iOS Engineer's Experience Taking 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 of server technologies beyond my specialty in mobile app development."
After passing AIF in mid-August, I immediately started studying for CLF while maintaining 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 after the end of September.
Before I knew it, January 2026 had arrived. With the new year, I was determined to complete last year's unfinished business by achieving the CLF certification, so I resumed studying after about a 3-month break.
This article summarizes the information needed for the CLF exam that I gathered while studying. Please note that there is no iOS engineering content in this article.
About the Author
- Mobile app engineer with 16 years of experience
- Holds one AWS certification (AWS Certified AI Practitioner)
- Has never used AWS in a professional capacity
- Has only used Route 53, S3, and CloudFront briefly for personal projects
- Regular Claude user
What is AWS Certified Cloud Practitioner?
AWS Certified Cloud Practitioner is an entry-level certification that validates fundamental knowledge of the AWS Cloud. This 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 are scored, 15 are unscored questions evaluated for future exams) |
| Passing Score | 700 points (out of 1000 points, approximately 70% correct answers) |
| Exam Fee | 15,000 yen |
| Question Format | Multiple choice, multiple select |
| Available Languages | Japanese (other languages available) |
| Testing Method | Test center or at-home exam |
The above information is as of January 2026.
Like with the AIF exam, I chose to take the test at a test center. The at-home exam requires environmental setup and monitoring to prevent cheating, which I found troublesome, making the test center more convenient despite having to go out.
Exam Content (By Domain)
As of January 2026, the exam guideline 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 is an exam that comprehensively tests general knowledge of AWS.
Learning Timeline
After the new year, I was determined to achieve the CLF certification that I had left unfinished last year. However, there was actually a 3-month interruption period, and I ended up intensively studying for about two weeks from mid-January.
Phase 1: Late August to End of September 2025 (Initial Learning Period)
August 20 (Day 1): Start of Learning and Selecting Study Materials
First, to gauge my ability, I tried the official practice question set available on Skill Builder: "Official Practice Question Set: AWS Certified Cloud Practitioner (CLF-C02 - Japanese)" and scored 60% (12/20 questions). I could answer questions on topics I had studied for AIF, but realized I was weak in security and billing domains that weren't covered in AIF.
Like with AIF-C01, other people's exam experiences mentioned passing 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 AIF.
I purchased "最短突破 AWS認定 クラウドプラクティショナー 合格対策テキスト+問題集" (Quick Path to AWS Certified Cloud Practitioner: Exam Prep Text and Questions) to read.
August 21 (Day 2): Trying Udemy Mock Exam After AIF Certification
Riding the momentum from passing AIF, I took CLF mock exam #4 I had purchased on Udemy. The result was a disappointing 64% correct answer rate (42 correct answers). While knowledge from AIF helped in some areas, it became clear that I lacked knowledge about general AWS services and pricing structures.
September 1 to September 27: Continuous Learning
During this period, I had relatively more time and continuously took mock exams, mainly on weekends.
- 9/1 (Sun): Udemy #4 76% (50 correct) - +12% improvement from previous attempt
- 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 thought "I want to take the exam with a bit more confidence" and postponed booking the exam.
Phase 2: October to December 2025 (Learning Interruption Period)
Due to a busy period at work and continued care for my degu, my studies came to a complete halt. The goal of obtaining CLF remained in the back of my mind, but I didn't have the capacity to work on it.
Phase 3: January 10 to January 25, 2026 (Final Push Period)
At the end of December, my degu's surgery was successful and the urgency of nursing care decreased, so I finally had an environment where I could focus on studying. I renewed my determination to "obtain CLF this year."
January 10 (Fri): Resuming Studies After About 3 Months
First, I wanted to assess my current skill level.
I retook the AWS official practice questions (20 questions) and scored 75% (15 correct answers).
Next, I took a ping-t random test (65 questions) that I had newly registered for and scored 78% (51 correct answers).
In the evening, I took Udemy mock exam #4 again and scored 75% (49 correct answers). After a 3-month break, my score had dropped by 8% from 83% at the end of September. I keenly felt that "continuous learning is indeed important."
