Deploying a Cluster - Mastering Apache Cassandra - page 185

The seed node
A seed node is the one that a newly launched node consults with to learn about the cluster.
Although gossip (refer to Chapter 2 , Cassandra Architecture ) is a means for nodes to know
each other, a seed is the first node that any new node will know and start a gossip with.
Eventually, all other nodes in the cluster will know of the new node's presence and vice
versa.
There must be at least one seed node in a cluster. A seed node should be a rather stable
node. One may configure more than one seed node for added redundancy and increased
availability of seed nodes. In cassandra.yaml , seed nodes are a comma-separated list
of seed addresses:
seed_provider:
- class_name:
org.apache.cassandra.locator.SimpleSeedProvider parameters:
# Ex: "<ip1>,<ip2>,<ip3>"
- seeds: "c1.mydomain.com,c2.mydomain.com"
Listen, broadcast, and RPC addresses
A listen address is the address that nodes use to connect to each other for communication
and/or gossip. It is important to set this address to the private IP of the machine. If this is
not done, the machine will pick up the hostname value, which if incorrectly configured can
cause problems.
A broadcast address is the public address of the node. If it is not set, it will take whatever
value the listen address bears. This is generally required only if you are setting up Cas-
sandra at multiple data centers.
Note
EC2 users
For multiple data center installations, you need to use EC2 Snitch. The
listen_address may be set to blank because AWS assigns a hostname that is based on
a private IP, but you may set it to a private IP or private DNS. The broad-
cast_address must be a public IP or a public DNS. Also, remember to open stor-
age_port (default is 7000 ) in your security group that holds Cassandra instances.