The answer is CodeDeployDefault.OneAtATime because it minimizes the number of instances taken out of service at any given moment, deploying to only one EC2 instance at a time while the remaining three continue serving traffic. This predefined deployment configuration is ideal for critical applications requiring zero downtime, as it ensures that the Auto Scaling group’s capacity is never reduced by more than one instance, preserving availability across both Availability Zones. On the AWS Certified Developer Associate DVA-C02 exam, this question tests your understanding of how CodeDeploy’s deployment configurations map to availability and speed trade-offs—a common trap is choosing CodeDeployDefault.AllAtOnce for speed, which would cause downtime by updating all four instances simultaneously. For a quick memory tip, think “One at a time keeps the service line fine”—the key is that OneAtATime prioritizes availability over deployment speed, making it the safest choice for production workloads with strict uptime requirements.
DVA-C02 Deployment Practice Question
This DVA-C02 practice question tests your understanding of deployment. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. A key principle to apply: codeDeployDefault.OneAtATime updates one instance at a time in a deployment group.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A developer is using AWS CodeDeploy to deploy an application to an Auto Scaling group of EC2 instances. The application is critical and must have zero downtime. The Auto Scaling group currently has 4 instances spread across 2 Availability Zones. Which predefined deployment configuration minimizes the number of instances taken out of service at any given time?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
CodeDeployDefault.OneAtATime
Option C, CodeDeployDefault.OneAtATime, is correct because it deploys the application to only one instance at a time, ensuring that the remaining instances continue to serve traffic. This minimizes the number of instances taken out of service at any given moment, which is critical for achieving zero downtime in an Auto Scaling group with 4 instances across 2 Availability Zones.
Key principle: CodeDeployDefault.OneAtATime updates one instance at a time in a deployment group.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
CodeDeployDefault.AllAtOnce
Why it's wrong here
AllAtOnce deploys to all instances simultaneously, taking the entire fleet out of service and causing downtime.
✗
CodeDeployDefault.HalfAtATime
Why it's wrong here
HalfAtATime deploys to half (2) of the instances at a time, which still takes a significant portion of capacity out.
✓
CodeDeployDefault.OneAtATime
Why this is correct
OneAtATime deploys to a single instance at a time, minimizing the number of instances offline and best preserving availability.
Related concept
CodeDeployDefault.OneAtATime updates one instance at a time in a deployment group.
✗
CodeDeployDefault.LambdaCanary10Percent5Minutes
Why it's wrong here
This configuration is designed for Lambda functions, not EC2 instances, and is not applicable here.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse deployment configurations designed for EC2 instances (like OneAtATime) with those for Lambda (like LambdaCanary10Percent5Minutes), or incorrectly assume HalfAtATime is the safest option without considering that OneAtATime minimizes the number of instances out of service even further.
Detailed technical explanation
How to think about this question
CodeDeploy's predefined deployment configurations for EC2/on-premises compute platforms control the traffic shifting and instance batch size. OneAtATime uses a batch size of 1, meaning only one instance is stopped, updated, and re-registered with the load balancer before proceeding to the next. This approach is ideal for stateful applications or when maintaining full capacity during deployment is critical, as it keeps 75% of instances serving traffic at all times in a 4-instance group.
KKey Concepts to Remember
CodeDeployDefault.OneAtATime updates one instance at a time in a deployment group.
It is ideal for minimizing downtime and maintaining high availability during deployments.
This configuration ensures a minimal reduction in application capacity during updates.
It is suitable for critical applications where service interruption must be avoided.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
CodeDeployDefault.OneAtATime updates one instance at a time in a deployment group.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Review codeDeployDefault.OneAtATime updates one instance at a time in a deployment group., then practise related DVA-C02 questions on the same topic to reinforce the concept.
Deployment — This question tests Deployment — CodeDeployDefault.OneAtATime updates one instance at a time in a deployment group..
What is the correct answer to this question?
The correct answer is: CodeDeployDefault.OneAtATime — Option C, CodeDeployDefault.OneAtATime, is correct because it deploys the application to only one instance at a time, ensuring that the remaining instances continue to serve traffic. This minimizes the number of instances taken out of service at any given moment, which is critical for achieving zero downtime in an Auto Scaling group with 4 instances across 2 Availability Zones.
What should I do if I get this DVA-C02 question wrong?