At this point, I determined that "two weeks should be enough time," and scheduled the exam for January 25 (Sun).
January 11-12: Identifying Weaknesses
January 11 (Sat), I took Udemy mock exam #1 and scored 78% (51 correct answers). Slightly improved from the previous day, but still unstable.
On January 12 (Sun), I took two exams. In the morning, I scored 70% (46 correct answers) on a ping-t test, which was a significant drop that made me anxious. However, in the afternoon, when I retook the same test with review, I recovered to 80% (52 correct answers). This gave me confidence that "scores can improve in a short period with review."
January 13-15: Interruption (Work Commitments)
During this period, I couldn't secure study time due to work commitments.
January 16-18: Breaking Through the 90% Barrier
On January 16 (Thu), I took Udemy mock exam #3 after a while and achieved a 92% correct answer rate (60 correct answers). This was the first time I exceeded 90%. I felt that my reviews were finally paying off.
On January 17 (Fri), I scored 67% (44 correct answers) on a ping-t random test in the morning, dropping again, but in the afternoon, I recorded 93% (61 correct answers) on Udemy mock exam #1. I noticed a 26% difference between ping-t and Udemy.
Upon investigation, I found that ping-t covers a broader range of topics, including minor services that rarely appear in the actual exam, while Udemy has a difficulty level and question trend closer to the actual exam.
On January 18 (Sat), I scored 89% (58 correct answers) on Udemy mock exam #2. I was now consistently scoring around 90% on Udemy.
January 22-23: Final Adjustments
On January 22 (Wed), I scored 69% (45 correct answers) on a ping-t random test. I continued to struggle 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 answers) score on Udemy mock exam #1 in the morning. In the afternoon, I recovered to 78% (51 correct answers) on a ping-t random test, up +9% from the previous 69%. This confirmed 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 started. I presented my ID (driver's license), stored my belongings in a locker, and received a whiteboard and marker. Earphones were provided, but since they would interfere with my glasses, I requested disposable earplugs instead.
However, even with earplugs, I could hear another test-taker groaning, which made it difficult to concentrate during the first half. When that test-taker left with about 30 minutes remaining, I was able to calmly review my answers.
I'll omit the details of the exam content, but I felt confident. Even though some services and features I hadn't studied came up, I was able to answer using the process of elimination or context.
I left after about 70 minutes of the 90-minute exam time.
At 21:18 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
At 6:27 the next morning, I found the official pass notification in my AWS T&C account. When I logged into the portal, my score was 856 points, and I was relieved to have passed.
Reflection
I reflected on my CLF exam experience from several perspectives.
About Study Time
I was able to pass with about 22.5 hours of study. The breakdown is as follows:
| Study Content | Hours |
|---|---|
| Reading preparation textbook | 6h |
| Udemy mock exams (Aug-Sept) | 7h |
| AWS official practice questions (Jan) | 0.5h |
| ping-t mock exams (Jan) | 5h |
| Udemy mock exams (Jan) | 4h |
| Total | 22.5h |
Compared to the AIF exam (11 hours), this took about twice as much study time. This is because while AIF was specialized in AI/ML, CLF required comprehensive learning about AWS in general.
The 3-Month Interruption Was Painful
My biggest mistake was postponing the exam despite reaching 83% by the end of September because I thought "I want to take the exam with a bit more confidence."
When I resumed after 3 months, my score had decreased to 75%, a drop of 8 percentage points. As a result, I had to cram again for two weeks, leaving me with less mental and time flexibility.
The Strategy of Identifying and Eliminating Weaknesses Worked
During this study, I thoroughly analyzed the questions I got wrong and identified weak areas. This made it clear "what I needed to memorize."
Specifically, after taking mock exams on Udemy and ping-t, I input the questions I got wrong into AI and had it create summaries of my weak areas. By having it focus on explaining my weak areas and skipping areas I was good at, I could study efficiently.
This approach may have contributed to my scores quickly exceeding 90%, after struggling to improve last year.
What I Gained from Taking the Exam
Through this exam, I gained a systematic understanding of the overall AWS cloud. While the AIF exam was specialized in AI/ML services, CLF allowed me to comprehensively learn about the foundational knowledge of AWS, including computing, storage, networking, security, and billing.
