Ec2MultiRegionSnitch
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.
The location of the cassandra.yaml file depends on the type of installation:
-
Package installations and Installer-Services installations:
/etc/dse/cassandra/cassandra.yaml -
Tarball installations and Installer-No Services installations:
<installation_location>/resources/cassandra/conf/cassandra.yaml
The location of the cassandra-rackdc.properties depends on the type of installation:
-
Package installations and Installer-Services installations:
/etc/dse/cassandra/cassandra-rackdc.properties -
Tarball installations and Installer-No Services:
installation_location/resources/cassandra/conf/cassandra-rackdc.properties
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:
-
In the
cassandra.yaml, set thelisten_addressto the private IP address of the node, and thebroadcast_addressto the public IP address of the node.This allows DataStax Enterprise (DSE) nodes in one EC2 region to bind to nodes in another region, thus enabling multiple datacenter support. For intra-region traffic, DSE switches to the private IP after establishing a connection.
-
Set the addresses of the seed nodes in the
cassandra.yamlfile to that of the public IP. Private IP are not routable between networks. For example:seeds: 50.34.16.33, 60.247.70.52To find the public IP address, from each of the seed nodes in EC2:
curl http://instance-data/latest/meta-data/public-ipv4Do not make all nodes seeds, see Internode communications (gossip).
-
Be sure that the
storage_portorssl_storage_portis 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 datacenter 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 DSE datacenters and each datacenter 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 | Node | Datacenter |
|---|---|---|
us-east |
node0 |
|
us-east |
node1 |
|
us-east |
node2 |
|
us-east |
node3 |
|
us-east |
node4 |
|
us-east |
node5 |
|
us-west |
node0 |
|
us-west |
node1 |
|
us-west |
node2 |
|
us-west |
node3 |
|
us-west |
node4 |
|
us-west |
node5 |
|
The preceding example configuration results in four datacenters in each region:
us-east_1_transactional
us-east_2_transactional
us-east_1_analytics
us-east_1_search
us-west_1_transactional
us-west_2_transactional
us-west_1_analytics
us-west_1_searchKeyspace strategy options
When defining your keyspace strategy options, use the EC2 region name, such as us-east, as your datacenter name.
