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 vnodes work, see Virtual nodes.

Note: If you do not use vnodes, see Adding single-token nodes to a cluster.

Procedure

Be sure to use the same version of Cassandra on all nodes in the cluster.
  1. Install Cassandra on the new nodes, but do not start Cassandra.

    If your Cassandra installation on Debian installation starts automatically, you must stop the node and clear the data.

  2. Depending on the snitch used in the cluster, set either the properties in the cassandra-topology.properties or the cassandra-rackdc.properties file:
    The location of the cassandra-topology.properties file depends on the type of installation:
    Package installations /etc/cassandra/cassandra-topology.properties
    Tarball installations install_location/conf/cassandra-topology.properties
    The location of the cassandra-rackdc.properties file depends on the type of installation:
    Package installations /etc/cassandra/cassandra-rackdc.properties
    Tarball installations install_location/conf/cassandra-rackdc.properties
  3. Set the following properties in the cassandra.yaml file:
    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
    Can 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
    Make sure that the new node lists at least one node in the existing cluster. The -seeds list determines which nodes the new node should contact to learn about the cluster and establish the gossip process.
    Note: Seed nodes cannot bootstrap. Make sure the new node is not listed in the -seeds list. Do not make all nodes seed nodes. Please read Internode communications (gossip).
    Other non-default settings
    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 any differences between existing and new nodes.
    The location of the cassandra.yaml file depends on the type of installation:
    Package installations /etc/cassandra/cassandra.yaml
    Tarball installations install_location/resources/cassandra/conf/cassandra.yaml
  4. Start the bootstrap node.
  5. Use nodetool status to verify that the node is fully bootstrapped and all other nodes are up (UN) and not in any other state.
  6. After all new nodes are running, run nodetool cleanup on each of the previously existing nodes to remove the keys that no longer belong to those nodes. Wait for cleanup to complete on one node before running nodetool cleanup on the next node.

    Cleanup can be safely postponed for low-usage hours.