Running a single-node cluster and was working great. I had to reboot the server and am now seeing errors regarding "no known master node" and "[SERVICE_UNAVAILABLE/1/state not recovered / initialized]" (see logs below).
Here is my elasticsearch.yml config
# ======================== 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
#
# ---------------------------------- Cluster -----------------------------------
#
# Use a descriptive name for your cluster:
#
#cluster.name: my-application
#
# ------------------------------------ Node ------------------------------------
#
# Use a descriptive name for the node:
#
node.name: node-1
cluster.initial_master_nodes: ["10.0.10.6"]
node.master: true
node.data: true
#
# Add custom attributes to the node:
#
#node.attr.rack: r1
#
# ----------------------------------- 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
#
# ----------------------------------- Memory -----------------------------------
#
# Lock the memory on startup:
#
#bootstrap.memory_lock: true
#
# Make sure that the heap size is set to about half the memory available
# on the system and that the owner of the process is allowed to use this
# limit.
#
# Elasticsearch performs poorly when the system is swapping the memory.
#
# ---------------------------------- Network -----------------------------------
#
# Set the bind address to a specific IP (IPv4 or IPv6):
#
network.host: 10.0.10.6
#
# Set a custom port for HTTP:
#
http.port: 9200
#
# For more information, consult the network module documentation.
#
# --------------------------------- Discovery ----------------------------------
#
# Pass an initial list of hosts to perform discovery when this node is started:
# The default list of hosts is ["127.0.0.1", "[::1]"]
#
#discovery.seed_hosts: ["10.0.10.6"]
#
# Bootstrap the cluster using an initial set of master-eligible nodes:
#
#cluster.initial_master_nodes: ["node-1"]
#
# For more information, consult the discovery and cluster formation module documentation.
#
# ---------------------------------- Gateway -----------------------------------
#
# Block initial recovery after a full cluster restart until N nodes are started:
#
#gateway.recover_after_nodes: 3
#
# For more information, consult the gateway module documentation.
#
# ---------------------------------- Various -----------------------------------
#
# Require explicit names when deleting indices:
#
#action.destructive_requires_name: true
[2019-10-30T12:41:35,226][INFO ][o.e.n.Node ] [node-1] initialized
[2019-10-30T12:41:35,232][INFO ][o.e.n.Node ] [node-1] starting ...
[2019-10-30T12:41:36,582][INFO ][o.e.t.TransportService ] [node-1] publish_address {10.0.10.6:9300}, bound_addresses {10.0.10.6:9300}
[2019-10-30T12:41:37,834][INFO ][o.e.c.c.Coordinator ] [node-1] cluster UUID [YKfRjKvFTlSUuNf6-O9YwA]
[2019-10-30T12:41:38,624][INFO ][o.e.c.s.MasterService ] [node-1] elected-as-master ([1] nodes joined)[{node-1}{6XnZDPQKSOKt6iR66tYEHQ}{9scYkR1XRhOjgQM2lNSxSw}{10.0.10.6}{10.0.10.6:9300}{ml.machine_memory=3587678208, xpack.installed=true, ml.max_open_jobs=20} elect leader, _BECOME_MASTER_TASK_, _FINISH_ELECTION_], term: 2746, version: 5436, reason: master node changed {previous [], current [{node-1}{6XnZDPQKSOKt6iR66tYEHQ}{9scYkR1XRhOjgQM2lNSxSw}{10.0.10.6}{10.0.10.6:9300}{ml.machine_memory=3587678208, xpack.installed=true, ml.max_open_jobs=20}]}
[2019-10-30T12:42:08,053][WARN ][o.e.n.Node ] [node-1] timed out while waiting for initial discovery state - timeout: 30s
[2019-10-30T12:42:08,555][INFO ][o.e.h.AbstractHttpServerTransport] [node-1] publish_address {10.0.10.6:9200}, bound_addresses {10.0.10.6:9200}
[2019-10-30T12:42:08,565][INFO ][o.e.n.Node ] [node-1] started
[2019-10-30T12:42:11,886][DEBUG][o.e.a.a.i.t.g.TransportGetIndexTemplatesAction] [node-1] no known master node, scheduling a retry
[2019-10-30T12:42:11,983][WARN ][r.suppressed ] [node-1] path: /elastalert_status/_search, params: {size=1000, index=elastalert_status}
org.elasticsearch.cluster.block.ClusterBlockException: blocked by: [SERVICE_UNAVAILABLE/1/state not recovered / initialized];
at org.elasticsearch.cluster.block.ClusterBlocks.globalBlockedException(ClusterBlocks.java:189) ~[elasticsearch-7.2.0.jar:7.2.0]