Multiple data centers
Play this lessonThis lesson comes with an interactive animation you can break and a chapter quiz.As your site gets popular internationally, you add more data centers for better availability and speed. Users are geoDNS-routed (geo-routed) to the closest one: geoDNS resolves the domain to different IPs depending on where the user is. Traffic is split, say x% to US-East and (100 − x)% to US-West.
If a whole data center goes down, all traffic is sent to a healthy one.
Technical challenges
- Traffic redirection: tools like GeoDNS send users to the nearest healthy data center.
- Data synchronization: users in different regions may use different local databases or caches. During a failover, traffic can land where the data isn't. The usual fix is to replicate data across data centers (Netflix does asynchronous multi-data-center replication).
- Test and deployment: test the app in every location, and use automated deployment tools to keep services consistent everywhere.
Key takeaways
- geoDNS routes users to the closest data center.
- On an outage, 100% of traffic goes to the healthy data center.
- Hard parts: redirection, data sync, deployment.