OpenSearch/docs/reference/api-conventions.asciidoc

[[api-conventions]]
== API conventions

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>>
* <<cron-expressions>>
* <<common-options>>
* <<url-access-control>>

[[multi-index]]
=== Multi-target syntax

Most APIs that accept a `<data-stream>`, `<index>`, or `<target>` request path
parameter also support _multi-target syntax_.

In multi-target syntax, you can use a comma-separated list to run a request on
multiple resources, such as data streams, indices, or index aliases:
`test1,test2,test3`. You can also use {wikipedia}/Glob_(programming)[glob-like]
wildcard (`*`) expressions to target resources that match a pattern: `test*` or
`*test` or `te*t` or `*test*`.

You can exclude targets using the `-` character: `test*,-test3`.

IMPORTANT: Index aliases are resolved after wildcard expressions. This can
result in a request that targets an excluded alias. For example, if `test3` is
an index alias, the pattern `test*,-test3` still targets the indices for
`test3`. To avoid this, exclude the concrete indices for the alias instead.

Multi-target APIs that can target indices support the following query
string parameters:

include::{es-repo-dir}/rest-api/common-parms.asciidoc[tag=index-ignore-unavailable]

include::{es-repo-dir}/rest-api/common-parms.asciidoc[tag=allow-no-indices]

include::{es-repo-dir}/rest-api/common-parms.asciidoc[tag=expand-wildcards]

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

Some multi-target APIs that can target indices also support the following query
string parameter:

include::{es-repo-dir}/rest-api/common-parms.asciidoc[tag=ignore_throttled]

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

[[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`. Format should be compatible with java-time https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html
`time_zone`:: is the optional time zone. Defaults to `utc`.

NOTE: Pay attention to the usage of small vs capital letters used in the `date_format`. For example:
`mm` denotes minute of hour, while `MM` denotes month of year. Similarly `hh` denotes the hour in the
`1-12` range in combination with `AM/PM`, while `HH` denotes the hour in the `0-23` 24-hour range.

Date math expressions are resolved locale-independent. Consequently, it is not possible to use any other
calendars than the Gregorian calendar.

You must enclose date math index name expressions within angle brackets, and
all special characters should be URI encoded. For example:

[source,console]
----
# PUT /<my-index-{now/d}>
PUT /%3Cmy-index-%7Bnow%2Fd%7D%3E
----

[NOTE]
.Percent encoding of date math characters
======================================================
The special characters used for date rounding must be URI encoded as follows:

[horizontal]
`<`:: `%3C`
`>`:: `%3E`
`/`:: `%2F`
`{`:: `%7B`
`}`:: `%7D`
`|`:: `%7C`
`+`:: `%2B`
`:`:: `%3A`
`,`:: `%2C`
======================================================

The following example shows different forms of date math index names and the final index names
they resolve to given the current time is 22nd 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,console]
----------------------------------------------------------------------
# GET /<logstash-{now/d-2d}>,<logstash-{now/d-1d}>,<logstash-{now/d}>/_search
GET /%3Clogstash-%7Bnow%2Fd-2d%7D%3E%2C%3Clogstash-%7Bnow%2Fd-1d%7D%3E%2C%3Clogstash-%7Bnow%2Fd%7D%3E/_search
{
  "query" : {
    "match": {
      "test": "data"
    }
  }
}
----------------------------------------------------------------------
// TEST[s/^/PUT logstash-2016.09.20\nPUT logstash-2016.09.19\nPUT logstash-2016.09.18\n/]
// TEST[s/now/2016.09.20%7C%7C/]

include::rest-api/cron-expressions.asciidoc[]

[[common-options]]
=== Common options

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

[discrete]
==== 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.


