Elasticsearch cluster not success

[Daniel_Chen]

I have two servers both installed Elasticsearch 5.3.0

And with both elasticsearch.yml, I've configed:

cluster.name: alfred
node.name: ${HOSTNAME}
network.host: localhost
discovery.zen.ping.unicast.hosts: ["10.0.6.35", "10.0.6.36"]

after restart both elasticsearch, I ran:

curl -XGET 'localhost:9200/_cluster/health?pretty'

output

{
  "cluster_name" : "alfred",
  "status" : "yellow",
  "timed_out" : false,
  "number_of_nodes" : 1,
  "number_of_data_nodes" : 1,
  "active_primary_shards" : 1,
  "active_shards" : 1,
  "relocating_shards" : 0,
  "initializing_shards" : 0,
  "unassigned_shards" : 1,
  "delayed_unassigned_shards" : 0,
  "number_of_pending_tasks" : 0,
  "number_of_in_flight_fetch" : 0,
  "task_max_waiting_in_queue_millis" : 0,
  "active_shards_percent_as_number" : 50.0
}

why my number_of_nodes still 1? shouldn't it be 2?

curl -X GET 'localhost:9200/_cluster/state?pretty'

output

{
  "cluster_name" : "alfred",
  "version" : 4,
  "state_uuid" : "MsBUYzJDTPiHugbFbtPwVw",
  "master_node" : "WO_y5kdDSbyDCqyhZTcXJQ",
  "blocks" : { },
  "nodes" : {
    "WO_y5kdDSbyDCqyhZTcXJQ" : {
      "name" : "ELK-Node1",
      "ephemeral_id" : "x8TGUy3MS5Cidg3yPy-6oQ",
      "transport_address" : "127.0.0.1:9300",
      "attributes" : { }
    }
  },
  "metadata" : {
...

only one node was listed.

BTW, both server's ufw was inactive.

[Daniel_Chen]

I've figured out the cause of the problem.
in the configuration file, network.host should be the ip address of each node not localhost