Make _source.enabled configurable for ElasticMeterRegistry (#2363)

But also warn about the costs associated as a mitigation to this mistakenly being enabled in a production environment.

Closes gh-1629

Author: izeye

implementations/micrometer-registry-elastic/src/main/java/io/micrometer/elastic/DefaultIndexTemplateCreator.java

@@ -34,7 +34,7 @@ class DefaultIndexTemplateCreator implements IndexTemplateCreator {
     private final Logger logger = LoggerFactory.getLogger(DefaultIndexTemplateCreator.class);
 
     private final String indexTemplateRequest = "{\n" + "  \"index_patterns\": [\"%s*\"],\n" + "  \"template\": {\n"
-            + "    \"mappings\": {\n" + "      \"_source\": {\n" + "        \"enabled\": false\n" + "      },\n"
+            + "    \"mappings\": {\n" + "      \"_source\": {\n" + "        \"enabled\": %b\n" + "      },\n"
             + "      \"properties\": {\n" + "        \"name\": { \"type\": \"keyword\" },\n"
             + "        \"count\": { \"type\": \"double\", \"index\": false },\n"
             + "        \"value\": { \"type\": \"double\", \"index\": false },\n"
@@ -81,9 +81,10 @@ public IndexTemplateStatus fetchIndexTemplateStatus(ElasticConfig configuration)
     @Override
     public void createIndexTemplate(ElasticConfig configuration) throws Throwable {
         String indexPattern = configuration.index() + configuration.indexDateSeparator();
+        boolean enableSource = configuration.enableSource();
         HttpSender.Request.Builder request = this.httpClient.put(configuration.host() + INDEX_TEMPLATE_PATH);
         configureAuthentication(configuration, request);
-        request.withJsonContent(String.format(indexTemplateRequest, indexPattern))
+        request.withJsonContent(String.format(indexTemplateRequest, indexPattern, enableSource))
             .send()
             .onError(response -> logger.error("Failed to create index template in Elastic: {}", response.body()));
     }

implementations/micrometer-registry-elastic/src/main/java/io/micrometer/elastic/ElasticConfig.java

@@ -178,6 +178,16 @@ default String documentType() {
         return getString(this, "documentType").orElse("doc");
     }
 
+    /**
+     * Enable {@literal _source} in the index template. Default is: {@code false}
+     * @return whether {@literal _source} will be enabled in the index template used with
+     * {@link #autoCreateIndex()}
+     * @since 1.14.0
+     */
+    default boolean enableSource() {
+        return getBoolean(this, "enableSource").orElse(false);
+    }
+
     @Override
     default Validated<?> validate() {
         return checkAll(this, c -> StepRegistryConfig.validate(c), checkRequired("host", ElasticConfig::host),

implementations/micrometer-registry-elastic/src/main/java/io/micrometer/elastic/ElasticMeterRegistry.java

@@ -153,6 +153,9 @@ private void createIndexTemplateIfNeeded() {
         if (this.checkedForIndexTemplate || !this.config.autoCreateIndex()) {
             return;
         }
+        if (config.enableSource()) {
+            logger.warn("'_source' field is enabled. Disable '_source' field to save space and reduce I/O.");
+        }
         attemptIndexTemplateCreation(new DefaultIndexTemplateCreator(this.httpClient));
         if (!this.checkedForIndexTemplate) {
             logger.debug("Attempt to create index template using legacy /_template/ endpoint");

implementations/micrometer-registry-elastic/src/main/java/io/micrometer/elastic/LegacyIndexTemplateCreator.java

@@ -34,7 +34,7 @@ class LegacyIndexTemplateCreator implements IndexTemplateCreator {
     private final Logger logger = LoggerFactory.getLogger(LegacyIndexTemplateCreator.class);
 
     private final String indexTemplateRequest = "{\n" + "  \"index_patterns\": [\"%s*\"],\n" + "  \"mappings\": {\n"
-            + "    \"_source\": {\n" + "      \"enabled\": false\n" + "    },\n" + "    \"properties\": {\n"
+            + "    \"_source\": {\n" + "      \"enabled\": %b\n" + "    },\n" + "    \"properties\": {\n"
             + "      \"name\": { \"type\": \"keyword\" },\n"
             + "      \"count\": { \"type\": \"double\", \"index\": false },\n"
             + "      \"value\": { \"type\": \"double\", \"index\": false },\n"
@@ -80,9 +80,10 @@ public IndexTemplateStatus fetchIndexTemplateStatus(ElasticConfig configuration)
     @Override
     public void createIndexTemplate(ElasticConfig configuration) throws Throwable {
         String indexPattern = configuration.index() + configuration.indexDateSeparator();
+        boolean enableSource = configuration.enableSource();
         HttpSender.Request.Builder request = this.httpClient.put(configuration.host() + INDEX_TEMPLATE_PATH);
         configureAuthentication(configuration, request);
-        request.withJsonContent(String.format(indexTemplateRequest, indexPattern))
+        request.withJsonContent(String.format(indexTemplateRequest, indexPattern, enableSource))
             .send()
             .onError(response -> logger.error("Failed to create index template in Elastic: {}", response.body()));
     }