Number of Replicas is always 1 by default

Elastic Stack Elasticsearch
1

All our indices were "yellow" and we discovered it's because the number of replicas was set to 1. When we update the number of replicas to 0 the indexes are green.

Because we periodically re-create our indices and re-index them we added the following to our index creation:

{
    "index" : {
        "number_of_replicas" : 0
    },
    "mappings": {
        "doc": {
            "properties": {
                ...

However, such indices are still created with number_of_replicas = 1 as is visible in: GET /_cat/indices:

health status index            uuid pri rep docs.count
yellow open   logs-test1       ...   5   1    3316531
  1. Why does ES set 1 by default? Sounds wrong.
  2. Why does ES ignore the 0 when we create the index?
2

It is because the default is always one
as you are only having one instance thats why the status is yellow

3

Why is the default 1? => Because it is 1. OK, that's cleared that up for us.

4

Please show exactly how you create the index.

5 
PUT /logs-test1

{
    "index" : {
        "number_of_replicas" : 0
    },
    "mappings": {
        "doc": {
            "properties": {
                "category": {"type": "keyword"},
                "id": {"type": "long"},
                "subcategory": {"type": "keyword"},
                "timestamp": {"type": "date","format": "date_time||epoch_millis"},
                "type": {"type": "keyword"}
            }
        }
    }
}
6

You are missing the settings level, which is why your settings are not recognised:

PUT /logs-test1
{
  "settings": {
    "index" : {
      "number_of_replicas" : 0
    }
  },
  "mappings": {
    "doc": {
      "properties": {
        "category": {"type": "keyword"},
        "id": {"type": "long"},
        "subcategory": {"type": "keyword"},
        "timestamp": {"type": "date","format": "date_time||epoch_millis"},
        "type": {"type": "keyword"}
      }
    }
  }
}
7

Thanks muchly!