singlemaster

Singlemaster is a design pattern in distributed systems in which a single node acts as the authoritative center for writes and coordination. In this arrangement, all write operations are directed to the master, while other nodes maintain copies of the state and may handle read requests or participate in coordination depending on the system. The master’s state is replicated to follower nodes to keep them in sync.

State changes are propagated to followers through replication. Replication can be synchronous, ensuring that changes are durably recorded on the master and replicas before acknowledging a write, or asynchronous, which allows for lower latency but introduces potential lag between master and replicas. Reads can be served by replicas to improve throughput, but may observe stale data if replication lag is present.

Common use cases include traditional primary-secondary database replication, certain message brokers with a designated active broker, and distributed caches configured with a single write-enabled node. The pattern is often chosen for its simplicity and predictable write ordering, as well as easier conflict resolution since there is a single writer.

Advantages of a singlemaster design include a straightforward consistency model for writes, easy conflict resolution, and simpler recovery procedures. It also enables read scaling through replicas. However, it introduces a potential single point of failure and a bottleneck for write throughput. Failover and high availability require careful mechanisms, such as fencing to prevent split-brain, health monitoring, and automated leader election.

To mitigate downsides, systems may employ automatic failover using leader-election algorithms (for example Paxos or Raft), hot standby configurations, quorum-based decision making, or transition strategies toward multi-master or leaderless architectures that avoid a single master.