Using multiple network interfaces

Steps for configuring DataStax Distribution of Apache Cassandra™ (DDAC) for multiple network interfaces or when using different regions in cloud implementations.

You must configure settings in both the file and the relevant property file:

cassandra-rackdc.properties

The cassandra-rackdc.properties file is located in the installation_location/conf directory.

cassandra.yaml

The cassandra.yaml file is located in the installation_location/conf directory.

Configuring cassandra.yaml for multiple networks or across regions in cloud implementations

In multiple networks or cross-region cloud scenarios, communication between datacenters can only take place using an external IP address. The external IP address is defined in the cassandra.yaml file using the broadcast_address setting. Configure each node as follows:

In the cassandra.yaml file , set the listen_address to the private IP address of the node, and the broadcast_address to the public address of the node.
This allows nodes to bind to nodes in another network or region, thus enabling multiple datacenter support. For intra-network or region traffic, Cassandra switches to the private IP after establishing a connection.
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
```
Note: Do not make all nodes seeds, see Internode communications (gossip).
Be sure that the storage_port or ssl_storage_port is open on the public IP firewall.

Additional cassandra.yaml configuration for non-EC2 implementations

If multiple network interfaces are used in a non-EC2 implementation, enable the

listen_on_broadcast_address

option.

listen_on_broadcast_address: true

In non-EC2 environments, the public address to private address routing is not automatically enabled. Enabling listen_on_broadcast_address allows Cassandra to listen on both listen_address and broadcast_address with two network interfaces.

Configuring the snitch for multiple networks

External communication between the datacenters can only happen when using the broadcast_address (public IP).

The GossipingPropertyFileSnitch is recommended for production. The cassandra-rackdc.properties file defines the datacenters used by this snitch. Enable the option prefer_local to ensure that traffic to broadcast_address will re-route to listen_address.

For each node in the network, specify its datacenter in cassandra-rackdc.properties file.

In the example below, there are two datacenters. You can use any naming convention, such as DC1, DC2 or 100, 200. (Datacenter names are case-sensitive.


Network A	Network B
Node and datacenter: node0 dc=DC_A_transactional rack=RAC1 node1 dc=DC_A_transactional rack=RAC1 node2 dc=DC_B_transactional rack=RAC1 node3 dc=DC_B_transactional rack=RAC1 node4 dc=DC_A_transactional rack=RAC1	Node and datacenter: node0 dc=DC_A_transactional rack=RAC1 node1 dc=DC_A_transactional rack=RAC1 node2 dc=DC_B_transactional rack=RAC1 node3 dc=DC_B_transactional rack=RAC1 node4 dc=DC_A_transactional rack=RAC1 node5 dc=DC_A_analytics rack=RAC1

Configuring the snitch for cross-region communication in cloud implementations

Note: Be sure to use the appropriate snitch for your implementation. If deploying on Amazon EC2, see the instructions in Ec2MultiRegionSnitch.

In cloud 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 datacenter name and 1 is the rack location. (Racks are important for distributing replicas, but not for datacenter naming.)

In the example below, there are two datacenters. You can use any naming convention, such as DC1, DC2 or 100, 200. (Datacenter names are case-sensitive.

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.


Region: us-east	Region: us-west
Node and datacenter: node0 `dc_suffix=_1_transactional` node1 `dc_suffix=_1_transactional` node2 `dc_suffix=_2_transactional` node3 `dc_suffix=_2_transactional` This results in four us-east datacenters: `us-east_1_transactional us-east_2_transactional`	Node and datacenter: node0 `dc_suffix=_1_transactional` node1 `dc_suffix=_1_transactional` node2 `dc_suffix=_2_transactional` node3 `dc_suffix=_2_transactional` This results in four us-west datacenters: `us-west_1_transactional us-west_2_transactional`