System Design Course – APIs, Databases, Caching, CDNs, Load Balancing & Production Infra

Architectural thinking separates seniors from mid-level developers

Companies pay senior engineers for designing systems from scratch and making trade-off decisions, not just writing code to existing specifications.

Start with a single-server architecture to understand core components

Begin with one server handling web tier, database, and cache to visualize request flow from DNS resolution through HTTP requests before adding complexity.

Web and mobile clients interact with servers differently

Web browsers receive HTML/CSS/JS for rendering while mobile apps typically consume JSON API responses over HTTP for lightweight data interpretation.

SQL databases excel at structured data and transactional integrity

Relational databases like PostgreSQL and MySQL use ACID-compliant transactions and complex joins, making them ideal for banking systems and structured e-commerce data.

NoSQL offers four specialized database types for different use cases

Document stores (MongoDB), wide-column (Cassandra), graph (Neo4j), and key-value (Redis) databases provide flexibility and speed for unstructured data at massive scale.

Choose databases based on data structure and consistency requirements

Use SQL for structured data requiring strong consistency and NoSQL for low-latency, flexible storage of semi-structured data like user activity logs.

Vertical scaling hits hard limits and creates single points of failure

Adding CPU/RAM to a single server is simple but eventually reaches hardware caps and offers no redundancy if the server crashes.

Horizontal scaling enables fault tolerance through multiple servers

Distributing load across multiple servers allows continuous operation during individual server failures and supports growth by adding nodes rather than upgrading hardware.

Load balancers distribute traffic using algorithms like round robin

Load balancers sit between clients and server pools to route requests sequentially across available servers and automatically stop sending traffic to failed nodes.