Active-active is an architecture in which multiple instances or whole sites handle production requests simultaneously. If one fails, the others absorb its share, so there is no idle standby waiting to be promoted.
Why it matters
Because every node is already serving, failure causes a capacity drop rather than a cold start, and users often notice nothing. It also uses hardware efficiently and can place servers near users. The cost is complexity: state must be kept consistent across nodes, which is easy for stateless web servers and hard for databases, where simultaneous writes in two regions can conflict. Capacity planning also changes, since each node must be able to absorb a failed neighbor's load.
Example
Two data centers each run a full web tier behind a global traffic manager. Normal load is 50/50. Each site is sized to carry 100% of traffic alone:
site A: 50% normal, can take 100%
site B: 50% normal, can take 100%If site A fails its health checks, the traffic manager sends all requests to site B.
Common mistakes
- Sizing each node to 100% utilization, so a single failure overloads the survivors.
- Using active-active for the app tier while the database is still a single primary.
- Ignoring session handling, which breaks logins when a user lands on a different node.
Related
Get notified when this term updates
Plus occasional practical tips on uptime and monitoring, nothing else. Unsubscribe anytime.
This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.