elasticsearch.yml [master node]

    path.data: /var/lib/elasticsearch
    path.logs: /var/log/elasticsearch
    bootstrap.memory_lock: true
    cluster.name: elk.stack
    node.name: aries-n01
    network.host: 10.3.3.30
    http.port: 9200
    node.master: true
    node.data: true
    discovery.zen.ping.unicast.hosts: ["10.3.3.30", "10.3.3.31"]
elasticsearch.yml [data node]

    path.data: /var/lib/elasticsearch
    path.logs: /var/log/elasticsearch
    bootstrap.memory_lock: true
    cluster.name: elk.stack
    node.name: aries-n02
    network.host: 10.3.3.31
    http.port: 9200
    node.master: false
    node.data: true
    discovery.zen.ping.unicast.hosts: ["10.3.3.30", "10.3.3.31"]

kibana.yml [master node]

    server.host: "10.3.3.30"
    elasticsearch.url: "http://10.3.3.30:9200"
kibana.yml [data node]

    server.host: "10.3.3.31"
    elasticsearch.url: "http://10.3.3.31:9200"
logstash.yml [master node]

    path.data: /var/lib/logstash
    path.logs: /var/log/logstash

logstash.yml [data node]

    path.data: /var/lib/logstash
    path.logs: /var/log/logstash
But, above config in 6.7 without any issues. The issue happen after upgrade from 6.7 to 7.0

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