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Multi-leader replication

Each region accepts writes for the same data and copies them to the others, so two regions can take conflicting writes that must be settled.

Taught in Chapter 23: Availability.

More from the same chapter

• Availability: The share of time or requests a system serves correctly, usually counted in nines.
• CRDT: A data type built so concurrent changes always merge the same way, such as a counter that adds every region's increments.
• Failover: Promoting a replica to take over when the primary dies, then sending writes to it.
• Fencing: Cutting the old primary off before promoting a replica, so two nodes can't both accept writes.
• Health check: A load balancer's regular probe of each target; failing ones are taken out of rotation.
• Last writer wins: Settling conflicting writes by keeping the one with the newest timestamp. The other is dropped without an error.
• Redundancy: Running spares of each part, so one can fail while another serves.
• Single point of failure: Any part whose loss takes the whole system down.
• SLI, SLO and SLA: What you measure, the goal for it, and a promise to customers with a penalty attached.
• Split brain: Two nodes both acting as primary and accepting writes; prevented by fencing the old one.