Quick Answer
The answer is CodeDeployDefault.OneAtATime, because this deployment configuration ensures that only a single instance in an Auto Scaling group is taken out of service at any given moment, directly meeting the requirement to limit the percentage of instances removed during a gradual rollout. Unlike percentage-based configurations, OneAtATime uses a fixed count of one instance, making it ideal for safe, incremental updates where you want to minimize risk and maintain high availability. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this question tests your understanding of how CodeDeploy deployment configurations interact with Auto Scaling groups—a common trap is confusing OneAtATime with percentage-based options like HalfAtATime or AllAtOnce, which would take more instances offline simultaneously. Remember that OneAtATime is the most conservative choice for gradual rollouts, and a simple memory tip is “One at a time, one instance offline at a time.”
This DOP-C02 practice question tests your understanding of sdlc automation. 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. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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 DevOps engineer wants to use AWS CodeDeploy to deploy an application to an Auto Scaling group. The deployment must ensure that only a certain percentage of instances are taken out of service at a time. Which deployment configuration supports this requirement?
CodeDeployDefault.OneAtATime
Takes out one instance at a time.
CodeDeployDefault.LambdaCanary10Percent5Minutes
Why wrong: For Lambda, not EC2/ASG.
CodeDeployDefault.AllAtOnce
Why wrong: Takes all instances out of service at once.
CodeDeployDefault.LambdaLinear10PercentEvery1Minute
Why wrong: For Lambda, not EC2/ASG.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
CodeDeployDefault.OneAtATime
CodeDeployDefault.OneAtATime is the correct deployment configuration because it ensures that only one instance in the Auto Scaling group is taken out of service at a time, which directly satisfies the requirement of limiting the percentage of instances removed during deployment. This configuration is designed for EC2/On-Premises deployments and uses a fixed number of instances (one) rather than a percentage, making it ideal for gradual, safe rollouts.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
CodeDeployDefault.OneAtATime
Why this is correct
Takes out one instance at a time.
Related concept
Read the scenario before looking for a memorised answer.
CodeDeployDefault.LambdaCanary10Percent5Minutes
Why it's wrong here
For Lambda, not EC2/ASG.
CodeDeployDefault.AllAtOnce
Why it's wrong here
Takes all instances out of service at once.
CodeDeployDefault.LambdaLinear10PercentEvery1Minute
Why it's wrong here
For Lambda, not EC2/ASG.
Common exam traps
The trap here is that candidates often confuse deployment configurations designed for Lambda functions (like Canary and Linear) with those for EC2/On-Premises, or they mistakenly think AllAtOnce limits the percentage of instances taken out of service, when in fact it takes all instances out at once.
Detailed technical explanation
Under the hood, CodeDeployDefault.OneAtATime works by deploying to one instance in the Auto Scaling group at a time, waiting for the deployment to succeed on that instance before proceeding to the next; if the deployment fails, it stops and rolls back, preventing cascading failures. This configuration is equivalent to a 'rolling update' with a batch size of 1, and it is often used in production environments where zero-downtime is critical, such as for stateful applications or databases. A subtle behavior is that CodeDeploy calculates the number of instances based on the current desired capacity of the Auto Scaling group, so if the group scales during deployment, the configuration adapts dynamically.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
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FAQ
SDLC Automation — This question tests SDLC Automation — Read the scenario before looking for a memorised answer..
The correct answer is: CodeDeployDefault.OneAtATime — CodeDeployDefault.OneAtATime is the correct deployment configuration because it ensures that only one instance in the Auto Scaling group is taken out of service at a time, which directly satisfies the requirement of limiting the percentage of instances removed during deployment. This configuration is designed for EC2/On-Premises deployments and uses a fixed number of instances (one) rather than a percentage, making it ideal for gradual, safe rollouts.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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