What is a seed node in Apache Cassandra?

Seed nodes serve two purposes in cassandra: 1. They allow the instance to find the cluster on the very first startup, and 2. They assist in gossip convergence. read more

So a cluster is defined by some initial nodes which are available at clear addresses and they become a reference for that cluster for any new nodes to join in trustable way. The seed nodes can go away after some time, the cluster will keep on. The clear information is such as Apache Cassandra Tutorial. read more

seed nodes act as gossip hot spots. since nodes gossip more often with seeds than non-seeds, the seeds tend to have more current information, and therefore the whole cluster has more current information. this is the reason you should not make all nodes seeds. similarly, this is also why all nodes in a given data center should have the same list of seed nodes in their cassandra.yaml file. typically, 3 seed nodes per data center is ideal. read more

From the Cassandra docs: Note: The seed node designation has no purpose other than bootstrapping the gossip process for new nodes joining the cluster. Seed nodes are not a single point of failure, nor do they have any other special purpose in cluster operations beyond the bootstrapping of nodes. read more