Multiple Data Center Deployment¶

Prerequisites¶

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

• DataStax Enterprise is installed on each node.
• The total number of nodes in the cluster.
• A name for the cluster.
• The IP addresses of each node in the cluster.
• Which nodes will serve as the seed nodes. (DataStax Enterprise nodes use this host list to find each other and learn the topology of the ring.)
• If the nodes are behind a firewall, make sure you know what ports you need to open. See Configuring Firewall Port Access.
• Other configuration settings you may need are described in Choosing Node Configuration Options and Node and Cluster Configuration.

This information is used to configure the following properties on each node in the cluster:

• The Node and Cluster Initialization Properties in the cassandra.yaml file.
• Assigning the data center and rack names to the IP addresses of each node in the cassandra-topology.properties file.

Configuration Example¶

This example describes installing a six node cluster spanning two data centers. The steps for configuring multiple data centers on binary and packaged installations are the same except the configuration files are located in different directories.

Location of the property files in packaged installations:

• /etc/dse/cassandra/cassandra.yaml
• /etc/dse/cassandra/cassandra-topology.properties
• /etc/dse/dse.yaml

Location of the property files in binary installations:

• <install_location>/resources/cassandra/conf/cassandra.yaml
• <install_location>/resources/cassandra/conf/cassandra-topology.properties
• <install_location>/resources/dse/conf/dse.yaml

To configure a cluster with multiple data centers:

1. Suppose you install DataStax Enterprise on these nodes:

   10.168.66.41
   10.176.43.66
   10.168.247.41
   10.176.170.59
   10.169.61.170
   10.169.30.138

2. Assign tokens so that data is evenly distributed within each data center by calculating the token assignments with the Token Generating Tool and offset the token for the second data center:

   Node	IP Address	Token	Offset	Data Center
   node0	10.168.66.41	0	NA	DC1
   node1	10.176.43.66	56713727820156410577229101238628035242	NA	DC1
   node2	10.168.247.41	113427455640312821154458202477256070485	NA	DC1
   node3	10.176.170.59	10	10	DC2
   node4	10.169.61.170	56713727820156410577229101238628035252	10	DC2
   node5	10.169.30.138	113427455640312821154458202477256070495	10	DC2

For more information, see Calculating Tokens for a Multiple Data Center Cluster.

3. Stop the nodes and clear the data.

   • For packaged installs, run the following commands:

     $ sudo service dse stop (stops the service)

     $ sudo rm -rf /var/lib/cassandra/* (clears the data from the default directories)

   • For binary installs, run the following commands from the install directory:

     $ ps auwx | grep dse (finds the Cassandra and DataStax Enterprise Java process ID [PID])

     $ sudo kill <pid> (stops the process)

     $ 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:

   • initial_token: <token from previous step>
   • -seeds: <internal IP_address of each seed node>
   • listen_address: <localhost IP address>

   node0:

   initial_token: 56713727820156410577229101238628035242
   seed_provider:
      - class_name: org.apache.cassandra.locator.SimpleSeedProvider
         parameters:
           - seeds: "10.168.66.41,10.176.170.59"
   listen_address: 10.176.43.66

   Note

   You must include at least one node from each data center. It is a best practice to have at more than one seed node per data center.

node1 to node5

The properties for the rest of the nodes are the same as Node0 except for the initial_token and listen_address:

Node	initial_token	listen address
node1	56713727820156410577229101238628035242	10.176.43.66
node2	113427455640312821154458202477256070485	10.168.247.41
node3	10	10.176.170.59
node4	56713727820156410577229101238628035252	10.169.61.170
node5	113427455640312821154458202477256070495	10.169.30.138

5. For each node, change the dse.yaml file 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, enter:

   delegated_snitch: org.apache.cassandra.locator.PropertyFileSnitch

6. Determine a naming convention for each data center and rack, for example: DC1, DC2 or 100, 200 and RAC1, RAC2 or R101, R102.

7. In the cassandra-topology.properties file, 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

8. 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.

   • Packaged installs: See Starting DataStax Enterprise as a Service
   • Binary installs: See Starting DataStax Enterprise as a Stand-Alone Process

9. Check that your ring is up and running:

   • Packaged installs: nodetool ring -h localhost
   • Binary installs:

   $ cd /<install_directory>
   $ bin/nodetool ring -h localhost