Elasticsearch_yaml.sh

####### APPEND TO ELASTICSEARCH CONFIGURATION FILE  ########
echo "node.name: ${node_name}" >> /etc/elasticsearch/elasticsearch.yml
echo "network.host : 0.0.0.0" >> /etc/elasticsearch/elasticsearch.yml
echo "discovery.seed_hosts:" >> /etc/elasticsearch/elasticsearch.yml
echo " - ${elastic_host_1}" >> /etc/elasticsearch/elasticsearch.yml
echo " - ${elastic_host_2}" >> /etc/elasticsearch/elasticsearch.yml
echo " - ${elastic_host_3}" >> /etc/elasticsearch/elasticsearch.yml
echo "cluster.name: elasticsearch" >> /etc/elasticsearch/elasticsearch.yml
echo "cluster.initial_master_nodes:" >> /etc/elasticsearch/elasticsearch.yml
echo " - ${master_node}" >> /etc/elasticsearch/elasticsearch.yml

This file creation is triggered by terraform script? Not sure how and who initiates this file creation.

elasticsearch.yml is created when installing Elasticsearch. These lines are setting the configuration that we need for elasticsearch.
Once we have set all configurations we restart elastic so the config are loaded.