Install Datastax PHP Driver

sudo apt-add-repository ppa:ondrej/php
sudo apt update
sudo apt install apache2 php7.1 php7.1-xml php7.1-dev libgmp-dev libpcre3-dev g++ make cmake libssl-dev openssl

sudo systemctl status apache2

wget https://downloads.datastax.com/cpp-driver/ubuntu/18.04/dependencies/libuv/v1.35.0/libuv1_1.35.0-1_amd64.deb
wget https://downloads.datastax.com/cpp-driver/ubuntu/18.04/dependencies/libuv/v1.35.0/libuv1-dev_1.35.0-1_amd64.deb
wget http://security.ubuntu.com/ubuntu/pool/main/g/glibc/multiarch-support_2.27-3ubuntu1.2_amd64.deb
wget https://downloads.datastax.com/cpp-driver/ubuntu/18.04/cassandra/v2.15.3/cassandra-cpp-driver_2.15.3-1_amd64.deb
wget https://downloads.datastax.com/cpp-driver/ubuntu/18.04/cassandra/v2.15.3/cassandra-cpp-driver-dev_2.15.3-1_amd64.deb

sudo dpkg -i multiarch-support_2.27-3ubuntu1.2_amd64.deb
sudo dpkg -i cassandra-cpp-driver_2.15.3-1_amd64.deb
sudo dpkg -i cassandra-cpp-driver-dev_2.15.3-1_amd64.deb
sudo dpkg -i libuv1_1.35.0-1_amd64.deb
sudo dpkg -i libuv1-dev_1.35.0-1_amd64.deb

sudo pecl install cassandra

sudo nano /etc/php/7.1/apache2/php.ini
NOTE: Ctrl+W, search for "Dynamic Extensions"
NOTE: add extension=cassandra.so to end of dynamic extensions section

sudo service apache2 restart