[discrete]
==== Human readable output

Statistics are returned in a format suitable for humans
(e.g. `"exists_time": "1h"` or `"size": "1kb"`) and for computers
(e.g. `"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]]
[discrete]
==== Date Math

Most parameters which accept a formatted date value -- such as `gt` and `lt`
in <<query-dsl-range-query,`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 differ from those supported by <<time-units, time units>> for durations.
The supported units are:

[horizontal]
`y`:: Years
`M`:: Months
`w`:: Weeks
`d`:: Days
`h`:: Hours
`H`:: Hours
`m`:: Minutes
`s`:: Seconds

Assuming `now` is `2001-01-01 12:00:00`, some examples are:

[horizontal]
`now+1h`:: `now` in milliseconds plus one hour. Resolves to: `2001-01-01 13:00:00`
`now-1h`:: `now` in milliseconds minus one hour. Resolves to: `2001-01-01 11:00:00`
`now-1h/d`:: `now` in milliseconds minus one hour, rounded down to UTC 00:00. Resolves to: `2001-01-01 00:00:00`
 `2001.02.01\|\|+1M/d`:: `2001-02-01` in milliseconds plus one month. Resolves to: `2001-03-01 00:00:00`

[discrete]
[[common-options-response-filtering]]
==== 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,console]
--------------------------------------------------
GET /_search?q=kimchy&filter_path=took,hits.hits._id,hits.hits._score
--------------------------------------------------
// TEST[setup:my_index]

Responds:

[source,console-result]
--------------------------------------------------
{
  "took" : 3,
  "hits" : {
    "hits" : [
      {
        "_id" : "0",
        "_score" : 1.6375021
      }
    ]
  }
}
--------------------------------------------------
// TESTRESPONSE[s/"took" : 3/"took" : $body.took/]
// TESTRESPONSE[s/1.6375021/$body.hits.hits.0._score/]

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

[source,console]
--------------------------------------------------
GET /_cluster/state?filter_path=metadata.indices.*.stat*
--------------------------------------------------
// TEST[s/^/PUT my-index-000001\n/]

Responds:

[source,console-result]
--------------------------------------------------
{
  "metadata" : {
    "indices" : {
      "my-index-000001": {"state": "open"}
    }
  }
}
--------------------------------------------------

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,console]
--------------------------------------------------
GET /_cluster/state?filter_path=routing_table.indices.**.state
--------------------------------------------------
// TEST[s/^/PUT my-index-000001\n/]

Responds:

[source,console-result]
--------------------------------------------------
{
  "routing_table": {
    "indices": {
      "my-index-000001": {
        "shards": {
          "0": [{"state": "STARTED"}, {"state": "UNASSIGNED"}]
        }
      }
    }
  }
}
--------------------------------------------------

It is also possible to exclude one or more fields by prefixing the filter with the char `-`:

[source,console]
--------------------------------------------------
GET /_count?filter_path=-_shards
--------------------------------------------------
// TEST[setup:my_index]

Responds:

[source,console-result]
--------------------------------------------------
{
  "count" : 5
}
--------------------------------------------------

And for more control, both inclusive and exclusive filters can be combined in the same expression. In
this case, the exclusive filters will be applied first and the result will be filtered again using the
inclusive filters:

[source,console]
--------------------------------------------------
GET /_cluster/state?filter_path=metadata.indices.*.state,-metadata.indices.logstash-*
--------------------------------------------------
// TEST[s/^/PUT my-index-000001\nPUT my-index-000002\nPUT my-index-000003\nPUT logstash-2016.01\n/]

Responds:

[source,console-result]
--------------------------------------------------
{
  "metadata" : {
    "indices" : {
      "my-index-000001" : {"state" : "open"},
      "my-index-000002" : {"state" : "open"},
      "my-index-000003" : {"state" : "open"}
    }
  }
}
--------------------------------------------------

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,console]
--------------------------------------------------
POST /library/book?refresh
{"title": "Book #1", "rating": 200.1}
POST /library/book?refresh
{"title": "Book #2", "rating": 1.7}
POST /library/book?refresh
{"title": "Book #3", "rating": 0.1}
GET /_search?filter_path=hits.hits._source&_source=title&sort=rating:desc
--------------------------------------------------

[source,console-result]
--------------------------------------------------
{
  "hits" : {
    "hits" : [ {
      "_source":{"title":"Book #1"}
    }, {
      "_source":{"title":"Book #2"}
    }, {
      "_source":{"title":"Book #3"}
    } ]
  }
}
--------------------------------------------------


