iOS Engineer Takes the AWS Certified Cloud Practitioner (CLF-C02) - CLF Success Story
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In August 2025, when I obtained AWS Certified AI Practitioner (AIF), I wrote that "next, I want to take the AWS Certified Cloud Practitioner (CLF) exam and deepen my knowledge about server technologies beyond my specialty in mobile app development."
After passing the AIF in mid-August, I immediately began studying for the CLF, riding on that momentum. However, due to a busy period at work and having to care for my pet degu who developed malocclusion requiring nursing care, my studies were interrupted at the end of September.
Before I knew it, it was January 2026. With the new year, I was determined to complete last year's homework by achieving the CLF certification, so I resumed studying after a roughly three-month break.
This article summarizes the information needed for the CLF exam based on my study experience. Please note that there is no iOS engineer-specific content here.
About the Author
- Mobile app engineer with 16 years of experience
- Holds 1 AWS certification (AWS Certified AI Practitioner)
- No experience using AWS professionally
- Only light personal experience with Route 53, S3, and CloudFront
- Regular Claude user
What is AWS Certified Cloud Practitioner?
AWS Certified Cloud Practitioner is an entry-level certification that demonstrates foundational knowledge of the AWS Cloud. The exam is referred to as "CLF" from its exam code "CLF-C02."
Exam Overview
| Item | Details |
|---|---|
| Exam Duration | 90 minutes |
| Number of Questions | 65 questions (50 scored, 15 unscored questions evaluated for future exams) |
| Passing Score | 700 points (out of 1000, approximately 70% correct answers) |
| Exam Fee | 15,000 yen |
| Exam Format | Multiple choice, multiple selection questions |
| Available Languages | Japanese (and others) |
| Exam Method | Test center or home proctored exam |
The above information is current as of January 2026.
Like when I took the AIF exam, I chose to take the test at a test center. While home exams require environmental preparation and uncomfortable monitoring to prevent cheating, taking it at a test center is more convenient despite having to go out.
Exam Content (by Domain)
According to the exam guidelines as of January 2026, the exam covers the following domains:
| Domain | Percentage | Main Content |
|---|---|---|
| Cloud Concepts | 24% | Cloud computing value proposition, AWS Cloud economics, cloud architecture design principles |
| Security and Compliance | 30% | Shared responsibility model, security and compliance concepts, access management features, security support resources |
| Cloud Technology and Services | 34% | Understanding AWS services, deployment and operations, global infrastructure |
| Billing, Pricing, and Support | 12% | Pricing models, billing and cost management, support resources |
Compared to AIF (AI/ML specialized), CLF covers foundational knowledge of AWS in general. During AIF, my experience with CoreML and CreateML was helpful, but since I don't work with AWS professionally, I studied with the feeling of "this would be easy if I used it at work..."
Learning Timeline
Upon entering the new year, I was determined to achieve the CLF certification that I had left unfinished from the previous year. However, there was actually a three-month interruption period, and I ultimately ended up cramming in about two weeks from mid-January.
Phase 1: Late August to Late September 2025 (Initial Learning Period)
August 20 (Day 1): Learning Start and Material Selection
To check my current ability, I first tried the official Skill Builder's "Official Practice Question Set: AWS Certified Cloud Practitioner (CLF-C02 - Japanese)" and scored 60% (12/20 questions). I could correctly answer questions from topics I had studied for AIF, but realized my weakness in security and billing domains that weren't covered.
According to others' exam experiences for CLF-C02, like AIF-C01, it was possible to pass with just practice questions without buying a textbook. However, since I don't regularly use AWS, I decided to start with systematic learning as I did for the AIF exam.
I purchased "Shortest Path AWS Certified Cloud Practitioner Preparation Text + Question Collection" and began studying.
August 21 (Day 2): Taking Udemy Practice Test Right After AIF Pass
Riding on the momentum of passing AIF, I took Udemy practice test #4 that I had purchased. The result was a disappointing 64% accuracy (42 correct answers). While knowledge from AIF was helpful in some areas, it became clear that my knowledge of general AWS services and pricing structures was insufficient.
September 1-27: Continuous Learning
During this period, I had relatively more time and continuously took practice tests, especially on weekends.
- 9/1 (Sun): Udemy #4 76% (50 correct) - +12% improvement from last time
- 9/2 (Mon): Udemy #4 84% (55 correct) - First time exceeding 80%
- 9/6 (Fri): Udemy #3 69% (45 correct), Udemy #4 83% (54 correct), Udemy #3 87% (57 correct)
- 9/7 (Sat): Udemy #1 75% (49 correct)
- 9/8 (Sun): Udemy #2 75% (49 correct)
- 9/27 (Fri): Udemy #1 83% (54 correct)
At this point, I had reached the low 80% range, but I decided to postpone making an exam reservation, thinking "I want to take the exam with a bit more confidence."
