[DOCS] Add get index alias API docs (#46046)

docs/reference/indices.asciidoc

@@ -34,6 +34,7 @@ index settings, aliases, mappings, and index templates.
 [float]
 [[alias-management]]
 === Alias management:
+* <<indices-get-alias>>
 * <<indices-alias-exists>>
 * <<indices-aliases>>
 
@@ -93,6 +94,8 @@ include::indices/get-field-mapping.asciidoc[]
 
 include::indices/types-exists.asciidoc[]
 
+include::indices/get-alias.asciidoc[]
+
 include::indices/alias-exists.asciidoc[]
 
 include::indices/aliases.asciidoc[]

docs/reference/indices/alias-exists.asciidoc

@@ -37,8 +37,7 @@ HEAD /_alias/alias1
 
 `<alias>`::
 (Required, string)
-Comma-separated list or wildcard expression of index alias names
+include::{docdir}/rest-api/common-parms.asciidoc[tag=index-alias]
-used to limit the request.
 
 include::{docdir}/rest-api/common-parms.asciidoc[tag=index]
 

docs/reference/indices/aliases.asciidoc

@@ -458,120 +458,3 @@ DELETE /logs_20162801/_alias/current_day
 --------------------------------------------------
 // CONSOLE
 // TEST[continued]
-
-[float]
-[[alias-retrieving]]
-==== Retrieving existing aliases
-
-The get index alias API allows to filter by
-alias name and index name. This api redirects to the master and fetches
-the requested index aliases, if available. This api only serialises the
-found index aliases.
-
-Possible options:
-[horizontal]
-`index`::
-    The index name to get aliases for. Partial names are
-    supported via wildcards, also multiple index names can be specified
-    separated with a comma. Also the alias name for an index can be used.
-
-`alias`::
-    The name of alias to return in the response. Like the index
-    option, this option supports wildcards and the option the specify
-    multiple alias names separated by a comma.
-
-`ignore_unavailable`::
-    What to do if an specified index name doesn't
-    exist. If set to `true` then those indices are ignored.
-
-The rest endpoint is: `/{index}/_alias/{alias}`.
-
-[float]
-===== Examples:
-
-All aliases for the index `logs_20162801`:
-
-[source,js]
---------------------------------------------------
-GET /logs_20162801/_alias/*
---------------------------------------------------
-// CONSOLE
-// TEST[continued]
-
-Response:
-
-[source,js]
---------------------------------------------------
-{
- "logs_20162801" : {
-   "aliases" : {
-     "2016" : {
-       "filter" : {
-         "term" : {
-           "year" : 2016
-         }
-       }
-     }
-   }
- }
-}
---------------------------------------------------
-// TESTRESPONSE
-
-All aliases with the name 2016 in any index:
-
-[source,js]
---------------------------------------------------
-GET /_alias/2016
---------------------------------------------------
-// CONSOLE
-// TEST[continued]
-
-Response:
-
-[source,js]
---------------------------------------------------
-{
-  "logs_20162801" : {
-    "aliases" : {
-      "2016" : {
-        "filter" : {
-          "term" : {
-            "year" : 2016
-          }
-        }
-      }
-    }
-  }
-}
---------------------------------------------------
-// TESTRESPONSE
-
-All aliases that start with 20 in any index:
-
-[source,js]
---------------------------------------------------
-GET /_alias/20*
---------------------------------------------------
-// CONSOLE
-// TEST[continued]
-
-Response:
-
-[source,js]
---------------------------------------------------
-{
-  "logs_20162801" : {
-    "aliases" : {
-      "2016" : {
-        "filter" : {
-          "term" : {
-            "year" : 2016
-          }
-        }
-      }
-    }
-  }
-}
---------------------------------------------------
-// TESTRESPONSE

