Template to set number of shards to 1

single_shard_template.txt

# start with a clean install
DELETE test_index
DELETE _template/my_global_template

#create an index
PUT test_index
GET test_index/_settings

# if ES < 7.0 this will have 5 primary shards

# remove the index
DELETE test_index

# add a global template
PUT _template/my_global_template
{
  "index_patterns": ["*"],
  "settings" : {
        "number_of_shards" : 1
  },
  "order" : 1
}

#re-create the index
PUT test_index
GET test_index/_settings

# new index will have 1 primary shard