DataStax Enterprise 3.2

Multiple data center deployment

In this scenario, a mixed workload cluster has more than one data center for each type of node. For example, if the cluster has 4 Hadoop nodes, 4 Cassandra nodes, and 2 Solr nodes, the cluster could have 5 data centers: 2 data centers for Hadoop nodes, 2 data centers for Cassandra nodes, and 1 data center for Solr nodes. A single data center cluster has only 1 data center for each type of node

In multiple data center deployments, data replication can be distributed across multiple, geographically dispersed data centers; between different physical racks in a data center; or between public cloud providers and on-premise managed data centers. Data replicates across the data centers automatically and transparently. No ETL work is necessary to move data between different systems or servers. You can configure the number of copies in each data center and Cassandra handles the rest, replicating the data for you. For more information about replication:

To configure a single data center cluster, see Single data center deployment.

Prerequisites

To configure a multi-node cluster with multiple data centers:

  • DataStax Enterprise is installed on each node.
  • Choose a name for the cluster.
  • For a mixed-workload cluster, determine the purpose of each node.
  • Get the IP address of each node.
  • Determine which nodes are seed nodes. (Seed nodes provide the means for all the nodes find each other and learn the topology of the ring.)
  • Develop a naming convention for each data center and rack, for example: DC1, DC2 or 100, 200 and RAC1, RAC2 or R101, R102.
  • Other possible configuration settings are described in the cassandra.yaml configuration file.
  • Set virtual nodes correctly for the type of data center. DataStax recommends using virtual nodes only on data centers running purely Cassandra workloads. See Setting up virtual nodes in About virtual nodes.

In DataStax Enterprise 3.0.1 and later, the default consistency level has changed from ONE to QUORUM for reads and writes. This change resolves the problem of finding a CassandraFS block when using consistency level ONE on a Hadoop node.

Procedure

This configuration example describes installing a six node cluster spanning two data centers.

Set properties for each node in the cassandra.yaml file. This file is located in different places depending on the type of installation:

Packaged installs:
  • /etc/dse/cassandra/cassandra.yaml
  • /etc/dse/cassandra/cassandra-topology.properties
  • /etc/dse/dse.yaml
Tarball installs:
  • install_location/resources/cassandra/conf/cassandra.yaml
  • install_location/resources/cassandra/conf/cassandra-topology.properties
  • install_location/resources/dse/conf/dse.yaml
Note: After making any changes in the cassandra.yaml file, you must restart the node for the changes to take effect.

  1. Suppose you install DataStax Enterprise 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
  2. If the nodes are behind a firewall, open the required ports for internal/external communication. See Configuring firewall port access.
  3. If DataStax Enterprise is running, stop the nodes and clear the data:
    • Packaged installs:
      $ sudo service dse stop
      $ sudo rm -rf /var/lib/cassandra/* ## Clears the data from the  default directories
    • Tarball installs:

      From the install directory:

      $ sudo bin/dse cassandra-stop
      $ sudo rm -rf /var/lib/cassandra/* ## Clears the data from the default directories
  4. Modify the following property settings in the cassandra.yaml file for each node:
    • num_tokens: 256 for Cassandra nodes
    • num_tokens: 1 for Hadoop and Solr nodes
    • -seeds: internal_IP_address of each seed node
    • listen_address: localhost_IP_address
    • auto_bootstrap: false (Add this setting only when initializing a fresh cluster with no data.)
    • Make sure that the following options are disabled, as they are no longer supported by DataStax Enterprise:
      ## Replication strategy to use for the auth keyspace.
      #auth_replication_strategy: org.apache.cassandra.locator.SimpleStrategy
      
      #auth_replication_options:
      #replication_factor: 1
      
      Note: If you have not disabled both auth_replication_strategy and replication_factor, you will see an error. For information about correcting this error, see Issues in the DataStax Enterprise 3.2.5 release notes.

    node0:

    cluster_name: 'MyDemoCluster'
    num_tokens: 256
    seed_provider:
      - class_name: org.apache.cassandra.locator.SimpleSeedProvider
        parameters:
             - seeds: "10.168.66.41,10.176.170.59"
    listen_address: 10.168.66.41
    Note: You must include at least one node from each data center. It is a best practice to have more than one seed node per data center.

    The properties for rest of the nodes are the same as node0 except for the listen_address:

    Node listen_address
    node1 10.176.43.66
    node2 10.168.247.41
    node3 10.176.170.59
    node4 10.169.61.170
    node5 10.169.30.138
  5. If necessary, change the dse.yaml file on each node to specify the snitch to be delegated by the DseDelegateSnitch. For more information about snitches, see the About Snitches. For example, to specify the PropertyFileSnitch:
    delegated_snitch: org.apache.cassandra.locator.PropertyFileSnitch
  6. In the cassandra-topology.properties file, use your naming convention to assign data center and rack names to the IP addresses of each node, and assign a default data center name and rack name for unknown nodes. For example:
    # Cassandra Node IP=Data Center:Rack
    10.168.66.41=DC1:RAC1
    10.176.43.66=DC2:RAC1
    10.168.247.41=DC1:RAC1
    10.176.170.59=DC2:RAC1
    10.169.61.170=DC1:RAC1
    10.169.30.138=DC2:RAC1
    
    # default for unknown nodes
    default=DC1:RAC1
  7. After you have installed and configured DataStax Enterprise 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 stop the node and clear the data directories, as described above.
  8. Check that your cluster is up and running:
    • Packaged installs: $ nodetool status
    • Tarball installs: $ install_location/bin/nodetool status

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