Add index.data_path setting

This allows specifying the path an index will be at.

`index.data_path` is specified in the settings when creating an index,
and can not be dynamically changed.

An example request would look like:

POST /myindex
{
  "settings": {
    "number_of_shards": 2,
    "data_path": "/tmp/myindex"
  }
}

And would put data in /tmp/myindex/0/index/0 and /tmp/myindex/0/index/1

Since this can be used to write data to arbitrary locations on disk, it
requires enabling the `node.enable_custom_paths` setting in
elasticsearch.yml on all nodes.

Relates to #8976

src/main/java/org/elasticsearch/action/admin/indices/create/CreateIndexRequest.java

@@ -48,9 +48,9 @@
 
 import static com.google.common.collect.Maps.newHashMap;
 import static org.elasticsearch.action.ValidateActions.addValidationError;
+import static org.elasticsearch.common.settings.ImmutableSettings.Builder.EMPTY_SETTINGS;
 import static org.elasticsearch.common.settings.ImmutableSettings.readSettingsFromStream;
 import static org.elasticsearch.common.settings.ImmutableSettings.writeSettingsToStream;
-import static org.elasticsearch.common.settings.ImmutableSettings.Builder.EMPTY_SETTINGS;
 
 /**
  * A request to create an index. Best created with {@link org.elasticsearch.client.Requests#createIndexRequest(String)}.

src/main/java/org/elasticsearch/cluster/metadata/IndexMetaData.java

@@ -167,6 +167,7 @@ public static State fromString(String state) {
     public static final String SETTING_UUID = "index.uuid";
     public static final String SETTING_LEGACY_ROUTING_HASH_FUNCTION = "index.legacy.routing.hash.type";
     public static final String SETTING_LEGACY_ROUTING_USE_TYPE = "index.legacy.routing.use_type";
+    public static final String SETTING_DATA_PATH = "index.data_path";
     public static final String INDEX_UUID_NA_VALUE = "_na_";
 
     // hard-coded hash function as of 2.0

src/main/java/org/elasticsearch/cluster/metadata/MetaDataCreateIndexService.java

@@ -26,6 +26,7 @@
 import com.google.common.collect.Maps;
 import org.apache.lucene.util.CollectionUtil;
 import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.ElasticsearchIllegalArgumentException;
 import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.ActionRunnable;
@@ -57,13 +58,15 @@
 import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.env.Environment;
+import org.elasticsearch.env.NodeEnvironment;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.mapper.DocumentMapper;
 import org.elasticsearch.index.mapper.MapperParsingException;
 import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.query.IndexQueryParserService;
 import org.elasticsearch.index.IndexService;
 import org.elasticsearch.indices.IndexAlreadyExistsException;
+import org.elasticsearch.indices.IndexCreationException;
 import org.elasticsearch.indices.IndicesService;
 import org.elasticsearch.indices.InvalidIndexNameException;
 import org.elasticsearch.river.RiverIndexName;
@@ -101,11 +104,13 @@ public class MetaDataCreateIndexService extends AbstractComponent {
     private final String riverIndexName;
     private final AliasValidator aliasValidator;
     private final IndexTemplateFilter indexTemplateFilter;
+    private final NodeEnvironment nodeEnv;
 
     @Inject
-    public MetaDataCreateIndexService(Settings settings, Environment environment, ThreadPool threadPool, ClusterService clusterService, IndicesService indicesService,
-                                      AllocationService allocationService, MetaDataService metaDataService, Version version, @RiverIndexName String riverIndexName,
-                                      AliasValidator aliasValidator, Set<IndexTemplateFilter> indexTemplateFilters) {
+    public MetaDataCreateIndexService(Settings settings, Environment environment, ThreadPool threadPool, ClusterService clusterService,
+                                      IndicesService indicesService, AllocationService allocationService, MetaDataService metaDataService,
+                                      Version version, @RiverIndexName String riverIndexName, AliasValidator aliasValidator,
+                                      Set<IndexTemplateFilter> indexTemplateFilters, NodeEnvironment nodeEnv) {
         super(settings);
         this.environment = environment;
         this.threadPool = threadPool;
@@ -116,6 +121,7 @@ public MetaDataCreateIndexService(Settings settings, Environment environment, Th
         this.version = version;
         this.riverIndexName = riverIndexName;
         this.aliasValidator = aliasValidator;
+        this.nodeEnv = nodeEnv;
 
         if (indexTemplateFilters.isEmpty()) {
             this.indexTemplateFilter = DEFAULT_INDEX_TEMPLATE_FILTER;
@@ -554,6 +560,11 @@ public int compare(IndexTemplateMetaData o1, IndexTemplateMetaData o2) {
 
     private void validate(CreateIndexClusterStateUpdateRequest request, ClusterState state) throws ElasticsearchException {
         validateIndexName(request.index(), state);
+        String customPath = request.settings().get(IndexMetaData.SETTING_DATA_PATH, null);
+        if (customPath != null && nodeEnv.isCustomPathsEnabled() == false) {
+            throw new IndexCreationException(new Index(request.index()),
+                    new ElasticsearchIllegalArgumentException("custom data_paths for indices is disabled"));
+        }
     }
 
     private static class DefaultIndexTemplateFilter implements IndexTemplateFilter {