Horizontal scaling vs Vertical scaling
Horizontal scaling means that you scale by adding more machines into your pool of resources whereas Vertical scaling means that you scale by adding more power (CPU, RAM) to an existing machine
Load Balancing
Load banlancer has pub IP, and route the requests to certain server. End servers have private IPs.(private IPs increase privacy since cannot be contact directly;IPv4 address shortage)
Cache
DNS has TTL(time to live)