance when it becomes impaired due to underlying hardware failure, preserving its instance ID, private IP, and Elastic IP. Option A is incorrect because termination protection only prevents accidental deletion, not recovery. Option C is incorrect because an Auto Scaling group with a minimum size of 1 can replace a failed instance but launches a new instance rather than recovering the same one. Option D is incorrect because CloudWatch detailed monitoring provides more frequent metrics but does not trigger recovery actions.

Answer

Enable termination protection

Answer

Configure an Auto Scaling group with a minimum size of 1

Answer

Enable CloudWatch detailed monitoring

Question 15

A company is deploying a critical microservice on Amazon ECS with Fargate. They need to ensure that the service can tolerate an Availability Zone failure. What is the BEST approach?

Accepted Answer

Define the service to spread tasks across multiple Availability Zones. Amazon ECS with Fargate allows you to define a service with a 'spread across Availability Zones' strategy. By setting the service's placement strategy to spread tasks across multiple Availability Zones, the service automatically distributes tasks evenly across the specified AZs. If one AZ fails, the remaining tasks in other AZs continue to serve traffic, ensuring high availability. This is the most direct and effective method for tolerating an AZ failure in a Fargate-based deployment.

Answer

Use a cluster placement constraint to spread tasks across instances

Answer

Use EC2 launch type and spread tasks across instance types

Answer

Configure service auto scaling to add tasks when CPU is high