Add template simulation API for simulating template composition

client/rest-high-level/src/test/java/org/elasticsearch/client/RestHighLevelClientTests.java

@@ -803,7 +803,8 @@ public void testApiNamingConventions() throws Exception {
             "scripts_painless_execute",
             "indices.create_data_stream",
             "indices.get_data_stream",
-            "indices.delete_data_stream"
+            "indices.delete_data_stream",
+            "indices.simulate_template"
         };
         //These API are not required for high-level client feature completeness
         String[] notRequiredApi = new String[] {

docs/reference/indices/index-templates.asciidoc

@@ -96,7 +96,7 @@ PUT _index_template/template_1
 
 [source,console]
 --------------------------------------------------
-DELETE _index_template/template_*
+DELETE _index_template/*
 DELETE _component_template/*
 --------------------------------------------------
 // TEARDOWN
@@ -291,6 +291,96 @@ PUT /_index_template/template_1
 In this case, an index matching `t*` will have three primary shards. If the order of composed
 templates were reversed, the index would have two primary shards.
 
+
+[[simulating-templates]]
+===== Simulating template composition
+
+Since templates can be composed not only of multiple component templates, but also the index
+template itself, there are two simulation APIs to determine what the resulting index settings will
+be.
+
+To simulate the settings that would be applied to a matching index name:
+
+[source,console]
+--------------------------------------------------
+POST /_index_template/_simulate_index/myindex
+--------------------------------------------------
+
+To simulate the settings that would be applied from a particular template:
+
+[source,console]
+--------------------------------------------------
+POST /_index_template/_simulate/template_1
+
+POST /_index_template/_simulate
+{
+  "index_patterns": ["foo"],
+  "template": {
+    "settings": {
+      "number_of_replicas": 0
+    }
+  }
+}
+--------------------------------------------------
+
+
+Here's an example demonstrating simulating both an index name and template name:
+
+[source,console]
+--------------------------------------------------
+PUT /_component_template/ct1 <1>
+{
+  "template": {
+    "settings": {
+      "index.number_of_shards": 2
+    }
+  }
+}
+
+PUT /_component_template/ct2 <2>
+{
+  "template": {
+    "settings": {
+      "index.number_of_replicas": 0
+    },
+    "mappings": {
+      "properties": {
+        "@timestamp": {
+          "type": "date"
+        }
+      }
+    }
+  }
+}
+
+PUT /_index_template/final-template <3>
+{
+  "index_patterns": ["logdata-*"],
+  "composed_of": ["ct1", "ct2"],
+  "priority": 5
+}
+
+POST /_index_template/_simulate_index/logdata-2019-02-01 <4>
+
+POST /_index_template/_simulate/final-template <5>
+
+POST /_index_template/_simulate <6>
+{
+  "index_patterns": ["mydata-*"],
+  "composed_of": ["ct2"],
+  "priority": 10
+}
+--------------------------------------------------
+<1> Creating a component template (ct1) setting the number of shards to two
+<2> Creating another component template (ct2) setting the number of replicas to zero with mappings
+<3> Creating an index template called "final" template using ct1 and ct2
+<4> Simulate the settings that would be applied for a new index "logdata-2019-02-01"
+<5> Simulate the settings composed using the "final-template" index template
+<6> Simulate the settings composed using a custom specified template
+
+When simulating a template and specifying a template in the body of the request, the simulated
+template is not added to the existing templates, it is only used for the simulation.
+
 ===== Index template with index aliases
 
 You can include <<indices-aliases,index aliases>> in an index template.

rest-api-spec/src/main/resources/rest-api-spec/api/indices.simulate_template.json

@@ -0,0 +1,51 @@
+{
+  "indices.simulate_template":{
+    "documentation":{
+      "url":"https://www.elastic.co/guide/en/elasticsearch/reference/master/indices-templates.html",
+      "description": "Simulate resolving the given template name or body"
+    },
+    "stability":"stable",
+    "url":{
+      "paths":[
+        {
+          "path":"/_index_template/_simulate",
+          "methods":[
+            "POST"
+          ]
+        },
+        {
+          "path":"/_index_template/_simulate/{name}",
+          "methods":[
+            "POST"
+          ],
+          "parts":{
+            "name":{
+              "type":"string",
+              "description":"The name of the index template"
+            }
+          }
+        }
+      ]
+    },
+    "params":{
+      "create":{
+        "type":"boolean",
+        "description":"Whether the index template we optionally defined in the body should only be dry-run added if new or can also replace an existing one",
+        "default":false
+      },
+      "cause":{
+        "type":"string",
+        "description":"User defined reason for dry-run creating the new template for simulation purposes",
+        "default":false
+      },
+      "master_timeout":{
+        "type":"time",
+        "description":"Specify timeout for connection to master"
+      }
+    },
+    "body":{
+      "description":"New index template definition to be simulated, if no index template name is specified",
+      "required":false
+    }
+  }
+}

rest-api-spec/src/main/resources/rest-api-spec/test/indices.simulate_index_template/10_basic.yml

