OpenSearch/docs/reference/api-conventions.asciidoc

[[api-conventions]]
= API Conventions

[partintro]
--
The *elasticsearch* REST APIs are exposed using <<modules-http,JSON over HTTP>>.

The conventions listed in this chapter can be applied throughout the REST
API, unless otherwise specified.

* <<multi-index>>
* <<date-math-index-names>>
* <<common-options>>

--

[[multi-index]]
== Multiple Indices

Most APIs that refer to an `index` parameter support execution across multiple indices,
using simple `test1,test2,test3` notation (or `_all` for all indices). It also
support wildcards, for example: `test*`, and the ability to "add" (`+`)
and "remove" (`-`), for example: `+test*,-test3`.

All multi indices API support the following url query string parameters:

`ignore_unavailable`::

Controls whether to ignore if any specified indices are unavailable, this
includes indices that don't exist or closed indices. Either `true` or `false`
can be specified.

`allow_no_indices`::

Controls whether to fail if a wildcard indices expressions results into no
concrete indices. Either `true` or `false` can be specified. For example if
the wildcard expression `foo*` is specified and no indices are available that
start with `foo` then depending on this setting the request will fail. This
setting is also applicable when `_all`, `*` or no index has been specified. This
settings also applies for aliases, in case an alias points to a closed index.

`expand_wildcards`::

Controls to what kind of concrete indices wildcard indices expression expand
to. If `open` is specified then the wildcard expression is expanded to only
open indices and if `closed` is specified then the wildcard expression is
expanded only to closed indices. Also both values (`open,closed`) can be
specified to expand to all indices.

If `none` is specified then wildcard expansion will be disabled and if `all`
is specified, wildcard expressions will expand to all indices (this is equivalent
to specifying `open,closed`).

The defaults settings for the above parameters depend on the api being used.

NOTE: Single index APIs such as the <<docs>> and the
<<indices-aliases,single-index `alias` APIs>> do not support multiple indices.

[[date-math-index-names]]
== Date math support in index names

Date math index name resolution enables you to search a range of time-series indices, rather
than searching all of your time-series indices and filtering the results or maintaining aliases.
Limiting the number of indices that are searched reduces the load on the cluster and improves
execution performance. For example, if you are searching for errors in your
daily logs, you can use a date math name template to restrict the search to the past
two days.

Almost all APIs that have an `index` parameter, support date math in the `index` parameter
value.

A date math index name takes the following form:

[source,txt]
----------------------------------------------------------------------
<static_name{date_math_expr{date_format|time_zone}}>
----------------------------------------------------------------------

Where:

[horizontal]
`static_name`:: is the static text part of the name
`date_math_expr`:: is a dynamic date math expression that computes the date dynamically
`date_format`:: is the optional format in which the computed date should be rendered. Defaults to `YYYY.MM.dd`.
`time_zone`:: is the optional time zone . Defaults to `utc`.

You must enclose date math index name expressions within angle brackets. For example:

[source,js]
----------------------------------------------------------------------
curl -XGET 'localhost:9200/<logstash-{now/d-2d}>/_search' {
  "query" : {
    ...
  }
}
----------------------------------------------------------------------

The following example shows different forms of date math index names and the final index names
they resolve to given the current time is 22rd March 2024 noon utc.

[options="header"]
|======
| Expression                		      |Resolves to
| `<logstash-{now/d}>`      		      | `logstash-2024.03.22`
| `<logstash-{now/M}>`      		      | `logstash-2024.03.01`
| `<logstash-{now/M{YYYY.MM}}>`           | `logstash-2024.03`
| `<logstash-{now/M-1M{YYYY.MM}}>`        | `logstash-2024.02`
| `<logstash-{now/d{YYYY.MM.dd\|+12:00}}`  | `logstash-2024.03.23`
|======

To use the characters `{` and `}` in the static part of an index name template, escape them
with a backslash `\`, for example:

 * `<elastic\\{ON\\}-{now/M}>` resolves to `elastic{ON}-2024.03.01`

The following example shows a search request that searches the Logstash indices for the past
three days, assuming the indices use the default Logstash index name format,
`logstash-YYYY.MM.dd`.

[source,js]
----------------------------------------------------------------------
curl -XGET 'localhost:9200/<logstash-{now/d-2d}>,<logstash-{now/d-1d}>,<logstash-{now/d}>/_search' {
  "query" : {
    ...
  }
}
----------------------------------------------------------------------

[[common-options]]
== Common options

The following options can be applied to all of the REST APIs.

