The answer is the 'CodeDeployDefault.AllAtOnce' configuration, which replaces all instances simultaneously, causing a temporary loss of database connectivity when the new application version introduces incompatible changes. This occurs because CodeDeploy deploys the new revision to every instance in the Auto Scaling group at the same time, so if the update includes a database schema mismatch, altered connection strings, or missing environment variables, all instances fail in unison, completely severing the database connection. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of deployment configuration blast radius and the trade-offs between speed and safety—a common trap is assuming any deployment failure is a network issue rather than recognizing the all-at-once strategy amplifies application-level faults. Memory tip: think "AllAtOnce = All Down at Once" to recall that simultaneous updates leave no healthy instances to maintain connectivity during a bad release.
DOP-C02 Configuration Management and IaC Practice Question
This DOP-C02 practice question tests your understanding of configuration management and iac. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 company uses AWS CodeDeploy to deploy a web application to an Auto Scaling group. The deployment fails because the new instances cannot connect to the database. The previous deployment succeeded. The DevOps engineer checks the CodeDeploy deployment configuration and finds that the deployment uses the 'CodeDeployDefault.AllAtOnce' configuration. What is the MOST likely cause of the failure?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The deployment replaced all instances at once, causing a temporary loss of connectivity if the new application version has incompatible changes.
The 'CodeDeployDefault.AllAtOnce' deployment configuration causes CodeDeploy to attempt to deploy the new application revision to all instances in the Auto Scaling group simultaneously. If the new application version contains incompatible changes—such as a database schema mismatch, altered connection strings, or missing environment variables—all instances will fail at the same time, resulting in a complete loss of connectivity to the database. This contrasts with a rolling or canary deployment, which would limit the blast radius by updating only a subset of instances at a time.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The load balancer health check is misconfigured, causing new instances to be deregistered.
Why it's wrong here
Health check misconfiguration would not affect database connectivity.
✗
The deployment group is not configured to handle traffic routing, causing a routing loop.
Why it's wrong here
AllAtOnce does not use traffic routing.
✗
The security group for the Auto Scaling group was updated during deployment, blocking database access.
Why it's wrong here
Security groups are not modified by CodeDeploy.
✓
The deployment replaced all instances at once, causing a temporary loss of connectivity if the new application version has incompatible changes.
Why this is correct
AllAtOnce can cause full outage if changes are not backward compatible.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume the failure is due to a misconfiguration (like security groups or health checks) rather than recognizing that the deployment strategy itself—replacing all instances at once—amplifies the impact of any application-level incompatibility.
Detailed technical explanation
How to think about this question
Under the hood, CodeDeploy's AllAtOnce strategy sets the 'MinHealthyHosts' to 0, meaning no instances need to remain healthy during the deployment. When the new application version has a breaking change—such as a different database driver or a required migration that hasn't been applied—all instances fail the deployment hooks (e.g., AfterInstall, ValidateService) simultaneously, leaving zero healthy instances. In a real-world scenario, this is why best practices recommend using a rolling deployment (e.g., CodeDeployDefault.OneAtATime) or a blue/green deployment to maintain availability during updates.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Configuration Management and IaC — This question tests Configuration Management and IaC — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The deployment replaced all instances at once, causing a temporary loss of connectivity if the new application version has incompatible changes. — The 'CodeDeployDefault.AllAtOnce' deployment configuration causes CodeDeploy to attempt to deploy the new application revision to all instances in the Auto Scaling group simultaneously. If the new application version contains incompatible changes—such as a database schema mismatch, altered connection strings, or missing environment variables—all instances will fail at the same time, resulting in a complete loss of connectivity to the database. This contrasts with a rolling or canary deployment, which would limit the blast radius by updating only a subset of instances at a time.
What should I do if I get this DOP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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