In particular, concepts such as 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 have obtained 2 AWS certifications (AIF, CLF). Next, I'll take a bit of rest, then consider challenging more specialized Associate-level certifications like "AWS Certified Solutions Architect - Associate" or "AWS Certified Developer - Associate" that could be useful in practical work.
Appendix: Important AWS Services for CLF-C02
The following table lists the main AWS services that appear on the CLF-C02 exam, extracted from the exam guidelines.
| Category | Service Name | Description |
|---|---|---|
| Analytics | Amazon Athena | Interactive queries for data in S3 |
| Analytics | Amazon EMR | Big data processing (Hadoop/Spark, etc.) |
| Analytics | AWS Glue | ETL service |
| Analytics | Amazon Kinesis | Streaming data processing |
| Analytics | Amazon OpenSearch Service | Search and log analysis 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 workflows |
| Business Apps | Amazon Connect | Cloud contact center |
| Business Apps | Amazon SES | Email sending service |
| Cloud Financial Management | AWS Budgets | Budget management, setting 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 estimates |
| Compute | Amazon EC2 | Virtual servers |
| Compute | AWS Lambda | Serverless functions |
| Compute | AWS Elastic Beanstalk | PaaS application environment, allowing developers to 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 DB |
| Database | Amazon Aurora | High-performance RDB (MySQL/Postgres compatible) |
| Database | Amazon DynamoDB | NoSQL database, specializing in ultra-fast, simple access with sub-millisecond latency. Key-value type |
| Database | Amazon DocumentDB | NoSQL database, good for migrations from MongoDB and complex queries. 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 | Amazon AppStream 2.0 | Virtual app delivery |
| End User | Amazon WorkSpaces | Virtual desktop |
| End User | 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 | Chatbot |
| 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 | Consolidated account 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 recommendations |
| 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 assessment |
| Management/Governance | AWS Health Dashboard | Service health checking |
| Networking/Content Delivery | Amazon VPC | Virtual network |
| Networking/Content Delivery | Amazon Route 53 | DNS |
| Networking/Content Delivery | Amazon CloudFront | CDN |
| Networking/Content Delivery | AWS Direct Connect | Private connection between on-premises and AWS (dedicated line) |
| Networking/Content Delivery | AWS Transit Gateway | Central hub connecting multiple VPCs |
| Networking/Content Delivery | AWS VPN | VPN connection |
| Networking/Content Delivery | AWS PrivateLink | Private VPC-to-VPC connection |
| Networking/Content Delivery | AWS Global Accelerator | Global optimal routing |
| Networking/Content 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 that issues temporary security credentials |
| Security | AWS KMS | Encryption key management |
| Security | AWS Shield | Protects against DDoS |
| Security | AWS Web Application Firewall (WAF) | Firewall that protects against common web attacks such as SQL injection |
| Security | AWS Firewall Manager | Integrated FW policy management |
| Security | AWS Artifact | Compliance trail, download reports |
| Security | AWS Security Hub | Integrated security 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 auditing |
| 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 to AWS using a dedicated private connection
- AWS Site-to-Site VPN: Connect on-premises to AWS servers using encrypted internet connections
How to Remember Easily Confused Migration Services
The CLF exam features many questions about migration. I summarized migration services as follows to avoid forgetting them:
- AWS Application Discovery Service: Conduct preliminary migration surveys
- AWS Application Migration Service (AWS MGN): Migrate entire servers
- Example: Migrating an on-premises server entirely to EC2
- AWS Database Migration Service (AWS DMS): Database migration
- Example: Can migrate between same or different types of databases
- AWS Migration Hub: Migration Hub itself doesn't perform migration. It monitors and manages other migration services
AWS Pricing Models to Understand Well
Since CLF-C02 includes 12% of questions about pricing, the following knowledge is important. Make sure to understand these well:
- On-Demand Instances: Pay only for what you use
- Reserved Instances: Discounts for 1-3 year reservations
- Savings Plans: Flexible discounts with 1-3 year commitments
- Spot Instances: Use excess capacity at low prices