docs/reference/indices/get-alias.asciidoc

@@ -0,0 +1,185 @@
+[[indices-get-alias]]
+=== Get index alias API
+++++
+<titleabbrev>Get index alias</titleabbrev>
+++++
+
+Returns information about one or more index aliases.
+
+include::alias-exists.asciidoc[tag=index-alias-def]
+
+[source,js]
+----
+GET /twitter/_alias/alias1
+----
+// CONSOLE
+// TEST[setup:twitter]
+// TEST[s/^/PUT twitter\/_alias\/alias1\n/]
+
+
+[[get-alias-api-request]]
+==== {api-request-title}
+
+`GET /_alias`
+
+`GET /_alias/<alias>`
+
+`GET /<index>/_alias/<alias>`
+
+
+[[get-alias-api-path-params]]
+==== {api-path-parms-title}
+
+`<alias>`::
+(Optional, string)
+include::{docdir}/rest-api/common-parms.asciidoc[tag=index-alias]
++
+To retrieve information for all index aliases,
+use a value of `_all` or `*`.
+
+include::{docdir}/rest-api/common-parms.asciidoc[tag=index]
+
+
+[[get-alias-api-query-params]]
+==== {api-query-parms-title}
+
+include::{docdir}/rest-api/common-parms.asciidoc[tag=allow-no-indices]
+
+include::{docdir}/rest-api/common-parms.asciidoc[tag=expand-wildcards]
++
+Defaults to `all`.
+
+include::{docdir}/rest-api/common-parms.asciidoc[tag=index-ignore-unavailable]
+
+include::{docdir}/rest-api/common-parms.asciidoc[tag=local]
+
+
+[[get-alias-api-example]]
+==== {api-examples-title}
+
+[[get-alias-api-all-ex]]
+===== Get all aliases for an index
+
+You can add index aliases during index creation
+using a <<indices-create-index,create index API>> request.
+
+The following create index API request creates the `logs_20302801` index
+with two aliases:
+
+* `current_day`
+* `2030`, which only returns documents
+in the `logs_20302801` index
+with a `year` field value of `2030`
+
+[source,js]
+--------------------------------------------------
+PUT /logs_20302801
+{
+  "aliases" : {
+    "current_day" : {},
+    "2030" : {
+      "filter" : {
+          "term" : {"year" : 2030 }
+      }
+    }
+  }
+}
+--------------------------------------------------
+// CONSOLE
+
+The following get index alias API request returns all aliases
+for the index `logs_20302801`:
+
+[source,js]
+--------------------------------------------------
+GET /logs_20302801/_alias/*
+--------------------------------------------------
+// CONSOLE
+// TEST[continued]
+
+The API returns the following response:
+
+[source,js]
+--------------------------------------------------
+{
+ "logs_20302801" : {
+   "aliases" : {
+    "current_day" : {
+    },
+     "2030" : {
+       "filter" : {
+         "term" : {
+           "year" : 2030
+         }
+       }
+     }
+   }
+ }
+}
+--------------------------------------------------
+// TESTRESPONSE
+
+
+[[get-alias-api-named-ex]]
+===== Get a specific alias
+
+The following index alias API request returns the `2030` alias:
+
+[source,js]
+--------------------------------------------------
+GET /_alias/2030
+--------------------------------------------------
+// CONSOLE
+// TEST[continued]
+
+The API returns the following response:
+
+[source,js]
+--------------------------------------------------
+{
+  "logs_20302801" : {
+    "aliases" : {
+      "2030" : {
+        "filter" : {
+          "term" : {
+            "year" : 2030
+          }
+        }
+      }
+    }
+  }
+}
+--------------------------------------------------
+// TESTRESPONSE
+
+[[get-alias-api-wildcard-ex]]
+===== Get aliases based on a wildcard
+
+The following index alias API request returns any alias that begin with `20`:
+
+[source,js]
+--------------------------------------------------
+GET /_alias/20*
+--------------------------------------------------
+// CONSOLE
+// TEST[continued]
+
+The API returns the following response:
+
+[source,js]
+--------------------------------------------------
+{
+  "logs_20302801" : {
+    "aliases" : {
+      "2030" : {
+        "filter" : {
+          "term" : {
+            "year" : 2030
+          }
+        }
+      }
+    }
+  }
+}
+--------------------------------------------------
+// TESTRESPONSE

docs/reference/rest-api/common-parms.asciidoc

@@ -1,4 +1,9 @@
 
+tag::index-alias[]
+Comma-separated list or wildcard expression of index alias names
+used to limit the request.
+end::index-alias[]
+
 tag::allow-no-indices[]
 `allow_no_indices`::
 (Optional, boolean) If `true`, the request returns an error if a wildcard