Lab 1 – Overview and Setup

In this lab, we’ll bring up a three-node cluster and demonstrate how the WRITE and READ look, in a cluster where our Replication Factor (RF) is set to 3. We’ll simulate a situation where some nodes are down and see how changing the Consistency Level affects the read and write operations and failure conditions in a Scylla cluster.

Before we proceed with the Scylla installation, please ensure that your environment meets the following prerequisites:

1. Docker for Linux, Mac, or Windows. Please note that running in Scylla in Docker is only recommended to evaluate and try Scylla. For best performance, a regular OS install is recommended.
2. 3GB of RAM or greater for Docker
3. If you are using Linux, you will need docker-compose.

 docker run --name Node_X -d scylladb/scylla:4.1.0 

• Create two more nodes, Node_Y and Node_Z, and add them to the cluster of Node_X. The command “$(docker inspect –format='{{ .NetworkSettings.IPAddress }}’ Node_X)” translates to the IP address of Node-X:

docker run --name Node_Y -d scylladb/scylla:4.1.0 --seeds="$(docker inspect --format='{{ .NetworkSettings.IPAddress }}' Node_X)" 
docker run --name Node_Z -d scylladb/scylla:4.1.0 --seeds="$(docker inspect --format='{{ .NetworkSettings.IPAddress }}' Node_X)" 

• Wait a minute or so and check the node status: 

docker exec -it Node_Z nodetool status  

• You’ll see that eventually, all the nodes have UN for status. U means up, and N means normal. Read more about Nodetool Status Here.

Once the nodes are up, and the cluster is set, we can use the CQL shell to create a table.

• Run a CQL shell: 

docker exec -it Node_Z cqlsh 

• Create a keyspace called “mykeyspace”, with a Replication Factor of three: 

CREATE KEYSPACE mykeyspace WITH REPLICATION = { 'class' : 'NetworkTopologyStrategy', 'replication_factor' : 3};

• Next, create a table with three columns: user id, first name, and last name, and insert some data: 

use mykeyspace; 

CREATE TABLE users ( user_id int, fname text, lname text, PRIMARY KEY((user_id))); 

• Insert into the newly created table two rows: 

insert into users(user_id, fname, lname) values (1, 'rick', 'sanchez'); 
insert into users(user_id, fname, lname) values (4, 'rust', 'cohle'); 

• Read the table contents:

select * from users;

To summarize, we saw how to create a three-node cluster with RF=3, how to open a CQL Shell, create a table, insert data into it, and read the data. In the next topic, we will see what happens when nodes are down and how the Consistency Level impacts the read/write operations.