Components

Cache
Load balancer
API gateway
User session storage (can be in a noSQL db)
Distribute(Queue)
Evaluation (logging, metrics, monitoring)

Extras

DNS
CDN
Sharding
Data Replication

Back-of-the-envelope Calculation

Estimate QPS (queries per second),DAU (daily active users) and storage requirements: \
Peek QPS = 2 * QPS \
1 Char = 1 byte, 1 Integer = 4 bytes, 1 Float = 4 bytes
1 day = 10^5 seconds
1 year = 3 x 10^7 seconds

Basic Architecture