What happens when all seed nodes in Cassandra are down? Can new nodes join the cluster at that point?

Question

What happens when all seed nodes in Cassandra are down? Can new nodes join the cluster at that point ?

Answer 1

This is from cassandra docs

The ring can operate or boot without a seed; however, you will not be able to add new nodes to the cluster. It is recommended to configure multiple seeds in production system. `

Here is the link http://cassandra.apache.org/doc/latest/faq/index.html#does-single-seed-mean-single-point-of-failure

Answer 2

The seed nodes are the initial point of contact for bootstrapping nodes. If you have a cluster of say 10 nodes you can ideally might have say 3 nodes as seeds. Once the bootstrapping node contacts the seed it will then start to gossip with other nodes.

There is nothing special about a seed node in terms of its functionality, it will operate exactly the same as other nodes (seed nodes do gossip more though see doc link below)

So if per chance your 3 seed nodes were down you could just add an IP of any other node in the cluster to your new node under the seeds: parameter in the cassandra.yaml file and you'll still be able to bootstrap.

It is of course nice to have all nodes using the same seeds like, for purposes of configuration consistency.

https://docs.datastax.com/en/cassandra/2.1/cassandra/configuration/configCassandra_yaml_r.html#reference_ds_qfg_n1r_1k__seed_provider