Introduction to Apache Cassandra Apache Cassandra is an open-source, distributed NoSQL database management system designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure

Today's lab session focused on Apache Cassandra! We will install and run the basic commands to containerise and create a cluster of Cassandra NoSQL nodes.

• Configure Cassandra containers on aws ec2
• Run a Cassandra cluster
• Run the basic commands to interact with Cassandra

we will need a ec2 instance. I used the following configuration.

• Machine type: t2-large

• HTTP traffic: On

• HTTPS traffic: On

• Image: ubuntu-20.04

• Size (GB): 30

  Lets start

Let's update our system.

sudo apt-get update

We can now install Docker; make sure you type Y for Yes when prompted.

sudo apt-get install docker.io -y

What is the Docker version? Run the next command

sudo docker --version

Let's create a new user called docker-user. You can use this user to run our containers.

sudo adduser docker-user

We will need to give sudo access to our new docker-user, so let's add it to the sudo group.

sudo usermod -aG sudo docker-user

If we don't add the user in the sudo group, we will not run sudo commands.

Now, run the following command; this will allow us to give sudo permissions to docker to run our commands.

sudo usermod -aG docker docker-user

This command ensures that our new docker-user can run docker commands without using the sudo keyword. For example, instead of running always:

$ sudo docker <command> 

we will be able to run:

$ docker <command>

Let's switch users, type the following command.

su - docker-user

• We should be ready now! Try the following command to see if everything works fine.

docker

• You should be able to see a list of available options and commands. We can always refer to this when we need to explore using commands and options.

Our next step is to create a create a Cassandra container.

• Let us run a new Casandra node using Docker, we can name the new container my-cassandra-1.

docker run --name my-cassandra-1 -m 2g -d cassandra:3.11

The option -m 2g will assign 2GB of memory in this container.

We just created an Apache Cassandra container `my-cassandra-1; let us check the active containers running the following command.

docker ps -a

The container is up and running!

• Let's stop the container and create our first cluster.

docker stop my-cassandra-1 

• Then delete it.

docker rm my-cassandra-1 

We will create a cluster of three Cassandra nodes; the first Cassandra node will be called cassandra-1. we will use Cassandra 3.11.

• We will interact with the cluster using the nodetool.
• The nodetool utility is a command-line interface for managing a Cassandra cluster. The Cassandra cluster will work as one unique database system to manipulate data.

docker run --name cassandra-1 -d cassandra:3.11

Using the docker ps -a command, you can check if your container is up and running.

It is good to check if the container is up and running each time we create one.

• Let us inspect cassandra-1.

docker inspect cassandra-1

The output shows the configuration parameters of our container; if we want to extract a particular value, we can use the following command.

• The command extracts the IPAddress of container cassandra-1

docker inspect --format='{{ .NetworkSettings.IPAddress }}' cassandra-1

# The output is the container IP address
# 172.17.0.2

There are different ways to create a cluster; the most common practice is to set up a cluster configuring the IP addresses of containers or VMs. Since we run everything in the same VM, we can use the container names rather than IPs. * Before we proceed, let's make sure that our container is up and running. It should be up and running as we extracted the IP address.

docker ps -a

Let's use the nodetool command in cassandra-1 to check if our Cassandra node is up and running.

docker exec -i -t cassandra-1 bash -c 'nodetool status'

• The output should look like this:

Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address     Load       Tokens       Owns (effective)  Host ID                               Rack
UN  172.17.0.2  100.22 KiB  256          100.0%            abc2a2ee-9bff-415f-8cd0-f8a19295e846  rack1

• The output shows that our container is in UN status ( Up and Normal) :happy:

Let's connect our second container. Run the following command to create the second Cassandra node cassandra-2.

docker run --name cassandra-2 -d --link cassandra-1:cassandra cassandra:3.11

• We used the --link cassandra1:cassandra option to link cassandra-1 to cassandra-2. This will create our cluster.

Let us check the status of the containers.

docker exec -i -t cassandra-1 bash -c 'nodetool status' 

• The output is:

Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address     Load       Tokens       Owns (effective)  Host ID                               Rack
UJ  172.17.0.3  30.47 KiB  256          ?                 bff8c5c1-8af3-4eb9-bfce-a6f90c049972  rack1
UN  172.17.0.2  70.9 KiB   256          100.0%            abc2a2ee-9bff-415f-8cd0-f8a19295e846  rack1

• If you see a question mark (?) in Owns, that’s fine!
• You noticed that the status is UJ , which means Up and in Join

Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address     Load       Tokens       Owns (effective)  Host ID                               Rack
UN  172.17.0.3  70.92 KiB  256          100.0%            bff8c5c1-8af3-4eb9-bfce-a6f90c049972  rack1
UN  172.17.0.2  75.93 KiB  256          100.0%            abc2a2ee-9bff-415f-8cd0-f8a19295e846  rack1

• Both containers are up and running in normal state (UN) as part of the same datacenter.

Now let's create the third container We can start both containers.

docker start cassandra-1 cassandra-2

Let's run the nodetool command once more.

docker exec -i -t cassandra-1 bash -c 'nodetool status'

• The output shows both containers in UN status.

Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address     Load       Tokens       Owns (effective)  Host ID                            
   Rack
UN  172.17.0.3  137.64 KiB  256          100.0%            624f33b5-10b0-4231-b101-a5a2d07d17
fa  rack1
UN  172.17.0.2  137.47 KiB  256          100.0%            3bba3a8b-c072-4991-93f7-780b3a0071
81  rack1

Let's start the third container

docker run --name cassandra-3 -d --link cassandra-1:cassandra cassandra:3.11

• Let's see the active containers.

docker ps -a 

The output shows three running containers 😄

Then run the nodetool again in cassandra-2.

docker exec -i -t cassandra-2 bash -c 'nodetool status'

We should be able to see our cluster:

Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address     Load       Tokens       Owns (effective)  Host ID                            
   Rack
UN  172.17.0.3  113.1 KiB  256          66.1%             624f33b5-10b0-4231-b101-a5a2d07d17f
a  rack1
UN  172.17.0.2  137.47 KiB  256          66.8%             3bba3a8b-c072-4991-93f7-780b3a0071
81  rack1
UN  172.17.0.4  30.47 KiB  256          67.1%             ce5d8e84-8f62-44e4-a97e-453e55b7ace
a  rack1

• Again, you might need to wait for the status to be UN, so dont worry about the ? in STATUS.
• The gossip protocol runs in all the containers and is responsible for controlling information about our cluster (racks, tokens etc.).
• You can add more nodes in the cluster by running similar commands. Note, that each Cassandra container allocates an amount of computational resources, so you need to monitor if the container fails or not due to insufficient memory or space.

Great! We have a Cassandra cluster up and running!