Review codeDeployDefault.OneAtATime updates one instance at a time in a deployment group., then practise related DVA-C02 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
CodeDeployDefault.OneAtATime updates one instance at a time in a deployment group.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A developer is using AWS CodeDeploy to deploy an application to a fleet of EC2 instances in an Auto Scaling group. The application must remain available during the deployment. The developer wants to update one instance at a time, ensuring that only one instance is taken offline at any moment. Which deployment configuration should the developer choose?
medium
✓ A.CodeDeployDefault.OneAtATime
B.CodeDeployDefault.HalfAtATime
C.CodeDeployDefault.AllAtOnce
D.CodeDeployDefault.LambdaCanary10Percent5Minutes
Why A: CodeDeployDefault.OneAtATime is the correct deployment configuration because it deploys the application to only one instance at a time, ensuring that the remaining instances continue to serve traffic. This matches the requirement to take only one instance offline at any moment, preserving high availability throughout the deployment.
Variation 2. A developer is using AWS CodeDeploy to deploy an application to an Auto Scaling group. The deployment is configured with a 'OneAtATime' deployment configuration. The developer notices that the deployment is taking a long time. What is the most likely reason?
easy
A.The deployment group is configured with an incorrect load balancer.
✓ B.The Auto Scaling group has a large number of instances, and deploying one at a time is slow.
C.The deployment configuration is set to 'AllAtOnce', but the developer intended 'OneAtATime'.
D.The CodeDeploy agent on the instances is not running.
Why B: Option C is correct because 'OneAtATime' deploys to one instance at a time, which can be slow for large groups. Option A is wrong because the deployment configuration is correct. Option B is wrong because the agent is not the issue. Option D is wrong because the deployment group is correctly configured.
Variation 3. A developer is using AWS CodeDeploy to deploy an application to an EC2 Auto Scaling group. The deployment must follow a rolling update, deploying to exactly 50% of the instances at a time. Which built-in deployment configuration should the developer use?
medium
A.CodeDeployDefault.OneAtATime
✓ B.CodeDeployDefault.HalfAtATime
C.CodeDeployDefault.AllAtOnce
D.CodeDeployDefault.LambdaAllAtOnce
Why B: Option B, CodeDeployDefault.HalfAtATime, is correct because it instructs CodeDeploy to deploy to exactly 50% of the instances in the Auto Scaling group at a time during a rolling update. This built-in configuration ensures that half the instances are updated before the other half, matching the requirement for a 50% rolling deployment.
Variation 4. A developer is using AWS CodeDeploy to deploy an application to an EC2 Auto Scaling group. The deployment must ensure that a minimum number of instances are always running and healthy. The developer wants to deploy to 10 instances. Which deployment configuration should the developer use?
hard
✓ A.CodeDeployDefault.OneAtATime
B.CodeDeployDefault.AllAtOnce
C.CodeDeployDefault.HalfAtATime
D.CodeDeployDefault.MinHealthyHostsPercentage: 90
Why A: Option A, CodeDeployDefault.OneAtATime, is correct because it ensures that only one instance is updated at a time, which guarantees that a minimum number of instances (9 out of 10) remain healthy and running throughout the deployment. This configuration is ideal for maintaining high availability and meeting strict uptime requirements.
Variation 5. A developer is using AWS CodeDeploy to deploy an application to an Auto Scaling group. The deployment must be as fast as possible while ensuring that at least 50% of instances remain healthy throughout. Which deployment configuration should be used?
hard
A.CodeDeployDefault.OneAtATime
✓ B.CodeDeployDefault.HalfAtATime
C.CodeDeployDefault.AllAtOnce
D.CodeDeployDefault.MinHealthyPercent
Why B: CodeDeployDefault.HalfAtATime is the correct choice because it deploys to half of the instances in the Auto Scaling group at a time, ensuring that at least 50% of instances remain healthy throughout the deployment. This configuration balances speed (by deploying to multiple instances concurrently) with the required availability constraint, making it the fastest option that satisfies the 'at least 50% healthy' requirement.
Variation 6. A developer is using AWS CodeDeploy to deploy an application to an EC2 Auto Scaling group. The application must remain fully available; only one instance should be taken offline at a time. The developer wants to configure the deployment to update instances one by one, ensuring that the deployment fails fast if any instance fails to deploy. Which deployment configuration should the developer choose?
medium
A.CodeDeployDefault.AllAtOnce
B.CodeDeployDefault.HalfAtATime
✓ C.CodeDeployDefault.OneAtATime
D.CodeDeployDefault.BlueGreen
Why C: Option C, CodeDeployDefault.OneAtATime, is correct because it deploys the application to one instance at a time, ensuring that only one instance is taken offline during the deployment. This satisfies the requirement for the application to remain fully available. Additionally, this configuration fails fast: if any instance fails to deploy, the deployment stops immediately, preventing further instances from being updated.
Last reviewed: Jun 11, 2026
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