@@ -25,7 +25,7 @@
 
   - match: {template.settings.index.number_of_shards: "1"}
   - match: {template.settings.index.number_of_replicas: "0"}
-  - match: {template.mappings._doc.properties.field.type: "keyword"}
+  - match: {template.mappings.properties.field.type: "keyword"}
   - match: {overlapping: []}
 
 ---
@@ -77,7 +77,7 @@
 
   - match: {template.settings.index.blocks.write: "true"}
   - match: {template.settings.index.number_of_replicas: "2"}
-  - match: {template.mappings._doc.properties.ct_field.type: "keyword"}
+  - match: {template.mappings.properties.ct_field.type: "keyword"}
   - match: {overlapping.0.name: existing_test}
   - match: {overlapping.0.index_patterns: ["te*"]}
   - length: {template.aliases: 1}
@@ -170,7 +170,7 @@
 
   - match: {template.settings.index.number_of_shards: "1"}
   - match: {template.settings.index.number_of_replicas: "0"}
-  - match: {template.mappings._doc.properties.field.type: "keyword"}
+  - match: {template.mappings.properties.field.type: "keyword"}
   - match: {overlapping.0.name: v1_template}
   - match: {overlapping.0.index_patterns: ["t*", "t1*"]}
   - match: {overlapping.1.name: v2_template}

rest-api-spec/src/main/resources/rest-api-spec/test/indices.simulate_template/10_basic.yml

@@ -0,0 +1,146 @@
+---
+"Simulate template without a template in the body":
+  - skip:
+      version: " - 7.99.99"
+      reason: "not yet backported"
+      features: ["default_shards"]
+
+  - do:
+      indices.put_index_template:
+        name: my-template
+        body:
+          index_patterns: other
+          template:
+            settings:
+              number_of_shards:   1
+              number_of_replicas: 0
+            mappings:
+              properties:
+                field:
+                  type: keyword
+
+  - do:
+      indices.simulate_template:
+        name: my-template
+
+  - match: {template.settings.index.number_of_shards: "1"}
+  - match: {template.settings.index.number_of_replicas: "0"}
+  - match: {template.mappings.properties.field.type: "keyword"}
+  - match: {overlapping: []}
+
+---
+"Simulate index template specifying a new template":
+  - skip:
+      version: " - 7.99.99"
+      reason: "not yet backported"
+      features: ["default_shards"]
+
+  - do:
+      indices.put_index_template:
+        name: existing_test
+        body:
+          index_patterns: te*
+          priority: 10
+          template:
+            settings:
+              number_of_shards:   1
+              number_of_replicas: 0
+            mappings:
+              properties:
+                field:
+                  type: keyword
+
+  - do:
+      cluster.put_component_template:
+        name: ct
+        body:
+          template:
+            settings:
+              index.number_of_replicas: 2
+            mappings:
+              properties:
+                ct_field:
+                  type: keyword
+
+  - do:
+      indices.simulate_template:
+        body:
+          index_patterns: te*
+          priority: 15
+          template:
+            settings:
+              index.blocks.write: true
+            aliases:
+              test_alias: {}
+          composed_of: ["ct"]
+
+  - match: {template.settings.index.blocks.write: "true"}
+  - match: {template.settings.index.number_of_replicas: "2"}
+  - match: {template.mappings.properties.ct_field.type: "keyword"}
+  - match: {overlapping.0.name: existing_test}
+  - match: {overlapping.0.index_patterns: ["te*"]}
+  - length: {template.aliases: 1}
+  - is_true: template.aliases.test_alias
+
+---
+"Simulate template matches overlapping V1 and V2 templates":
+  - skip:
+      version: " - 7.99.99"
+      reason: "not yet backported"
+      features: ["allowed_warnings", "default_shards"]
+
+  - do:
+      indices.put_template:
+        name: v1_template
+        body:
+          index_patterns: [t*, t1*]
+          settings:
+            number_of_shards:   5
+
+  - do:
+      allowed_warnings:
+        - "index template [v2_template] has index patterns [te*] matching patterns from existing older templates [v1_template] with patterns
+        (v1_template => [t*, t1*]); this template [v2_template] will take precedence during new index creation"
+      indices.put_index_template:
+        name: v2_template
+        body:
+          index_patterns: te*
+          priority: 10
+          template:
+            settings:
+              number_of_shards:   10
+              number_of_replicas: 2
+            mappings:
+              properties:
+                field:
+                  type: text
+
+  - do:
+      allowed_warnings:
+        - "index template [winning_v2_template] has index patterns [te*] matching patterns from existing older templates [v1_template] with patterns
+        (v1_template => [t*, t1*]); this template [winning_v2_template] will take precedence during new index creation"
+      indices.put_index_template:
+        name: winning_v2_template
+        body:
+          index_patterns: te*
+          priority: 20
+          template:
+            settings:
+              number_of_shards:   1
+              number_of_replicas: 0
+            mappings:
+              properties:
+                field:
+                  type: keyword
+
+  - do:
+      indices.simulate_template:
+        name: winning_v2_template
+
+  - match: {template.settings.index.number_of_shards: "1"}
+  - match: {template.settings.index.number_of_replicas: "0"}
+  - match: {template.mappings.properties.field.type: "keyword"}
+  - match: {overlapping.0.name: v1_template}
+  - match: {overlapping.0.index_patterns: ["t*", "t1*"]}
+  - match: {overlapping.1.name: v2_template}
+  - match: {overlapping.1.index_patterns: ["te*"]}

