In today’s tech interviews, system design has become a crucial deciding factor, especially in fintech companies like Lendbuzz that emphasize high concurrency, real-time data processing, API integrations, and security. For many engineers, system design is not their strongest skill, often leading to logical confusion, unclear articulation, or impractical solutions that cost them the opportunity.

If you have similar concerns, don't worry—CSOAHELP’s remote interview assistance ensures that even if you lack system design experience, you can deliver structured answers, articulate ideas clearly, and ultimately secure the offer. This article walks through a real Lendbuzz interview experience, showing how CSOAHELP helped a candidate navigate the challenge.

The interviewer got straight to the point, presenting the following question:

System Design Question: Bank Transaction Analysis System
Problem Statement:
You are designing a system that pulls user bank transactions from external financial institutions and analyzes them based on predefined rules. The system should allow users to connect their bank accounts, fetch transaction data, and apply custom rules for categorization, fraud detection, and spending analysis.

At first glance, this question seems to focus on building a bank transaction data analysis system, but in reality, it tests multiple aspects:

• External API integration (How efficiently can you retrieve data from third-party financial institutions?)
• Data storage & processing (How do you store massive transaction data? How do you optimize queries?)
• Rule engine & fraud analysis (How do you define scalable, customizable rules? How do you perform real-time detection?)
• System scalability (How do you handle high user concurrency? How do you optimize system performance?)

For a candidate without extensive experience, structuring a well-reasoned response could be difficult. However, with CSOAHELP’s remote interview assistance, the candidate remained composed and provided clear, well-organized answers at every stage.

With CSOAHELP’s full-text guidance, the candidate avoided the common pitfall of diving into details too quickly and instead began with a high-level architecture overview:

"To design this system, we can break it down into four main components: Bank Account Integration, Transaction Storage, Rule Engine, and Notification System. Each component has a distinct responsibility, ensuring scalability and maintainability.”

"The Bank Account Integration module connects and retrieves transaction data from banks."
"Transaction Storage keeps a record of all user transactions."
"The Rule Engine applies user-defined rules for categorization and fraud detection."
"The Notification System alerts users when a transaction violates a rule."

The interviewer acknowledged this well-structured approach and asked, “How would you design the bank account integration?”

With CSOAHELP’s remote assistance, the candidate immediately received a full-text response and simply read it out:

"For bank account integration, we need to interact with third-party financial data providers such as Plaid or Yodlee. These APIs provide OAuth authentication and webhook callbacks, allowing us to securely fetch user transactions. When a user links a bank account, we trigger an initial full data fetch to retrieve the past six months of transactions. Subsequently, a scheduled job (Cron Job or AWS Lambda + EventBridge) performs incremental updates to avoid redundant data fetching."

"To optimize API requests, we use Kafka or RabbitMQ as a message queue to handle asynchronous data processing and improve throughput."

The interviewer was pleased with the response and asked, “How would you handle data storage?”

CSOAHELP quickly provided a detailed text response, allowing the candidate to answer fluently:

"Bank transaction data is characterized by high read/write concurrency, and query patterns mainly involve searching by user and time range. Therefore, we can use a combination of PostgreSQL (structured data storage with JSONB for transaction details) and Elasticsearch (full-text search and fuzzy matching capabilities)."

"Here’s a basic schema for our transactions table:"

CREATE TABLE transactions (
    id SERIAL PRIMARY KEY,
    user_id INT NOT NULL,
    bank_account_id INT NOT NULL,
    amount DECIMAL(10,2) NOT NULL,
    currency VARCHAR(3),
    transaction_type VARCHAR(50),
    transaction_time TIMESTAMP,
    metadata JSONB
);

"PostgreSQL handles structured queries, while Elasticsearch enables searching for transactions containing specific keywords like ‘Amazon’."

The interviewer followed up, “If the user base grows, won’t the database become a bottleneck?”

CSOAHELP immediately provided a database scaling strategy, which the candidate repeated:

"To handle scalability, we can implement database sharding, partitioning data horizontally based on user_id. Additionally, caching frequently accessed data in Redis reduces database load. To support real-time data processing, we can leverage Change Data Capture (CDC) with Kafka, ensuring updates are propagated efficiently."

The interviewer then asked, “How would you allow users to define custom rules?”

With CSOAHELP’s full-text response, the candidate seamlessly answered:

"We can build a rule-based engine that enables users to define conditions such as ‘If a transaction amount is greater than $2000 and categorized as an international transfer, mark it as high-risk.’"

"Rules would be stored in NoSQL (MongoDB), and executed using a stream-processing framework like Flink or Spark Streaming to evaluate transactions in real-time."

"When a transaction matches a rule, it triggers a Kafka event, sending an alert through the notification system."

During this interview, the candidate initially had limited system design experience, but thanks to CSOAHELP’s remote interview assistance, he consistently delivered comprehensive, professional, and well-structured answers. Instead of struggling with uncertainty or hesitation, he provided confident, industry-standard responses that left a strong impression on the interviewer, ultimately securing the offer.

If you worry about your system design skills or tend to get nervous and lose track of your thoughts during interviews, CSOAHELP’s remote interview assistance is the ultimate solution for you.

🚀 With CSOAHELP, you’ll never be stuck in an interview again—secure your dream job with confidence!

经过csoahelp的面试辅助，候选人获取了良好的面试表现。如果您需要面试辅助或面试代面服务，帮助您进入梦想中的大厂，请随时联系我。

If you need more interview support or interview proxy practice, feel free to contact us. We offer comprehensive interview support services to help you successfully land a job at your dream company.