[float]
=== Pretty Results

When appending `?pretty=true` to any request made, the JSON returned
will be pretty formatted (use it for debugging only!). Another option is
to set `?format=yaml` which will cause the result to be returned in the
(sometimes) more readable yaml format.


[float]
=== Human readable output

Statistics are returned in a format suitable for humans
(eg `"exists_time": "1h"` or `"size": "1kb"`) and for computers
(eg `"exists_time_in_millis": 3600000` or `"size_in_bytes": 1024`).
The human readable values can be turned off by adding `?human=false`
to the query string. This makes sense when the stats results are
being consumed by a monitoring tool, rather than intended for human
consumption.  The default for the `human` flag is
`false`.

[[date-math]]
[float]
=== Date Math

Most parameters which accept a formatted date value -- such as `gt` and `lt`
in <<query-dsl-range-query,range queries>> `range` queries, or `from` and `to`
in <<search-aggregations-bucket-daterange-aggregation,`daterange`
aggregations>> -- understand date maths.

The expression starts with an anchor date, which can either be `now`, or a
date string ending with `||`. This anchor date can optionally be followed by
one or more maths expressions:

* `+1h` - add one hour
* `-1d` - subtract one day
* `/d`  - round down to the nearest day

The supported <<time-units,time units>> are: `y` (year), `M` (month), `w` (week),
`d` (day), `h` (hour), `m` (minute), and `s` (second).

Some examples are:

[horizontal]
`now+1h`::              The current time plus one hour, with ms resolution.
`now+1h+1m`::           The current time plus one hour plus one minute, with ms resolution.
`now+1h/d`::            The current time plus one hour, rounded down to the nearest day.
`2015-01-01||+1M/d`::   `2015-01-01` plus one month, rounded down to the nearest day.

[float]
=== Response Filtering

All REST APIs accept a `filter_path` parameter that can be used to reduce
the response returned by elasticsearch. This parameter takes a comma
separated list of filters expressed with the dot notation:

[source,sh]
--------------------------------------------------
curl -XGET 'localhost:9200/_search?pretty&filter_path=took,hits.hits._id,hits.hits._score'
{
  "took" : 3,
  "hits" : {
    "hits" : [
      {
        "_id" : "3640",
        "_score" : 1.0
      },
      {
        "_id" : "3642",
        "_score" : 1.0
      }
    ]
  }
}
--------------------------------------------------

It also supports the `*` wildcard character to match any field or part
of a field's name:

[source,sh]
--------------------------------------------------
curl -XGET 'localhost:9200/_nodes/stats?filter_path=nodes.*.ho*'
{
  "nodes" : {
    "lvJHed8uQQu4brS-SXKsNA" : {
      "host" : "portable"
    }
  }
}
--------------------------------------------------

And the `**` wildcard can be used to include fields without knowing the
exact path of the field. For example, we can return the Lucene version
of every segment with this request:

[source,sh]
--------------------------------------------------
curl 'localhost:9200/_segments?pretty&filter_path=indices.**.version'
{
  "indices" : {
    "movies" : {
      "shards" : {
        "0" : [ {
          "segments" : {
            "_0" : {
              "version" : "5.2.0"
            }
          }
        } ],
        "2" : [ {
          "segments" : {
            "_0" : {
              "version" : "5.2.0"
            }
          }
        } ]
      }
    },
    "books" : {
      "shards" : {
        "0" : [ {
          "segments" : {
            "_0" : {
              "version" : "5.2.0"
            }
          }
        } ]
      }
    }
  }
}
--------------------------------------------------

Note that elasticsearch sometimes returns directly the raw value of a field,
like the `_source` field. If you want to filter `_source` fields, you should
consider combining the already existing `_source` parameter (see
<<get-source-filtering,Get API>> for more details) with the `filter_path`
parameter like this:

[source,sh]
--------------------------------------------------
curl -XGET 'localhost:9200/_search?pretty&filter_path=hits.hits._source&_source=title'
{
  "hits" : {
    "hits" : [ {
      "_source":{"title":"Book #2"}
    }, {
      "_source":{"title":"Book #1"}
    }, {
      "_source":{"title":"Book #3"}
    } ]
  }
}
--------------------------------------------------


[float]
=== Flat Settings

The `flat_settings` flag affects rendering of the lists of settings. When
`flat_settings` flag is `true` settings are returned in a flat format:

[source,js]
--------------------------------------------------
{
  "persistent" : { },
  "transient" : {
    "discovery.zen.minimum_master_nodes" : "1"
  }
}
--------------------------------------------------

When the `flat_settings` flag is `false` settings are returned in a more
human readable structured format:

[source,js]
--------------------------------------------------
{
  "persistent" : { },
  "transient" : {
    "discovery" : {
      "zen" : {
        "minimum_master_nodes" : "1"
      }
    }
  }
}
--------------------------------------------------

By default the `flat_settings` is set to `false`.

