ElasticSearch

1. Install Elasticsearch 5.6:
   1. sudo apt install openjdk-8-jre-headless
   2. Follow the instructions at https://www.elastic.co/guide/en/elasticsearch/reference/current/deb.html making sure to substitute the version numbers with 5.6
   3. Follow the instructions at https://www.elastic.co/guide/en/elasticsearch/reference/current/deb.html#deb-running-systemd
2. Configure it to use 1GB heap size (by default, it’s 2GB). This will help minimise memory issues:
   
   # nano /etc/elasticsearch/jvm.options
   -Xms1g
   -Xmx1g
   
3. Install custom script to restart elastic search when it’s down. Then add it as a cron job to run every minute:
   
   # ~/superviseElasticSearch.sh
   PATH=/usr/sbin:/usr/bin:/sbin:/bin
   ps -ef | grep elasticsearch | grep -v grep
   if [ ! $? -eq "0" ]; then
   service elasticsearch start
   fi
   
   #crontab -e
   * * * * * bash ~/superviseElasticSearch.sh