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Limani Ndou
Limani Ndou

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🚀 How I Built a Serverless Expense Tracker Using AWS Lambda and Amazon S3 - No Server Required


🚀I have built a fully serverless expense tracking pipeline on AWS no servers, no manual work, just pure cloud automation.

The problem: combining monthly expense CSVs every year is tedious and error-prone. So I automated the entire process.

🪣 Amazon S3 (Simple Storage Service)
Amazon S3 is a cloud-based object storage service that stores and retrieves any amount of data from anywhere in the world. It can also watch for new files and automatically notify other AWS services when something is uploaded.
💡 Think of it as a smart cloud hard drive the moment a CSV lands in S3, it wakes up Lambda automatically.

⚡ AWS Lambda
AWS Lambda is a serverless compute service that runs your code in response to events, without provisioning or managing any servers. You only pay for the milliseconds your code actually runs.
💡 Think of it as a worker who sleeps until you need them triggered, runs the task, goes back to sleep. No server running 24/7, no idle costs.

🔐 AWS IAM (Identity & Access Management)
AWS IAM is a service that controls access to AWS resources by defining who is authenticated and what actions they are authorised to perform.
💡 Think of it as the security guard of AWS without IAM, Lambda would not be allowed to touch a single file in S3.

📊 Amazon CloudWatch
Amazon CloudWatch is a monitoring and observability service that collects logs, metrics, and events from AWS services in real time.
💡 Think of it as the CCTV of your cloud application every log line, every error, every execution time recorded automatically.

⚙️ How The Pipeline Works:

  1. Upload monthly CSV to S3
  2. S3 fires an event → Lambda wakes up
  3. Lambda reads the new file + existing master
  4. Merges, sorts by date, removes duplicates
  5. Recalculates category totals in South African Rand
  6. Saves updated master file back to S3 instantly

📈 Real Results — 3 Months of SA Expense Data:
• ✅ 50 transactions merged automatically
• ✅ 0 manual steps required
• ✅ Categories: Groceries, Fuel, Utilities, Health & more
• 💰 Grand Total (YTD 2026): R41,859.97

🔗 Full source code, architecture diagram & sample data if you want to try:
👉 https://lnkd.in/dQNytjKD

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