Thanks for this.
After doing some more research, I found that xpack was enabled and because of that it did not accept unauthenticated http requests. Once I disabled xpack in the elasticsearch.yml, everything started to work.
admin@zammad:~$ curl -XGET http://127.0.0.1:9200/_cluster/health?pretty
{
"cluster_name" : "elasticsearch",
"status" : "green",
"timed_out" : false,
"number_of_nodes" : 1,
"number_of_data_nodes" : 1,
"active_primary_shards" : 0,
"active_shards" : 0,
"relocating_shards" : 0,
"initializing_shards" : 0,
"unassigned_shards" : 0,
"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" : 100.0
}
Thank you for your help.