Master not discovered yet, this node has not previously joined a bootstrapped (v7+) cluster

ES V7.9.0
I had used ES V7.6.0 with default configuration, but in V7.9.0 I am facing above mentioned issue.
I looked into output of both the versions and found that V7.6.0 was able to generate "cluster_uuid" : "7PaoDBXySHa3djdAUOTYPw", by default without doing any configuration changes, whereas in case of V7.9.0 it was generating it like "cluster_uuid" : "na", I am not sure whether this is causing above mentioned error or not.

What are your elasticsearch.yml settings for the nodes, as not sure what you mean by default config as you need to set the IP at least?

I'd think UUID of n'a means this node is not a master and thus looking for masters, so need to see the configs and also are you on Docker, etc.

  1. elasticserch.yml for each node
  2. Docker or containers?
  3. Architecture, i.e. how many masters, data, etc. nodes

======================== 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

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: /path/to/data

Path to log files:

#path.logs: /path/to/logs

----------------------------------- 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: 192.168.0.1
network.host: site

Set a custom port for HTTP:

#http.port: 9200
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: ["host1", "host2"]
discovery.seed_hosts: ["MyMachineName"]

Bootstrap the cluster using an initial set of master-eligible nodes:

#cluster.initial_master_nodes: ["node-1", "node-2"]

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
xpack.ml.enabled: false