Scale after simpler fixes are exhausted.

Goal

Teach scale as a sequence of tradeoffs.

This phase should make clear that scale is not one tool. It is a set of decisions about reads, writes, consistency, costs, failure modes, and team capacity.

Build

• Read replicas for read-heavy endpoints.
• Partitioning for large tables.
• Separate services only where ownership and bottlenecks justify it.
• Sharding discussion after indexes, caching, replicas, and partitioning are understood.

Concepts

• Distributed systems.
• Replication lag.
• Consistency and CAP tradeoffs.
• Data partitioning.
• Service boundaries and operational cost.

Prompt stub

Evaluate the current system for scaling bottlenecks.
Do not jump straight to microservices or sharding.
Explain what we should measure first and which simpler fixes come before distributed architecture.

Done means

• The learner understands the cost of every scaling tool introduced.
• The course can explain why Reddit-scale architecture was not used on day one.
• The app has a plausible path from low traffic to serious traffic.
• Future rewrites are tied to measured pressure, not architecture theater.