Inventory management in HLD - Architecture Diagram

System Overview - Inventory management

This system helps businesses keep track of their products and stock levels. It allows users to add, update, and check inventory items quickly and reliably. The system must handle many users and keep data accurate and up-to-date.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  v
Inventory Service
  |
  +-----> Cache
  |
  v
Database

Components

User

client

Person or system interacting with the inventory system

Load Balancer

load_balancer

Distributes incoming user requests evenly to prevent overload

API Gateway

api_gateway

Handles request routing, authentication, and rate limiting

Inventory Service

service

Processes inventory operations like add, update, and query

Cache

cache

Stores frequently accessed inventory data for faster reads

Database

database

Stores all inventory data persistently and reliably

Request Flow - 11 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Inventory Service

Inventory Service → Cache

Cache → Inventory Service

Inventory Service → Database

Database → Inventory Service

Inventory Service → Cache

Inventory Service → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Database

Impact:New writes to inventory fail; reads may still succeed if data is cached

Mitigation:Use database replication for failover; rely on cache for read requests temporarily

Architecture Quiz - 3 Questions

Which component handles user authentication before processing inventory requests?

A API Gateway

B Load Balancer

C Cache

D Inventory Service

Design Principle

This design uses a layered approach with caching to improve read performance and a load balancer to distribute traffic evenly. The API Gateway centralizes security and routing, ensuring scalability and maintainability.

Practice

1. Which component is essential in an inventory management system to keep track of all products and their details?

easy

A. Product catalog

B. User authentication

C. Payment gateway

D. Notification service

Solution

1. Step 1: Understand the role of components in inventory management

   The product catalog stores all product details like name, ID, and description.

2. Step 2: Identify the component that tracks products

   Only the product catalog directly manages product information essential for inventory.

3. Final Answer:

   Product catalog -> Option A

4. Quick Check:

   Product catalog = Tracks products [OK]

Hint: Product catalog holds product info, key for inventory [OK]

Common Mistakes:

• Confusing payment gateway with product tracking
• Thinking user authentication manages products
• Assuming notification service stores product data

2. Which of the following is the correct way to represent a stock update transaction in an inventory system?

easy

A. {"product_id": 101, "change": +5}

B. {"id": 101, "stock": "increase"}

C. {"product": 101, "update": "add"}

D. {"item": 101, "quantity": "plus"}

Solution

1. Step 1: Analyze the transaction format for clarity and correctness

   The transaction should clearly identify the product and the numeric change in stock.

2. Step 2: Compare options for proper keys and value types

   {"product_id": 101, "change": +5} uses clear keys and a numeric change (+5) which is standard for stock updates.

3. Final Answer:

   {"product_id": 101, "change": +5} -> Option A

4. Quick Check:

   Numeric change with product_id = Correct format [OK]

Hint: Use numeric change with product_id for stock updates [OK]

Common Mistakes:

• Using string values instead of numeric for stock change
• Using unclear keys like 'item' or 'update'
• Missing product identification key

3. Given this simplified flow: A product stock is 10 units. A transaction reduces stock by 3 units, then another adds 5 units. What is the final stock?

medium

A. 15 units

B. 12 units

C. 8 units

D. 10 units

Solution

1. Step 1: Apply the first transaction reducing stock

   Starting stock is 10 units. Reducing by 3 units gives 10 - 3 = 7 units.

2. Step 2: Apply the second transaction adding stock

   Adding 5 units to 7 units results in 7 + 5 = 12 units.

3. Final Answer:

   12 units -> Option B

4. Quick Check:

   10 - 3 + 5 = 12 [OK]

Hint: Add and subtract transactions stepwise to find final stock [OK]

Common Mistakes:

• Adding before subtracting stock
• Ignoring one of the transactions
• Confusing initial stock with final stock

4. In an inventory system, a stock update transaction sometimes fails to update the stock count correctly. Which is the most likely cause?

medium

A. Missing transaction logging

B. User interface color mismatch

C. Race condition on stock updates

D. Incorrect product catalog data

Solution

1. Step 1: Understand common causes of incorrect stock updates

   Race conditions happen when multiple updates happen simultaneously without proper locking.

2. Step 2: Identify the cause that directly affects stock count accuracy

   Race condition can cause lost updates, leading to incorrect stock counts.

3. Final Answer:

   Race condition on stock updates -> Option C

4. Quick Check:

   Race condition = Incorrect stock update [OK]

Hint: Concurrent updates need locking to avoid race conditions [OK]

Common Mistakes:

• Blaming UI issues for backend stock errors
• Ignoring concurrency problems
• Assuming logging affects stock accuracy

5. You design an inventory system for a large retailer with thousands of products and frequent stock changes. Which design choice best ensures scalability and accuracy?

hard

A. Use manual stock updates by warehouse staff only

B. Use distributed caches with eventual consistency for stock counts

C. Use a centralized database with strong locking for all stock updates

D. Use event-driven architecture with message queues and atomic updates

Solution

1. Step 1: Consider scalability and accuracy needs

   Large scale with frequent updates requires a system that handles concurrency and scales well.

2. Step 2: Evaluate design options for best fit

   Event-driven architecture with message queues allows asynchronous, atomic updates and scales horizontally.

3. Final Answer:

   Use event-driven architecture with message queues and atomic updates -> Option D

4. Quick Check:

   Event-driven + atomic updates = Scalable & accurate [OK]

Hint: Event-driven with atomic updates scales best for inventory [OK]

Common Mistakes:

• Choosing centralized locking which limits scalability
• Relying on eventual consistency causing stock errors
• Using manual updates which are slow and error-prone