DATABASE REPLICATION.

Your database will crash. It's not a matter of if it will crash, it's when. So here's my question: is your system designed to survive it?

*One database. One crash. Total downtime. *

That's the risk you take without replication.

Here's how serious systems avoid it: a single Primary absorbs all writes while multiple Replicas serve reads in parallel. The result is faster performance, fault tolerance, and no single point of failure. When the primary goes down, a replica steps up automatically, users never feel a thing.

This is the backbone of every 24/7 application you've ever used. If backend or system designs are in your future, get comfortable with this concept now.

The tricky part is replication lag. Since syncing happens asynchronously, a replica might be milliseconds (or more) behind the primary database. If a user writes something and immediately reads it back from a replica, they might not see their own write yet.

Synchronous replication guarantees zero data loss but slows down every write. Asynchronous replication is fast but risks losing data on failover. Your startup is scaling fast and can't afford either problem. How do you architect your way out of this? I would love to hear from you.