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 understanding the difference between event-driven triggers versus scheduled invocations and choosing the most operationally efficient solution that balances automation with minimal maintenance. In production, this is about knowing exactly which AWS service natively supports scheduled events without overhead or custom infrastructure. Let’s drill down.
The Certification Drill (Simulated Question) #
Scenario #
DataFlux Solutions is a data analytics startup. They have an AWS Lambda function responsible for generating a daily summary report by analyzing large volumes of data stored in an Amazon S3 bucket. The Lambda must run once every day, exactly at the end of the day, with no manual intervention. The SysOps team needs to implement a scalable, cost-effective, and operationally efficient automation for invoking this Lambda function on a daily schedule.
The Requirement: #
Design the MOST operationally efficient solution to automate invoking a Lambda function to run once daily and process data stored in an S3 bucket.
The Options #
- A) Create an Amazon EventBridge (CloudWatch Events) rule that listens for Amazon S3 object-level events and configures the Lambda function as a target.
- B) Create an Amazon EventBridge (CloudWatch Events) rule with a fixed schedule (cron or rate expression) targeting the Lambda function.
- C) Configure Amazon S3 event notifications to trigger the Lambda function whenever an object is created or modified.
- D) Deploy an Amazon EC2 instance running a cron job that calls the Lambda function API every day.
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Correct Answer #
B
Quick Insight: The SysOps Automation Imperative #
- For SysOps: Scheduled tasks without additional infrastructure reduce operational overhead and eliminate points of failure. EventBridge rules with cron expressions natively provide reliable, serverless scheduling.
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 #
Using an Amazon EventBridge scheduled rule (also previously called CloudWatch Events) to trigger the Lambda function on a daily schedule is the most operationally efficient approach. EventBridge is a fully managed serverless event bus that supports cron or rate expressions, enabling precise, reliable scheduling without needing to maintain servers or additional state.
- It requires no EC2 instance or external infrastructure, eliminating maintenance, patching, and availability concerns.
- Since the function must run exactly once daily at a fixed time, a scheduled invocation is much more straightforward than reacting to S3 object events.
- EventBridge natively integrates with Lambda as a target, simplifying permission setup and monitoring.
- This approach ensures minimal operational overhead—no need for manual cron jobs or polling.
The Trap (Distractor Analysis): #
-
Why not A or C?
These rely on S3 event-driven triggers—invoking the Lambda when objects are created or changed. While useful for near-real-time processing, they do not guarantee a single invocation once a day. S3 event notifications trigger per object event, which might cause multiple invocations or none if no data changed that day. This contradicts the requirement for a daily, scheduled invocation. -
Why not D?
Deploying an EC2 instance just to run a cron job is overkill operationally and financially. This adds unnecessary server management, patches, and scaling complexity when a fully managed serverless solution exists. This is inefficient and violates best practices for automation in the cloud.
The Technical Blueprint #
Relevant AWS CLI command to create a scheduled EventBridge rule invoking Lambda:
# Create EventBridge rule with a daily schedule at 23:59 UTC
aws events put-rule --name "DailyLambdaInvocation" --schedule-expression "cron(59 23 * * ? *)"
# Add Lambda function target to the rule
aws events put-targets --rule "DailyLambdaInvocation" --targets "Id"="1","Arn"="arn:aws:lambda:region:account-id:function:YourLambdaFunction"
# Grant permission for EventBridge to invoke the Lambda function
aws lambda add-permission --function-name YourLambdaFunction --statement-id "EventBridgeInvoke" --action "lambda:InvokeFunction" --principal events.amazonaws.com --source-arn arn:aws:events:region:account-id:rule/DailyLambdaInvocation
The Comparative Analysis #
| Option | Operational Overhead | Automation Level | Impact |
|---|---|---|---|
| A | Low | Event-driven | Triggers on every object event, not once daily |
| B | Very Low | Scheduled (Cron) | Precisely triggers Lambda once daily with no infra |
| C | Low | Event-driven | Same as A - multiple triggers possible |
| D | High | Manual/Server-based | Requires EC2 maintenance and costs |
Real-World Application (Practitioner Insight) #
Exam Rule #
For the exam, always pick EventBridge Scheduled Rules when you see “run Lambda on a schedule” or “run once daily” requirements.
Real World #
In real production environments, many teams still default to EC2-hosted cron jobs out of habit or legacy setups. But adopting EventBridge scheduled rules increases reliability, reduces operational burden, and lowers cost, aligning perfectly with cloud-native best practices.
(CTA) Stop Guessing, Start Mastering #
Disclaimer
This is a study note based on simulated scenarios for the SOA-C02 exam.