add ElasticSearch notes

etc/elasticsearch/elasticsearch.yml

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+# ======================== Elasticsearch Configuration =========================
+#
+# NOTE: Elasticsearch comes with reasonable defaults for most settings.
+#       Before you set out to tweak and tune the configuration, make sure you
+#       understand what are you trying to accomplish and the consequences.
+#
+# The primary way of configuring a node is via this file. This template lists
+# the most important settings you may want to configure for a production cluster.
+#
+# Please consult the documentation for further information on configuration options:
+# https://www.elastic.co/guide/en/elasticsearch/reference/index.html
+#
+# ----------------------------------- Paths ------------------------------------
+#
+# Path to directory where to store the data (separate multiple locations by comma):
+#
+path.data: /var/lib/elasticsearch
+#
+# Path to log files:
+#
+path.logs: /var/log/elasticsearch
+#
+# ---------------------------------- Network -----------------------------------
+#
+# By default Elasticsearch is only accessible on localhost. Set a different
+# address here to expose this node on the network:
+#
+# network.host: 0.0.0.0
+#
+# By default Elasticsearch listens for HTTP traffic on the first free port it
+# finds starting at 9200. Set a specific HTTP port here:
+#
+http.port: 9200
+#
+# For more information, consult the network module documentation.
+#
+# ---------------------------------- Security ----------------------------------
+#
+#                                 *** WARNING ***
+#
+# Elasticsearch security features are not enabled by default.
+# These features are free, but require configuration changes to enable them.
+# This means that users don’t have to provide credentials and can get full access
+# to the cluster. Network connections are also not encrypted.
+#
+# To protect your data, we strongly encourage you to enable the Elasticsearch security features.
+# Refer to the following documentation for instructions.
+#
+# https://www.elastic.co/guide/en/elasticsearch/reference/7.16/configuring-stack-security.html
+#
+
+# shuts up constant warning logs about security (N/A because of strict firewall):
+xpack.security.enabled: false

etc/elasticsearch/jvm.options.d/heap-size.options

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+-Xms1g
+-Xmx1g