Adding nodes to an existing cluster
Steps to add nodes when using virtual nodes.
Virtual nodes (vnodes) greatly simplify adding nodes to an existing cluster:
- Calculating tokens and assigning them to each node is no longer required.
- Rebalancing a cluster is no longer necessary because a node joining the cluster assumes responsibility for an even portion of the data.
For a detailed explanation about how this works, see Virtual nodes.
If you are using racks, you can safely bootstrap two nodes at a time when both nodes are on the same rack.
- Install Cassandra on the new nodes, but do not start Cassandra.
Set the following properties in the
cassandra.yaml and, depending on the snitch, the
cassandra-rackdc.properties configuration files:
- auto_bootstrap - If this option has been set to false, you must set it to true. This option is not listed in the default cassandra.yaml configuration file and defaults to true.
- cluster_name - The name of the cluster the new node is joining.
- listen_address/broadcast_address - May usually be left blank. Otherwise, use IP address or host name that other Cassandra nodes use to connect to the new node.
- endpoint_snitch - The snitch Cassandra uses for locating nodes and routing requests.
- num_tokens - The number of vnodes to assign to the node. If the hardware capabilities vary among the nodes in your cluster, you can assign a proportional number of vnodes to the larger machines.
- seed_provider - The -seeds list in this setting determines which nodes the new node should contact to learn about the cluster and establish the gossip process.
- Change any other non-default settings you have made to your existing cluster in the cassandra.yaml file and cassandra-topology.properties or cassandra-rackdc.properties files. Use the diff command to find and merge (by head) any differences between existing and new nodes.
- Start Cassandra on each new node. Allow two minutes between node initializations. You can monitor the startup and data streaming process using nodetool netstats.
After all new nodes are running, run nodetool cleanup on each of
the previously existing nodes to remove the keys no longer belonging to those
nodes. Wait for cleanup to complete on one node before doing the next.
Cleanup may be safely postponed for low-usage hours.