Initializing a multiple node cluster (multiple datacenters) 

A deployment scenario for a Cassandra cluster with multiple datacenters.

This topic contains information for deploying a Cassandra cluster with multiple datacenters. If you're new to Cassandra, and haven't set up a cluster, see Planning and testing cluster deployments.

This example describes installing a six node cluster spanning two datacenters. Each node is configured to use the GossipingPropertyFileSnitch (multiple rack aware) and 256 virtual nodes (vnodes).

In Cassandra, "datacenter" is synonymous with "replication group". Both terms refer to a set of nodes configured as a group for replication purposes.

Prerequisites

Each node must be correctly configured before starting the cluster. You must determine or perform the following before starting the cluster:

Procedure

  1. Suppose you install Cassandra on these nodes:
    node0 10.168.66.41 (seed1)
    node1 10.176.43.66
    node2 10.168.247.41
    node3 10.176.170.59 (seed2)
    node4 10.169.61.170
    node5 10.169.30.138
    Note: It is a best practice to have more than one seed node per datacenter.
  2. If you have a firewall running in your cluster, you must open certain ports for communication between the nodes. See Configuring firewall port access.
  3. If Cassandra is running, you must stop the server and clear the data:

    Doing this removes the default cluster_name (Test Cluster) from the system table. All nodes must use the same cluster name.

    Package installations:

    1. Stop Cassandra:
      $ sudo service cassandra stop
    2. Clear the data:
      $ sudo rm -rf /var/lib/cassandra/data/system/*

    Tarball installations:

    1. Stop Cassandra:
      $ ps auwx | grep cassandra
      $ sudo  kill pid
    2. Clear the data:
      $ sudo rm -rf /var/lib/cassandra/data/data/system/*
  4. Set the properties in the cassandra.yaml file for each node:
    Note: After making any changes in the cassandra.yaml file, you must restart the node for the changes to take effect.
    Properties to set:
    • cluster_name:
    • num_tokens: recommended value: 256
    • -seeds: internal IP address of each seed node

      In new clusters. Seed nodes don't perform bootstrap (the process of a new node joining an existing cluster.)

    • listen_address:

      If the node is a seed node, this address must match an IP address in the seeds list. Otherwise, gossip communication fails because it doesn't know that it is a seed.

      If not set, Cassandra asks the system for the local address, the one associated with its hostname. In some cases Cassandra doesn't produce the correct address and you must specify the listen_address.

    • rpc_address:listen address for client connections
    • endpoint_snitch: name of snitch (See endpoint_snitch.) If you are changing snitches, see Switching snitches.
    • auto_bootstrap: false (Add this setting only when initializing a clean node with no data.)
    Note: If the nodes in the cluster are identical in terms of disk layout, shared libraries, and so on, you can use the same cassandra.yaml file on all of them.

    Example:

    cluster_name: 'MyCassandraCluster'
    num_tokens: 256
    seed_provider:
      - class_name: org.apache.cassandra.locator.SimpleSeedProvider
        parameters:
             - seeds:  "10.168.66.41,10.176.170.59"
    listen_address:
    endpoint_snitch: GossipingPropertyFileSnitch
    Note: Include at least one node from each datacenter in the seeds list.
  5. In the cassandra-rackdc.properties file, assign the datacenter and rack names you determined in the Prerequisites. For example:

    Nodes 0 to 2 

    ## Indicate the rack and dc for this node
    dc=DC1
    rack=RAC1

    Nodes 3 to 5 

    ## Indicate the rack and dc for this node
    dc=DC2
    rack=RAC1
  6. The GossipingPropertyFileSnitch always loads cassandra-topology.properties when that file is present. Remove the file from each node on any new cluster or any cluster migrated from the PropertyFileSnitch.
  7. After you have installed and configured Cassandra on all nodes, DataStax recommends starting the seed nodes one at a time, and then starting the rest of the nodes.
    Note: If the node has restarted because of automatic restart, you must first stop the node and clear the data directories, as described above.
    Package installations:
    $ sudo service cassandra start
    Tarball installations:
    $ cd install_location 
    $ bin/cassandra
  8. To check that the ring is up and running, run:
    Package installations:
    $ nodetool status
    Tarball installations:
    $ cd install_location 
    $ bin/nodetool status

    The output should list each node, and show its status as UN (Up Normal).

    The location of the cassandra.yaml file depends on the type of installation:
    DataStax Enterprise 5.0 Installer-Services and package installations /etc/dse/cassandra/cassandra.yaml
    DataStax Enterprise 5.0 Installer-No Services and tarball installations install_location/resources/cassandra/conf/cassandra.yaml
    Cassandra package installations /etc/cassandra/cassandra.yaml
    Cassandra tarball installations install_location/resources/cassandra/conf/cassandra.yaml