<strong>Redundancy</strong> means having backup copies of critical components. If one fails, another takes over immediately, preventing downtime.
The Backup Pilot
Like having a co-pilot ready to take over if the pilot can't fly, redundancy ensures backup systems are ready.
Main Pilot
Primary system
Co-Pilot
Backup ready
Safety
No single point of failure
Primary
Backup (ready)
No downtime
Deploy Duplicates
Run multiple copies of servers, databases, etc.
Sync Data
Keep backups updated with latest data
Monitor Health
Constantly check if primary is working
Detect Failure
Notice when primary goes down
Automatic Failover
Backup takes over instantly
Wrong
Redundancy is wasteful because backup servers sit idle
Correct
Backups can handle traffic too (load balancing). Even if idle, the cost of downtime (lost revenue, angry users) far exceeds the cost of redundancy.
Netflix redundancy:
Multiple data centers across regions
If US-East-1 fails, traffic goes to US-West-2
Database has 3 replicas minimum
Critical services run on multiple servers
You never notice when one server fails