Creating indices based on timestamp using date index name processor

[Daud_Ahmed]

This processor is used to create indices

  {
      "date_index_name": {
        "field": "timestamp",
        "date_rounding": "d",
        "index_name_prefix": "{{fields.index_prefix}}",
        "index_name_format": "yyyy.MM.dd",
        "ignore_failure": false
      }
    },

this create index daily and sets the name rightly using index_name_format ...... what i want to know how can i modify this to create the index monthly....

for testing purpose what i did is i changed the

index_name_format: "yyyy.MM.dd.mm"

it created an index with right format as i was expecting. But i was expecting a new index will be created every minute but it doesn't....