[discrete]
==== Flat Settings

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

[source,console]
--------------------------------------------------
GET my-index-000001/_settings?flat_settings=true
--------------------------------------------------
// TEST[setup:my_index]

Returns:

[source,console-result]
--------------------------------------------------
{
  "my-index-000001" : {
    "settings": {
      "index.number_of_replicas": "1",
      "index.number_of_shards": "1",
      "index.creation_date": "1474389951325",
      "index.uuid": "n6gzFZTgS664GUfx0Xrpjw",
      "index.version.created": ...,
      "index.routing.allocation.include._tier" : "data_content",
      "index.provided_name" : "my-index-000001"
    }
  }
}
--------------------------------------------------
// TESTRESPONSE[s/1474389951325/$body.my-index-000001.settings.index\\\\.creation_date/]
// TESTRESPONSE[s/n6gzFZTgS664GUfx0Xrpjw/$body.my-index-000001.settings.index\\\\.uuid/]
// TESTRESPONSE[s/"index.version.created": \.\.\./"index.version.created": $body.my-index-000001.settings.index\\\\.version\\\\.created/]

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

[source,console]
--------------------------------------------------
GET my-index-000001/_settings?flat_settings=false
--------------------------------------------------
// TEST[setup:my_index]

Returns:

[source,console-result]
--------------------------------------------------
{
  "my-index-000001" : {
    "settings" : {
      "index" : {
        "number_of_replicas": "1",
        "number_of_shards": "1",
        "creation_date": "1474389951325",
        "uuid": "n6gzFZTgS664GUfx0Xrpjw",
        "version": {
          "created": ...
        },
        "routing": {
          "allocation": {
            "include": {
              "_tier": "data_content"
            }
          }
        },
        "provided_name" : "my-index-000001"
      }
    }
  }
}
--------------------------------------------------
// TESTRESPONSE[s/1474389951325/$body.my-index-000001.settings.index.creation_date/]
// TESTRESPONSE[s/n6gzFZTgS664GUfx0Xrpjw/$body.my-index-000001.settings.index.uuid/]
// TESTRESPONSE[s/"created": \.\.\./"created": $body.my-index-000001.settings.index.version.created/]

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

[discrete]
==== Parameters

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

[discrete]
==== Boolean Values

All REST API parameters (both request parameters and JSON body) support
providing boolean "false" as the value `false` and boolean "true" as the
value `true`. All other values will raise an error.

[discrete]
==== Number Values

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

[[time-units]]
[discrete]
==== Time units

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

[horizontal]
`d`::       Days
`h`::       Hours
`m`::       Minutes
`s`::       Seconds
`ms`::      Milliseconds
`micros`::  Microseconds
`nanos`::   Nanoseconds

[[byte-units]]
[discrete]
==== Byte size units

Whenever the byte size of data needs to be specified, e.g. when setting a buffer size
parameter, the value must specify the unit, like `10kb` for 10 kilobytes. Note that
these units use powers of 1024, so `1kb` means 1024 bytes. The supported units are:

[horizontal]
`b`::   Bytes
`kb`::  Kilobytes
`mb`::  Megabytes
`gb`::  Gigabytes
`tb`::  Terabytes
`pb`::  Petabytes

[[size-units]]
[discrete]
==== Unit-less quantities

Unit-less quantities means that they don't have a "unit" like "bytes" or "Hertz" or "meter" or "long tonne".

If one of these quantities is large we'll print it out like 10m for 10,000,000 or 7k for 7,000. We'll still print 87
when we mean 87 though. These are the supported multipliers:

[horizontal]
`k`::  Kilo
`m`::  Mega
`g`::  Giga
`t`::  Tera
`p`::  Peta

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

Wherever distances need to be specified, such as the `distance` parameter in
the <<query-dsl-geo-distance-query>>), the default unit is meters if none is specified.
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`

[[fuzziness]]
[discrete]
==== Fuzziness

Some queries and APIs support parameters to allow inexact _fuzzy_ matching,
using the `fuzziness` parameter.