Phase 2: October-December 2025 (Study Interruption Period)
Due to a busy period at work and continuing care for my degu, my studies completely stopped. The goal of obtaining CLF was still in the back of my mind, but I didn't have the capacity to work on it.
Phase 3: January 10-25, 2026 (Final Push Period)
At the end of December, my degu's surgery was successful and the urgency of care decreased, allowing me to finally focus on studying. I renewed my determination to "obtain CLF this year."
January 10 (Fri): Resuming Study After About 3 Months
I decided to first assess my current ability.
Taking the AWS official practice questions (20 questions) again, I scored 75% (15 correct answers).
Next, I took a ping-t random test (65 questions) which I had newly registered for, scoring 78% (51 correct answers).
In the evening, I took the Udemy practice test #4 after a long break and scored 75% (49 correct answers). After the 3-month break, I had dropped 8% from the 83% at the end of September. This made me keenly aware of the importance of continuous learning.
At this point, I judged that "two weeks should be enough" and made a reservation for January 25 (Sun).
January 11-12: Identifying Weaknesses
January 11 (Sat), I took Udemy practice test #1 and scored 78% (51 correct answers). Slightly improved from the previous day, but still unstable.
On January 12 (Sun), I took tests twice. In the morning, I scored 70% (46 correct) on a ping-t test, which made me anxious. However, in the afternoon, I retook the same test with review and improved to 80% (52 correct). This gave me confidence that "scores can improve in a short time with review."
January 13-15: Break (Work Circumstances)
During this period, I couldn't secure study time due to work commitments.
January 16-18: Breaking Through the 90% Wall
On January 16 (Thu), I took Udemy practice test #3 after a while and achieved 92% accuracy (60 correct answers). I exceeded 90% for the first time. I felt that my reviews were finally paying off.
On January 17 (Fri), I scored 67% (44 correct) on a ping-t random test in the morning, but in the afternoon scored 93% (61 correct) on Udemy practice test #1. I noticed a 26% difference between ping-t and Udemy.
Upon investigation, I discovered that ping-t covers a broader range of topics, including minor services that rarely appear in the actual exam, while Udemy's difficulty and question patterns are closer to the actual exam.
On January 18 (Sat), I scored 89% (58 correct) on Udemy practice test #2. I was now consistently scoring around 90% on Udemy.
January 22-23: Final Adjustments
On January 22 (Wed), I scored 69% (45 correct) on a ping-t random test. I was still struggling with ping-t but decided to accept that "the actual exam should be closer to Udemy."
On January 23 (Thu), the day before the exam, I replicated a 93% (61 correct) score on Udemy practice test #1 in the morning. In the afternoon, I improved to 78% (51 correct) on a ping-t random test, a +9% increase from the previous 69%, confirming that my skills were definitely improving.
At this point, I analyzed the questions I got wrong and identified weak areas. I created notes to review on the morning of the exam day.
January 25 (Sun): Exam Day
On the train to the test center, I made final reviews of my weak areas.
I arrived at the test center 30 minutes before the exam start. I presented my ID (driver's license), stored my belongings in a locker, and received a whiteboard and marker. There were earphones available, but I got disposable earplugs as the earphones interfered with my glasses.
However, even with earplugs, I could hear other test takers' groans, which made it difficult to concentrate during the first half. When that test taker left with 30 minutes remaining, I was able to calmly review my answers.
While I'll omit the details of the exam content, I felt confident. Even though services and features I hadn't studied appeared in questions, I was able to answer using the process of elimination or contextual inference.
I left after about 70 minutes of the 90-minute exam time.
At 9:18 PM that day, I received an email from Credly saying "Congratulations! You've earned a badge from Amazon Web Services Training and Certification!"
January 26 (Mon): Pass Notification
The next day at 6:27 AM, an official pass notification had arrived in my AWS T&C account. When I logged into the portal site, my score was 856 points, and I was relieved to have passed successfully.
Reflection
I reflected on my CLF exam experience from several perspectives.
About Study Time
I was able to pass with approximately 22.5 hours of study. The breakdown is as follows:
| Study Content | Time |
|---|---|
| Reading preparation textbook | 6h |
| Udemy practice tests (August-September) | 7h |
| AWS official practice questions (January) | 0.5h |
| ping-t practice tests (January) | 5h |
| Udemy practice tests (January) | 4h |
| Total | 22.5h |
Compared to the AIF exam (11 hours), this took about twice as much study time. This is because AIF was AI/ML specialized, whereas CLF required comprehensive learning about AWS in general.
The 3-Month Interruption Hurt
My biggest mistake was postponing the exam when I had already reached 83% at the end of September, thinking "I want to take the exam with a bit more confidence."
