A WIP not fully vetted out yet, but should get you most of the way there

Cassandra Ubuntu EC2 setup script

sudo apt update
sudo apt dist-upgrade -y
sudo apt install -y vim-tiny openjdk-8-jre-headless
curl https://www.apache.org/dist/cassandra/KEYS | sudo apt-key add -
sudo apt-key adv --keyserver pool.sks-keyservers.net --recv-key A278B781FE4B2BDA
echo "deb http://www.apache.org/dist/cassandra/debian 22x main" | sudo tee -a /etc/apt/sources.list.d/cassandra.sources.list
echo "deb-src http://www.apache.org/dist/cassandra/debian 22x main" | sudo tee -a /etc/apt/sources.list.d/cassandra.sources.list
gpg --keyserver pgp.mit.edu --recv-keys F758CE318D77295D
gpg --export --armor F758CE318D77295D | sudo apt-key add -
gpg --keyserver pgp.mit.edu --recv-keys 2B5C1B00
gpg --export --armor 2B5C1B00 | sudo apt-key add -
gpg --keyserver pgp.mit.edu --recv-keys 0353B12C
gpg --export --armor 0353B12C | sudo apt-key add -
sudo apt-get update
sudo apt-get install cassandra
sudo systemctl start cassandra.service
sudo reboot

# Then go into the cassandra.yaml file and set these settings for a single node configuration:
# listen_address: 127.0.0.1
# rpc_address: 0.0.0.0
# broadcast_rpc_address: <your ec2 private ip address>
# endpoint_snitch: SimpleSnitch