[float]
=== Parameters

Rest parameters (when using HTTP, map to HTTP URL parameters) follow the
convention of using underscore casing.

[float]
=== Boolean Values

All REST APIs parameters (both request parameters and JSON body) support
providing boolean "false" as the values: `false`, `0`, `no` and `off`.
All other values are considered "true". Note, this is not related to
fields within a document indexed treated as boolean fields.

[float]
=== Number Values

All REST APIs support providing numbered parameters as `string` on top
of supporting the native JSON number types.

[[time-units]]
[float]
=== Time units

Whenever durations need to be specified, eg for a `timeout` parameter, the
duration must specify the unit, like `2d` for 2 days.  The supported units
are:

[horizontal]
`y`::   Year
`M`::   Month
`w`::   Week
`d`::   Day
`h`::   Hour
`m`::   Minute
`s`::   Second
`ms`::  Milli-second

[[distance-units]]
[float]
=== Distance Units

Wherever distances need to be specified, such as the `distance` parameter in
the <<query-dsl-geo-distance-query>>), the default unit if none is specified is
the meter. Distances can be specified in other units, such as `"1km"` or
`"2mi"` (2 miles).

The full list of units is listed below:

[horizontal]
Mile::          `mi` or `miles`
Yard::          `yd` or `yards`
Feet::          `ft` or `feet`
Inch::          `in` or `inch`
Kilometer::     `km` or `kilometers`
Meter::         `m` or `meters`
Centimeter::    `cm` or `centimeters`
Millimeter::    `mm` or `millimeters`
Nautical mile:: `NM`, `nmi` or `nauticalmiles`

The `precision` parameter in the <<query-dsl-geohash-cell-query>> accepts
distances with the above units, but if no unit is specified, then the
precision is interpreted as the length of the geohash.

[[fuzziness]]
[float]
=== Fuzziness

Some queries and APIs support parameters to allow inexact _fuzzy_ matching,
using the `fuzziness` parameter. The `fuzziness` parameter is context
sensitive which means that it depends on the type of the field being queried:

[float]
==== Numeric, date and IPv4 fields

When querying numeric, date and IPv4 fields, `fuzziness` is interpreted as a
`+/-` margin. It behaves like a <<query-dsl-range-query>> where:

    -fuzziness <= field value <= +fuzziness

The `fuzziness` parameter should be set to a numeric value, eg `2` or `2.0`. A
`date` field interprets a long as milliseconds, but also accepts a string
containing a time value -- `"1h"` -- as explained in <<time-units>>. An `ip`
field accepts a long or another IPv4 address (which will be converted into a
long).

[float]
==== String fields

When querying `string` fields, `fuzziness` is interpreted as a
http://en.wikipedia.org/wiki/Levenshtein_distance[Levenshtein Edit Distance]
-- the number of one character changes that need to be made to one string to
make it the same as another string.

The `fuzziness` parameter can be specified as:

`0`, `1`, `2`::

the maximum allowed Levenshtein Edit Distance (or number of edits)

`AUTO`::
+
--
generates an edit distance based on the length of the term. For lengths:

`0..2`:: must match exactly
`3..5`:: one edit allowed
`>5`:: two edits allowed

`AUTO` should generally be the preferred value for `fuzziness`.
--

[float]
=== Result Casing

All REST APIs accept the `case` parameter. When set to `camelCase`, all
field names in the result will be returned in camel casing, otherwise,
underscore casing will be used. Note, this does not apply to the source
document indexed.

[float]
=== Request body in query string

For libraries that don't accept a request body for non-POST requests,
you can pass the request body as the `source` query string parameter
instead.

[[url-access-control]]
== URL-based access control

Many users use a proxy with URL-based access control to secure access to
Elasticsearch indices. For <<search-multi-search,multi-search>>,
<<docs-multi-get,multi-get>> and <<docs-bulk,bulk>> requests, the user has
the choice of specifying an index in the URL and on each individual request
within the request body. This can make URL-based access control challenging.

To prevent the user from overriding the index which has been specified in the
URL, add this setting to the `config.yml` file:

    rest.action.multi.allow_explicit_index: false

The default value is `true`, but when set to `false`, Elasticsearch will
reject requests that have an explicit index specified in the request body.