When I resumed after 3 months, my score had decreased to 75%, dropping 8 percentage points. As a result, I had to cram again for two weeks, which left me with less mental and time margin.
The Strategy of Identifying and Addressing Weaknesses Worked
In this study approach, I thoroughly analyzed the questions I got wrong and identified weak areas. This made it clear "what I needed to memorize."
Specifically, after taking Udemy and Ping-t practice tests, I input the questions I got wrong into an AI and had it create summaries of my weak areas. By having it focus explanations on weak areas rather than strong ones, I was able to study efficiently.
This approach seemed to work well, as my score, which had been stagnating last year, suddenly exceeded 90%.
What I Gained from the Exam
Through this exam, I gained a systematic understanding of the overall AWS cloud. While the AIF exam focused on AI/ML services, CLF allowed me to comprehensively learn about computing, storage, networking, security, billing, and other foundational knowledge of AWS.
In particular, concepts like the shared responsibility model, Well-Architected Framework, and cost optimization are essential knowledge for utilizing AWS in the future, and I'm glad I learned them.
Next Steps
With this exam, I've obtained 2 AWS certifications (AIF, CLF). Next, I'd like to take a break and then challenge more specialized Associate-level certifications that would be useful in practical work... such as "AWS Certified Solutions Architect - Associate" or "AWS Certified Developer - Associate."
I hope this is helpful for those considering taking the CLF exam, especially developers who don't regularly work with AWS.
Appendix: Important AWS Services for CLF-C02
The following table lists the main AWS services covered in the CLF-C02 exam, extracted from the exam guidelines.
| Category | Service Name | Description |
|---|---|---|
| Analytics | Amazon Athena | Interactive queries on S3 data |
| Analytics | Amazon EMR | Big data processing (Hadoop/Spark etc.) |
| Analytics | AWS Glue | Data ETL service |
| Analytics | Amazon Kinesis | Streaming data processing |
| Analytics | Amazon OpenSearch Service | Search and log analytics service |
| Analytics | Amazon QuickSight | BI/visualization service |
| Analytics | Amazon Redshift | Data warehouse |
| App Integration | Amazon EventBridge | Event bus |
| App Integration | Amazon SNS | Push notifications/Pub-Sub |
| App Integration | Amazon SQS | Message queue |
| App Integration | AWS Step Functions | Serverless workflow |
| Business Apps | Amazon Connect | Cloud contact center |
| Business Apps | Amazon SES | Email sending service |
| Cloud Financial Management | AWS Budgets | Budget management. Set budgets and alerts |
| Cloud Financial Management | AWS Cost Explorer | Cost analysis and visualization |
| Cloud Financial Management | AWS Cost and Usage Report | Detailed usage reports |
| Cloud Financial Management | AWS Marketplace | Purchase third-party products |
| Cloud Financial Management | AWS Pricing Calculator | Monthly cost estimation |
| Compute | Amazon EC2 | Virtual servers |
| Compute | AWS Lambda | Serverless functions |
| Compute | AWS Elastic Beanstalk | PaaS application runtime. Developers can deploy without worrying about resources |
| Compute | Amazon Lightsail | Simple VPS service |
| Compute | AWS Outposts | AWS environment for on-premises |
| Compute | AWS Batch | Batch processing |
| Containers | Amazon ECR | Container image registry |
| Containers | Amazon ECS | Container orchestration |
| Containers | Amazon EKS | Managed Kubernetes |
| Database | Amazon RDS | Relational database |
| Database | Amazon Aurora | High-performance RDB (MySQL/Postgres compatible) |
| Database | Amazon DynamoDB | NoSQL database. Excels at super-fast, simple access with sub-millisecond latency. Key-value type |
| Database | Amazon DocumentDB | NoSQL database. Good for complex queries and MongoDB migration. Document type |
| Database | Amazon ElastiCache | In-memory cache |
| Database | Amazon Neptune | Graph database |
| Developer Tools | AWS CLI | Command-line management |
| Developer Tools | AWS CodeBuild | Build service |
| Developer Tools | AWS CodePipeline | CI/CD service |
| Developer Tools | AWS X-Ray | Distributed tracing |
| End User Computing | Amazon AppStream 2.0 | Virtual app delivery |
| End User Computing | Amazon WorkSpaces | Virtual desktop |
| End User Computing | Amazon WorkSpaces Secure Browser | Secure browser environment |
| Frontend/Mobile | AWS Amplify | Frontend development platform |
| Frontend/Mobile | AWS AppSync | GraphQL API service |
| IoT | AWS IoT Core | IoT device connection management |
| Machine Learning | Amazon SageMaker AI | ML model building/training/inference |
| Machine Learning | Amazon Comprehend | Natural language processing |
