Cassandra Cluster with six\u00a0nodes.<\/p>\n
- \n
- AZ-1a: us-east-1a: Node 1, Node 2<\/li>\n
- AZ-1b: us-east-1b: Node 3, Node 4<\/li>\n
- AZ-1c: us-east-1c: Node 5, Node 6<\/li>\n<\/ul>\n
Next, we have to make changes in the Cassandra configuration file. cassandra.yaml<\/em> file is the main configuration file for Cassandra. We can control how nodes are configured within a cluster, including inter-node communication, data partitioning and replica placement etc., in this config file. The key value which we need to define in the config file in this context is called Snitch<\/em>. Basically, a snitch<\/em> indicates as to which Region and Availability zones does each node in the cluster belongs to. It gives information about the network topology so as to the requests are routed efficiently. Additionally, Cassandra has replication strategies which place the replicas based on the information provided by the snitch. There are different types of snitches available. But, in this case, we shall use EC2Snitch<\/em> as all of our nodes in the cluster are within a single region.<\/p>\n
We shall set the snitch value as shown below:
![\"snitch\"](\"https:\/\/content.cloudthat.com\/resources\/wp-content\/uploads\/2022\/11\/snitch.png\")
<\/a><\/p>\nAlso, since we are using multiple nodes, we need to group our nodes. We shall do so, by defining seeds<\/em> key in the configuration file (Cassandra.yaml) . Cassandra nodes use seeds for finding each other and learning the topology of the ring. It is used during startup to discover the cluster.<\/p>\n
For instance:<\/p>\n
Node 1: <\/strong>Set the seeds<\/em> value as shown below:
![\"node1\"](\"https:\/\/content.cloudthat.com\/resources\/wp-content\/uploads\/2022\/11\/node1.png\")
<\/a><\/p>\nSimilarly on the other nodes:<\/p>\n
Node 2:<\/strong><\/p>\n
![\"node2\"](\"https:\/\/content.cloudthat.com\/resources\/wp-content\/uploads\/2022\/11\/node2.png\")
<\/a><\/p>\nNode 3:<\/strong><\/p>\n
![\"node3\"](\"https:\/\/content.cloudthat.com\/resources\/wp-content\/uploads\/2022\/11\/node3.png\")
<\/a><\/p>\nNode 4:<\/strong><\/p>\n
![\"node4\"](\"https:\/\/content.cloudthat.com\/resources\/wp-content\/uploads\/2022\/11\/node4.png\")
<\/a><\/p>\nNode 5:<\/strong><\/p>\n
![\"node5\"](\"https:\/\/content.cloudthat.com\/resources\/wp-content\/uploads\/2022\/11\/node5.png\")
<\/a><\/p>\nNode 6:<\/strong><\/p>\n
![\"node6\"](\"https:\/\/content.cloudthat.com\/resources\/wp-content\/uploads\/2022\/11\/node6.png\")
<\/a><\/p>\nCassandra nodes use this list of hosts to find each other and learn the topology of the ring. The nodetool<\/em> utility is a command line interface for managing a cluster. We shall check the status of the cluster using this command as shown below:
![\"cass\"](\"https:\/\/content.cloudthat.com\/resources\/wp-content\/uploads\/2022\/11\/cass-1024x249.png\")
<\/a> The owns<\/em> field above indicates the percentage of data owned by each node. As we can see, the owns<\/em> field above is nil as there are no keyspaces\/databases created. So, let us go ahead and create a sample keyspace. We shall create a keyspace with data replication strategy & replication factor. Replication strategy indicates the nodes where replicas are placed. And, the total number of replicas across the cluster is known as replication factor. We shall use NetworkTopology replication strategy since we have our cluster deployed across multiple availability zones. NetworkTopologyStrategy places replicas on distinct racks\/AZs as sometimes, nodes in the same rack\/AZ might usually fail at the same time due to power, cooling or network issues.<\/p>\nLet us set the replication factor to 3 for our \u201cfirst\u201d keyspace:<\/p>\n
CREATE KEYSPACE \"first\" WITH REPLICATION ={'class' :'NetworkTopologyStrategy', 'us-east' : 3};<\/pre>\nThe above CQL command creates a database\/keyspace ‘first’ with class as NetworkTopologyStrategy and 3 replicas in us-east (In this case, one replica in AZ\/rack 1a, one replica in rack AZ\/1b and one replica in rack AZ\/1c). Cassandra uses a command prompt called Cassandra Query Language Shell, also known as CQLSH, which acts as an interface for users to communicate with it. Using CQLSH, you can execute queries using Cassandra Query Language (CQL).<\/p>\n
Next, we shall create a table user<\/em> with 5 records for tests.<\/p>\n
CREATE TABLE user(user_id text,login text,region text,PRIMARY KEY (user_id));<\/pre>\n
Now, let us insert some queries in this table:<\/p>\n
insert into user (user_id,login,region) values ('1','test.1,'IN');\r\ninsert into user (user_id,login,region) values ('2','test.2','IN');\r\ninsert into user (user_id,login,region) values ('3','test.3','IN');\r\ninsert into user (user_id,login,region) values ('4','test.4','IN');\r\ninsert into user (user_id,login,region) values ('5','test.5','IN');<\/pre>\n<\/p>\n
cqlsh> select * from user;<\/pre>\n