Consistent Hashing Ring Lab (Interactive)
Add and remove cache nodes and watch only K/N keys rebalance. Experiment with consistent hashing rings, virtual nodes (vNodes), and hash distribution. Understand how Discord, DynamoDB, and Cassandra scale without massive cache stampedes.
Consistent Hashing Ring Simulator
Visualize how consistent hashing moves only K/N keys during cluster scale-up/down.
Node Key Distribution (6 Total Keys)
› Initialized ring with 3 physical nodes and 6 keys.
How It Works Under the Hood
In traditional modulo hashing (hash(key) % N), adding or removing a single node changes the denominator from N to N±1. This causes virtually 100% of all keys to remap to different servers simultaneously, instantly evicting caches and triggering catastrophic database brownouts (cache stampedes). Consistent hashing maps both servers and keys onto a contiguous 360-degree integer ring [0, 2^32 - 1]. A key is assigned to the first server encountered clockwise along the ring. When a server node is added or removed, only keys residing between that node and its predecessor are re-assigned—exactly K/N keys on average, where K is total keys and N is total servers. Virtual nodes (vNodes) replicate each physical machine across multiple distinct positions on the hash ring to eliminate hot spots and guarantee uniform key distribution.
Core Architectural Principles
- Both keys and server identifiers are hashed into the same uniform 32-bit or 64-bit integer space [0, 2^32-1].
- Lookups operate via binary search clockwise along the sorted ring of active node tokens in O(log N) time.
- Virtual nodes (vNodes): Each physical host is hashed multiple times (e.g., node-1#1, node-1#2) to balance load variance.
- Failure isolation: When a node dies, only its immediate clockwise segment fails over to the next neighbor.
In system design interviews, never say "just add a hash function." Specifically specify consistent hashing with virtual nodes. When asked how many keys move when a node joins or leaves, state with confidence: "Only about K/N keys are moved, whereas traditional modulo hashing redistributes nearly K keys."
Slight memory and binary search lookup overhead on the client router vs massive resilience against cluster rebalancing stampedes.