White List Policy

The White List load balancing policy wraps a subpolicy and ensures that only hosts from a provided white list are used. This policy can be used to limit effects of automatic peer discovery to executing queries only on a given set of hosts.

Prevent queries from running on non-whitelisted hosts

Given

a running cassandra cluster with schema:

CREATE KEYSPACE simplex WITH replication = {'class': 'SimpleStrategy', 'replication_factor': 3};
USE simplex;
CREATE TABLE songs (
  id uuid PRIMARY KEY,
  title text,
  album text,
  artist text,
  tags set<text>,
  data blob
);
INSERT INTO songs (id, title, album, artist, tags)
VALUES (
   756716f7-2e54-4715-9f00-91dcbea6cf50,
   'La Petite Tonkinoise',
   'Bye Bye Blackbird',
   'Joséphine Baker',
   {'jazz', '2013'})
;
INSERT INTO songs (id, title, album, artist, tags)
VALUES (
   f6071e72-48ec-4fcb-bf3e-379c8a696488,
   'Die Mösch',
   'In Gold',
   'Willi Ostermann',
   {'kölsch', '1996', 'birds'}
);
INSERT INTO songs (id, title, album, artist, tags)
VALUES (
   fbdf82ed-0063-4796-9c7c-a3d4f47b4b25,
   'Memo From Turner',
   'Performance',
   'Mick Jager',
   {'soundtrack', '1991'}
);

And

the following example:

require 'cassandra'

allowed_ips = ["127.0.0.1", "127.0.0.3"]
round_robin = Cassandra::LoadBalancing::Policies::RoundRobin.new
whitelist   = Cassandra::LoadBalancing::Policies::WhiteList.new(allowed_ips, round_robin)
cluster     = Cassandra.cluster(load_balancing_policy: whitelist)
session     = cluster.connect('simplex')

coordinator_ips = 3.times.map do
  info = session.execute("SELECT * FROM songs").execution_info
  info.hosts.last.ip
end

puts coordinator_ips.sort.uniq

When

it is executed

Then

its output should contain:

127.0.0.1
127.0.0.3