server/src/main/java/org/elasticsearch/action/ActionModule.java

@@ -160,7 +160,9 @@
 import org.elasticsearch.action.admin.indices.template.get.TransportGetIndexTemplateV2Action;
 import org.elasticsearch.action.admin.indices.template.get.TransportGetIndexTemplatesAction;
 import org.elasticsearch.action.admin.indices.template.post.SimulateIndexTemplateAction;
+import org.elasticsearch.action.admin.indices.template.post.SimulateTemplateAction;
 import org.elasticsearch.action.admin.indices.template.post.TransportSimulateIndexTemplateAction;
+import org.elasticsearch.action.admin.indices.template.post.TransportSimulateTemplateAction;
 import org.elasticsearch.action.admin.indices.template.put.PutComponentTemplateAction;
 import org.elasticsearch.action.admin.indices.template.put.PutIndexTemplateAction;
 import org.elasticsearch.action.admin.indices.template.put.PutIndexTemplateV2Action;
@@ -313,7 +315,6 @@
 import org.elasticsearch.rest.action.admin.indices.RestIndicesShardStoresAction;
 import org.elasticsearch.rest.action.admin.indices.RestIndicesStatsAction;
 import org.elasticsearch.rest.action.admin.indices.RestOpenIndexAction;
-import org.elasticsearch.rest.action.admin.indices.RestSimulateIndexTemplateAction;
 import org.elasticsearch.rest.action.admin.indices.RestPutComponentTemplateAction;
 import org.elasticsearch.rest.action.admin.indices.RestPutIndexTemplateAction;
 import org.elasticsearch.rest.action.admin.indices.RestPutIndexTemplateV2Action;
@@ -322,6 +323,8 @@
 import org.elasticsearch.rest.action.admin.indices.RestRefreshAction;
 import org.elasticsearch.rest.action.admin.indices.RestResizeHandler;
 import org.elasticsearch.rest.action.admin.indices.RestRolloverIndexAction;
+import org.elasticsearch.rest.action.admin.indices.RestSimulateIndexTemplateAction;
+import org.elasticsearch.rest.action.admin.indices.RestSimulateTemplateAction;
 import org.elasticsearch.rest.action.admin.indices.RestSyncedFlushAction;
 import org.elasticsearch.rest.action.admin.indices.RestUpdateSettingsAction;
 import org.elasticsearch.rest.action.admin.indices.RestUpgradeActionDeprecated;
@@ -540,6 +543,7 @@ public <Request extends ActionRequest, Response extends ActionResponse> void reg
         actions.register(GetIndexTemplateV2Action.INSTANCE, TransportGetIndexTemplateV2Action.class);
         actions.register(DeleteIndexTemplateV2Action.INSTANCE, TransportDeleteIndexTemplateV2Action.class);
         actions.register(SimulateIndexTemplateAction.INSTANCE, TransportSimulateIndexTemplateAction.class);
+        actions.register(SimulateTemplateAction.INSTANCE, TransportSimulateTemplateAction.class);
         actions.register(ValidateQueryAction.INSTANCE, TransportValidateQueryAction.class);
         actions.register(RefreshAction.INSTANCE, TransportRefreshAction.class);
         actions.register(FlushAction.INSTANCE, TransportFlushAction.class);
@@ -690,6 +694,7 @@ public void initRestHandlers(Supplier<DiscoveryNodes> nodesInCluster) {
         registerHandler.accept(new RestGetIndexTemplateV2Action());
         registerHandler.accept(new RestDeleteIndexTemplateV2Action());
         registerHandler.accept(new RestSimulateIndexTemplateAction());
+        registerHandler.accept(new RestSimulateTemplateAction());
 
         registerHandler.accept(new RestPutMappingAction());
         registerHandler.accept(new RestGetMappingAction());