= cassandra-rackdc.properties file

Several `snitch` options use the `cassandra-rackdc.properties`
configuration file to determine which `datacenters` and racks cluster
nodes belong to. Information about the network topology allows requests
to be routed efficiently and to distribute replicas evenly. The
following snitches can be configured here:

* GossipingPropertyFileSnitch
* AWS EC2 single-region snitch
* AWS EC2 multi-region snitch

The GossipingPropertyFileSnitch is recommended for production. This
snitch uses the datacenter and rack information configured in a local
node's `cassandra-rackdc.properties` file and propagates the information
to other nodes using `gossip`. It is the default snitch and the settings
in this properties file are enabled.

The AWS EC2 snitches are configured for clusters in AWS. This snitch
uses the `cassandra-rackdc.properties` options to designate one of two
AWS EC2 datacenter and rack naming conventions:

* legacy: Datacenter name is the part of the availability zone name
preceding the last "-" when the zone ends in -1 and includes the number
if not -1. Rack name is the portion of the availability zone name
following the last "-".
+
____
Examples: us-west-1a => dc: us-west, rack: 1a; us-west-2b => dc:
us-west-2, rack: 2b;
____
* standard: Datacenter name is the standard AWS region name, including
the number. Rack name is the region plus the availability zone letter.
+
____
Examples: us-west-1a => dc: us-west-1, rack: us-west-1a; us-west-2b =>
dc: us-west-2, rack: us-west-2b;
____

Either snitch can set to use the local or internal IP address when
multiple datacenters are not communicating.

== GossipingPropertyFileSnitch

=== `dc`

Name of the datacenter. The value is case-sensitive.

*Default value:* DC1

=== `rack`

Rack designation. The value is case-sensitive.

*Default value:* RAC1

== AWS EC2 snitch

=== `ec2_naming_scheme`

Datacenter and rack naming convention. Options are `legacy` or
`standard` (default). *This option is commented out by default.*

*Default value:* standard

[NOTE]
.Note
====
YOU MUST USE THE `legacy` VALUE IF YOU ARE UPGRADING A PRE-4.0 CLUSTER.
====

== Either snitch

=== `prefer_local`

Option to use the local or internal IP address when communication is not
across different datacenters. *This option is commented out by default.*

*Default value:* true