When querying `text` or `keyword` fields, `fuzziness` is interpreted as a
{wikipedia}/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:

[horizontal]
`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.
Low and high distance arguments may be optionally provided `AUTO:[low],[high]`. If not specified,
the default values are 3 and 6, equivalent to `AUTO:3,6` that make 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`.
--

[discrete]
[[common-options-error-options]]
==== Enabling stack traces

By default when a request returns an error Elasticsearch doesn't include the
stack trace of the error. You can enable that behavior by setting the
`error_trace` url parameter to `true`. For example, by default when you send an
invalid `size` parameter to the `_search` API:

[source,console]
----------------------------------------------------------------------
POST /my-index-000001/_search?size=surprise_me
----------------------------------------------------------------------
// TEST[s/surprise_me/surprise_me&error_trace=false/ catch:bad_request]
// Since the test system sends error_trace=true by default we have to override

The response looks like:

[source,console-result]
----------------------------------------------------------------------
{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "Failed to parse int parameter [size] with value [surprise_me]"
      }
    ],
    "type" : "illegal_argument_exception",
    "reason" : "Failed to parse int parameter [size] with value [surprise_me]",
    "caused_by" : {
      "type" : "number_format_exception",
      "reason" : "For input string: \"surprise_me\""
    }
  },
  "status" : 400
}
----------------------------------------------------------------------

But if you set `error_trace=true`:

[source,console]
----------------------------------------------------------------------
POST /my-index-000001/_search?size=surprise_me&error_trace=true
----------------------------------------------------------------------
// TEST[catch:bad_request]

The response looks like:

[source,console-result]
----------------------------------------------------------------------
{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "Failed to parse int parameter [size] with value [surprise_me]",
        "stack_trace": "Failed to parse int parameter [size] with value [surprise_me]]; nested: IllegalArgumentException..."
      }
    ],
    "type": "illegal_argument_exception",
    "reason": "Failed to parse int parameter [size] with value [surprise_me]",
    "stack_trace": "java.lang.IllegalArgumentException: Failed to parse int parameter [size] with value [surprise_me]\n    at org.elasticsearch.rest.RestRequest.paramAsInt(RestRequest.java:175)...",
    "caused_by": {
      "type": "number_format_exception",
      "reason": "For input string: \"surprise_me\"",
      "stack_trace": "java.lang.NumberFormatException: For input string: \"surprise_me\"\n    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)..."
    }
  },
  "status": 400
}
----------------------------------------------------------------------
// TESTRESPONSE[s/"stack_trace": "Failed to parse int parameter.+\.\.\."/"stack_trace": $body.error.root_cause.0.stack_trace/]
// TESTRESPONSE[s/"stack_trace": "java.lang.IllegalArgum.+\.\.\."/"stack_trace": $body.error.stack_trace/]
// TESTRESPONSE[s/"stack_trace": "java.lang.Number.+\.\.\."/"stack_trace": $body.error.caused_by.stack_trace/]

[discrete]
==== 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. When using this method, the `source_content_type` parameter
should also be passed with a media type value that indicates the format
of the source, such as `application/json`.

[discrete]
==== Content-Type Requirements

The type of the content sent in a request body must be specified using
the `Content-Type` header. The value of this header must map to one of
the supported formats that the API supports. Most APIs support JSON,
YAML, CBOR, and SMILE. The bulk and multi-search APIs support NDJSON,
JSON, and SMILE; other types will result in an error response.

Additionally, when using the `source` query string parameter, the
content type must be specified using the `source_content_type` query
string parameter.

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

Many users use a proxy with URL-based access control to secure access to
{es} data streams and indices. For <<search-multi-search,multi-search>>,
<<docs-multi-get,multi-get>>, and <<docs-bulk,bulk>> requests, the user has
the choice of specifying a data stream or  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 data stream or index specified in the
URL, set `rest.action.multi.allow_explicit_index` to `false` in `elasticsearch.yml`.


This causes  {es} to
reject requests that explicitly specify a data stream or index in the request body.