DOP-C02 SDLC Automation Practice Question
A company uses AWS CodeDeploy to deploy an application to an Auto Scaling group. The deployment fails with the error 'The overall deployment failed because too many individual instances failed deployment, too few healthy instances are available for deployment, or some instances in your deployment group are experiencing problems.' The deployment is set to 'AllAtOnce'. The application revision is a simple index.html. What is the most likely cause?
⚠ Common exam trap
Watch out — candidates often assume the error is due to S3 permissions or archive format, but the generic 'too many instances failed' message points to a fundamental agent connectivity issue, not a permissions or file format problem.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The CodeDeploy agent is not installed or running on the EC2 instances.
The error message indicates that too many instances failed deployment, which is typical when the CodeDeploy agent is not running on the EC2 instances. With an 'AllAtOnce' deployment, all instances are targeted simultaneously, so if the agent is missing on every instance, all will fail immediately, causing the overall deployment to fail. The simple index.html revision is not the issue; the agent is required to execute the AppSpec file and pull the revision from S3 or GitHub.
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 CodeDeploy agent is not installed or running on the EC2 instances.
Why this is correct
The CodeDeploy agent is a prerequisite component that must be installed and actively running on every EC2 instance target. If it is absent, stopped, or unresponsive, the instance will never poll the CodeDeploy service for work, so the deployment will show that instance stuck in the 'Pending' state and ultimately fail from timeout. A key sign: there are no deployment-root directories or log entries under /opt/codedeploy-agent on the instance, meaning no agent process is alive to execute any deployment steps.
- ✗
The IAM instance profile does not have permissions to download from Amazon S3.
Why it's wrong here
While the CodeDeploy agent does need permission via the IAM instance profile to fetch the application revision from S3, a missing or misconfigured policy produces a different, later-stage failure. In this case you would see the agent running and the deployment progress to the 'Download' phase, where it would fail with an error such as 'Cannot download the revision from S3: AccessDenied'. The symptom of instances remaining in 'Pending' indicates the agent itself is not operating, so the IAM issue cannot be the root cause here.
- ✗
The application revision is not a compressed archive.
Why it's wrong here
CodeDeploy does not strictly require the revision to be a compressed archive; a single uncompressed file is also a valid revision format. Even when an archive is used, if the format is unsupported or malformed, CodeDeploy would reject the upload or fail during the download/validation stage with an explicit error like 'Unsupported archive format', which is clearly distinct from an instance that never transitions out of 'Pending'. Since the deployment fails before any instance-side action, this cannot explain the observed symptom of stale, waiting instances.
- ✗
The deployment configuration 'AllAtOnce' is incompatible with Auto Scaling groups.
Why it's wrong here
The predefined deployment configuration 'AllAtOnce' is fully compatible with Auto Scaling groups; it tells CodeDeploy to shift all traffic to the new revision at the same time, which is an accepted strategy. If a deployment configuration were truly incompatible, AWS would reject the request at creation time with a validation error, not silently leave instances stuck during a deployment. Here, the deployment is apparently created and running, so the issue is operational on the instances, not a configuration-level incompatibility.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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Same concept, more angles
1 more way this is tested on DOP-C02
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 company uses AWS CodeDeploy to deploy a web application to an Auto Scaling group of Amazon EC2 instances. The deployment fails with the error 'The overall deployment failed because too many individual instances failed deployment, too few healthy instances are available for deployment, or some instances in your deployment group are experiencing problems.' The application is deployed to the instances using an in-place deployment. The instances are running Amazon Linux 2. What should the DevOps engineer check first?
medium- A.Check the security group rules for the EC2 instances.
- B.Check the application's port availability.
- ✓ C.Verify that the AWS CodeDeploy agent is installed and running on each EC2 instance.
- D.Verify that the IAM instance profile associated with the instances has the correct permissions.
Why C: The error message indicates that individual instances failed deployment, which is most commonly caused by the AWS CodeDeploy agent not running or not being installed on the EC2 instances. For an in-place deployment on Amazon Linux 2, the CodeDeploy agent must be installed and actively running to receive and execute deployment commands from the CodeDeploy service. If the agent is missing or stopped, the instance cannot participate in the deployment, leading to the 'too many individual instances failed' error.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DOP-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DOP-C02 exam.