Extended the single-node log to work across multiple nodes with consistent ordering. Now we need to ensure all nodes see the same log sequence!
What it Does
- Distribute log operations across multiple nodes
- Maintain consistent offset ordering globally
- Replicate log entries for fault tolerance
- Coordinate consumer offset commits
The Challenge
Multi-node logs need:
- Global Ordering: All nodes must agree on message sequence
- Consistency: Same offset = same message everywhere
- Coordination: Who assigns the next offset?
- Replication: How do we ensure durability?
The Approach
- Leader Election: One node coordinates offset assignment
- Log Replication: Leaders replicate to followers
- Consistent Reads: Route reads through current leader
- Failover: Handle leader failures gracefully
Key Operations
- Send: Forward to leader for offset assignment
- Poll: Can read from any replica
- Commit: Coordinate across nodes
- Sync: Replicate log entries
Coordination Patterns
- Centralized offset generation for consistency
- Async replication for performance
- Read-your-writes consistency
- Graceful leader failover
Trade-offs
Pros:
- Strong consistency guarantees
- Fault tolerant through replication
- Clear ordering semantics
Cons:
- More complex than single node
- Leader bottleneck for writes
- Network coordination overhead
This gets us closer to real distributed log systems - the patterns here show up in Kafka, distributed databases, and consensus systems.
