Apache Cassandra™ 2.0

Initializing a multiple node cluster (multiple data centers)

You can initialize a Cassandra cluster with multiple data centers.

If you're new to Cassandra, and haven't set up a cluster, see the Getting Started guide or 10 Minute Cassandra Walkthrough.

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

In Cassandra, the term data center is a grouping of nodes. Data center is synonymous with replication group, that is, a grouping of nodes configured together 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:
  • Install Cassandra on each node.
  • Choose a name for the cluster.
  • Get the IP address of each node.
  • Determine which nodes will be seed nodes. Do not make all nodes seeds.

    Cassandra nodes use the seed node list for finding each other and learning the topology of the ring.

  • Determine the snitch.
  • If using multiple data centers, determine a naming convention for each data center and rack, for example: DC1, DC2 or 100, 200 and RAC1, RAC2 or R101, R102. Choose the name carefully; renaming a data center is not possible.
  • Other possible configuration settings are described in The cassandra.yaml configuration file.

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 data center.
  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/system/*
  4. Set the properties in the cassandra.yaml file for each node:
    • Package installations: /etc/cassandra/conf/cassandra.yaml
    • Tarball installations: install_location/conf/cassandra.yaml
    Note: After making any changes in the cassandra.yaml file, you must restart the node for the changes to take effect.
    Properties to set:
    • num_tokens: recommended value: 256
    • -seeds: internal IP address of each seed node

      Seed nodes do not bootstrap, which is the process of a new node joining an existing cluster. For new clusters, the bootstrap process on seed nodes is skipped.

    • listen_address:

      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.

    • 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 fresh cluster 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 copy of the 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 data center.
  5. In the cassandra-rackdc.properties file, assign the data center 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. After you have installed and configured Cassandra on all nodes, start the seed nodes one at a time, and then start 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
  7. To check that the ring is up and running, run:

    Package installations:

    $ nodetool status

    Tarball installations:

    $ cd install_location 
    $ bin/nodetool status

    Each node should be listed and it's status and state should be UN (Up Normal).



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