System Design Interview Preparation

System design interviews assess your ability to design scalable, reliable systems. This guide covers core concepts and real-world scenarios for .NET developers.

Core Concepts

Scalability

Horizontal vs Vertical Scaling
Load Balancing
Caching Strategies

Reliability

Fault Tolerance
Redundancy
Health Checks

Performance

Latency Optimization
Throughput Maximization
Database Indexing

Common Patterns

Caching

When to use: Frequently accessed, rarely changing data

public async Task<Product> GetProductAsync(int id)
{
    var cacheKey = $"product:{id}";
    var cached = await _cache.GetStringAsync(cacheKey);
    
    if (cached != null)
        return JsonSerializer.Deserialize<Product>(cached);
    
    var product = await _db.Products.FindAsync(id);
    await _cache.SetStringAsync(cacheKey, JsonSerializer.Serialize(product));
    
    return product;
}

Message Queues

When to use: Async processing, decoupling services

Load Balancing

Types: Round Robin, Least Connections, IP Hash

Interview Framework

Clarify Requirements (5 min)
High-Level Design (10 min)
Deep Dive (15 min)
Bottlenecks & Trade-offs (5 min)
Scaling Strategy (5 min)