Update ElasticSearch 2.4.3 to 6.x

elasticsearch-upgrade.sh

# on VM
sudo su

rpm --import https://artifacts.elastic.co/GPG-KEY-elasticsearch
touch /etc/yum.repos.d/elasticsearch.repo

echo "[elasticsearch-6.x]
name=Elasticsearch repository for 6.x packages
baseurl=https://artifacts.elastic.co/packages/6.x/yum
gpgcheck=1
gpgkey=https://artifacts.elastic.co/GPG-KEY-elasticsearch
enabled=1
autorefresh=1
type=rpm-md" >> /etc/yum.repos.d/elasticsearch.repo

yum install elasticsearch
# remove old elasticsearch data and directory structure
rm -rf /var/lib/elasticsearch/*
chown -R elasticsearch:elasticsearch /var/lib/elasticsearch
# kill old elastic search process (systemctl won't work since the service should now be pointed at the es6 install)
kill $(cat /var/run/elasticsearch/elasticsearch.pid) && rm /var/run/elasticsearch/elasticsearch.pid
systemctl start elasticsearch.service

# leave sudo
exit

cd /var/www/sites/<project-directory>
bin/magento indexer:reindex catalogsearch_fulltext