| Machine Learning | Amazon Kendra | Enterprise search |
| Machine Learning | Amazon Lex | Chatbots |
| Machine Learning | Amazon Polly | Speech synthesis |
| Machine Learning | Amazon Rekognition | Image recognition |
| Machine Learning | Amazon Textract | OCR (document text extraction) |
| Machine Learning | Amazon Transcribe | Speech recognition |
| Machine Learning | Amazon Translate | Machine translation |
| Machine Learning | Amazon Q | AWS generative AI service |
| Management/Governance | AWS Organizations | Account unified management |
| Management/Governance | AWS Control Tower | Multiple account governance |
| Management/Governance | AWS Config | Configuration change tracking |
| Management/Governance | AWS CloudFormation | IaC construction |
| Management/Governance | AWS CloudTrail | API call recording |
| Management/Governance | Amazon CloudWatch | Monitoring service |
| Management/Governance | AWS Trusted Advisor | Recommended best practices |
| Management/Governance | AWS Compute Optimizer | Resource optimization suggestions |
| Management/Governance | AWS License Manager | License management |
| Management/Governance | AWS Service Catalog | Service catalog management |
| Management/Governance | AWS Systems Manager | Operations management |
| Management/Governance | AWS Well-Architected Tool | Architecture evaluation |
| Management/Governance | AWS Health Dashboard | Service health check |
| Network/Delivery | Amazon VPC | Virtual network |
| Network/Delivery | Amazon Route 53 | DNS |
| Network/Delivery | Amazon CloudFront | CDN |
| Network/Delivery | AWS Direct Connect | Private connection between on-premises and AWS (dedicated line) |
| Network/Delivery | AWS Transit Gateway | Central hub connecting multiple VPCs |
| Network/Delivery | AWS VPN | VPN connection |
| Network/Delivery | AWS PrivateLink | Private connection between VPCs |
| Network/Delivery | AWS Global Accelerator | Global optimal routing |
| Network/Delivery | Amazon API Gateway | API publishing service |
| Security | AWS IAM | Identity and access management |
| Security | AWS IAM Identity Center | Single sign-on |
| Security | AWS Security Token Service (AWS STS) | Service to issue temporary security credentials |
| Security | AWS KMS | Encryption key management |
| Security | AWS Shield | Protects from DDoS |
| Security | AWS Web Application Firewall (WAF) | Firewall. Protects from common web attacks like SQL injection |
| Security | AWS Firewall Manager | Unified FW policy management |
| Security | AWS Artifact | Compliance trail. Download reports |
| Security | AWS Security Hub | Security unified management |
| Security | Amazon GuardDuty | Threat detection |
| Security | Amazon Inspector | Vulnerability management |
| Security | Amazon Detective | Security investigation |
| Security | Amazon Macie | Data discovery and classification |
| Security | AWS Audit Manager | Compliance audit |
| Security | AWS Certificate Manager | SSL/TLS certificate management |
| Security | AWS CloudHSM | Dedicated HSM encryption |
| Security | AWS Secrets Manager | Secret management |
| Security | AWS Directory Service | Active Directory compatible |
| Security | AWS RAM | Resource sharing |
| Storage | Amazon S3 | Object storage |
| Storage | Amazon S3 Glacier | Low-cost archive |
| Storage | Amazon EBS | Block storage |
| Storage | Amazon EFS | File storage |
| Storage | Amazon FSx | Windows/high-performance FS |
| Storage | AWS Storage Gateway | Hybrid cloud storage |
| Storage | AWS Backup | Backup management |
| Storage | AWS Elastic Disaster Recovery | Disaster recovery |
How to Remember Easily Confused Connect Services
- Amazon Connect: Call center
- AWS Direct Connect: Connect on-premises and AWS with a dedicated private connection
- AWS Site-to-Site VPN: Connect on-premises and AWS servers using encrypted internet connection
How to Remember Easily Confused Migration Services
Many questions about migration appear on the CLF exam. I summarized migration services as follows to not forget them:
- AWS Application Discovery Service: Conducts pre-migration investigation
- AWS Application Migration Service (AWS MGN): Migration of entire servers
- Example: Migrating an on-premises server to EC2
- AWS Database Migration Service (AWS DMS): Database migration
- Example: Enables migration between similar or different database types
- AWS Migration Hub: Migration Hub itself doesn't perform migration work. It monitors and manages other migration services.
Important AWS Pricing Models to Understand
Since 12% of CLF-C02 questions are about pricing, the following knowledge is important to understand thoroughly:
- On-Demand Instances: Pay only for what you use
- Reserved Instances: Discount for 1-3 year reservation
- Savings Plans: Flexible discount with 1-3 year commitment
- Spot Instances: Use excess capacity at low cost
