Ec2MultiRegionSnitch

Use the Ec2MultiRegionSnitch for deployments on Amazon EC2 where the cluster spans multiple regions.

Use the Ec2MultiRegionSnitch for deployments on Amazon EC2 where the cluster spans multiple regions.

You must configure settings in both the cassandra.yaml file and the property file (cassandra-rackdc.properties) used by the Ec2MultiRegionSnitch.

Configuring cassandra.yaml for cross-region communication

The Ec2MultiRegionSnitch uses public IP designated in the broadcast_address to allow cross-region connectivity. Configure each node as follows:

  1. In the cassandra.yaml, set the listen_address to the private IP address of the node, and the broadcast_address to the public IP address of the node.

    This allows Cassandra nodes in one EC2 region to bind to nodes in another region, thus enabling multiple datacenter support. For intra-region traffic, Cassandra switches to the private IP after establishing a connection.

  2. Set the addresses of the seed nodes in the cassandra.yaml file to that of the public IP. Private IP are not routable between networks. For example:
    seeds: 50.34.16.33, 60.247.70.52

    To find the public IP address, from each of the seed nodes in EC2:

    $ curl http://instance-data/latest/meta-data/public-ipv4
    Note: Do not make all nodes seeds, see Internode communications (gossip).
  3. Be sure that the storage_port or ssl_storage_port is open on the public IP firewall.

Configuring the snitch for cross-region communication

In EC2 deployments, the region name is treated as the datacenter name and availability zones are treated as racks within a datacenter. For example, if a node is in the us-east-1 region, us-east is the data center name and 1 is the rack location. (Racks are important for distributing replicas, but not for datacenter naming.)

For each node, specify its datacenter in the cassandra-rackdc.properties. The dc_suffix option defines the datacenters used by the snitch. Any other lines are ignored.

In the example below, there are two cassandra datacenters and each data center is named for its workload. The datacenter naming convention in this example is based on the workload. You can use other conventions, such as DC1, DC2 or 100, 200. (datacenter names are case-sensitive.)

Region: us-east Region: us-west
Node and datacenter:
  • node0

    dc_suffix=_1_cassandra

  • node1

    dc_suffix=_1_cassandra

  • node2

    dc_suffix=_2_cassandra

  • node3

    dc_suffix=_2_cassandra

  • node4

    dc_suffix=_1_analytics

  • node5

    dc_suffix=_1_search

This results in four us-east data centers:
us-east_1_cassandra
us-east_2_cassandra
us-east_1_analytics
us-east_1_search
Node and datacenter:
  • node0

    dc_suffix=_1_cassandra

  • node1

    dc_suffix=_1_cassandra

  • node2

    dc_suffix=_2_cassandra

  • node3

    dc_suffix=_2_cassandra

  • node4

    dc_suffix=_1_analytics

  • node5

    dc_suffix=_1_search

This results in four us-west data centers:
us-west_1_cassandra
us-west_2_cassandra
us-west_1_analytics
us-west_1_search

Keyspace strategy options

When defining your keyspace strategy options, use the EC2 region name, such as us-east, as your datacenter name.

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
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