The Jeff’s Note (Contextual Hook) #
Jeff’s Note #
Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Site Reliability Engineer (SRE).
For SOA-C02 candidates, the confusion often lies in cross-region resource dependencies and AMI availability. In production, this is about knowing exactly how AWS regional isolation impacts resource identifiers like AMI IDs and the behavior of CloudFormation in multi-region deployments. Let’s drill down.
The Certification Drill (Simulated Question) #
Scenario #
The IT operations team at TechBridge Solutions has automated EC2 instance deployment using AWS CloudFormation templates to ensure consistent infrastructure across all business units. The team successfully provisioned an EC2 instance in the us-east-1 region but when running the same CloudFormation template in us-west-2, the stack creation fails. They need to identify the root cause quickly to restore their multi-region automation.
The Requirement: #
Identify the most probable technical reason why the CloudFormation template failed when deploying the EC2 instance to the us-west-2 region.
The Options #
- A) Resource tags declared in the CloudFormation template include region-specific values tied to the us-east-1 region.
- B) The Amazon Machine Image (AMI) ID referenced in the template does not exist in the us-west-2 region.
- C) The cfn-init helper script failed to execute during instance initialization in the us-west-2 region.
- D) The IAM user presumed by the template was not created or available in the us-west-2 region.
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Correct Answer #
B
Quick Insight: The SysOps Operational Imperative #
The key operational challenge here is the global uniqueness and regional scope of AMI IDs. An AMI ID valid in us-east-1 will almost always be invalid and unavailable in us-west-2 unless explicitly copied there. This causes stack creation to fail immediately during resource provisioning.
Content Locked: The Expert Analysis #
You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?
The Expert’s Analysis #
Correct Answer #
Option B
The Winning Logic #
CloudFormation stack creation fails because the AMI ID specified is region-specific and must be valid in the region where the stack is deployed. AWS AMI IDs are not global; each region maintains its own set of AMIs. Unless the AMI is explicitly copied to us-west-2 (using aws ec2 copy-image or a similar method), referencing an AMI from us-east-1 in a us-west-2 stack will cause the launch to fail with an “InvalidAMIID.NotFound” error event. This is a common pitfall in multi-region deployments.
The Trap (Distractor Analysis): #
-
Why not A?
Resource tags can have region-specific values, but they do not prevent resource creation or cause stack failure. Tags are metadata and usually do not affect provisioning success. -
Why not C?
Failure ofcfn-initscripts happens post-instance launch and initialization, not during the EC2 instance creation step. The question states the stack failed to create the EC2 instance itself. -
Why not D?
IAM users are global and IAM resources are not tied to AWS Regions. IAM existence or permissions errors manifest differently during stack creation and would not be region-specific in this manner.
The Technical Blueprint #
# To copy an AMI from us-east-1 to us-west-2 region before deployment:
aws ec2 copy-image \
--source-image-id ami-1234567890abcdef0 \
--source-region us-east-1 \
--region us-west-2 \
--name "CopiedAMI"
Running the above command creates a new AMI in us-west-2, enabling CloudFormation templates referencing this AMI to succeed in that region.
The Comparative Analysis #
| Option | Operational Overhead | Automation Level | Impact on Deployment |
|---|---|---|---|
| A | Low | None | Does not block provisioning |
| B | High (requires AMI copying) | Manual or scripted copy | Prevents EC2 creation |
| C | Medium | Debugging cfn-init setup | Affects instance config, not creation |
| D | Low | None | IAM global, not region-bound |
Real-World Application (Practitioner Insight) #
Exam Rule #
For EC2 cross-region deployments, always verify the AMI ID exists in the target region or automate AMI replication.
Real World #
In actual operations, teams implement pipelines or Lambda functions to automatically copy or create region-specific AMIs before deployment, maintaining infrastructure as code consistency without manual intervention.
(CTA) Stop Guessing, Start Mastering #
Disclaimer
This is a study note based on simulated scenarios for the AWS SOA-C02 exam.