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/ElasticConfig.java

@@ -181,6 +181,17 @@ default String apiKeyCredentials() {
         return getSecret(this, "apiKeyCredentials").orElse(null);
     }
 
+    /**
+     * Enable {@literal _source} in the index template.
+     * Default is: {@code false}
+     *
+     * @return whether {@literal _source} will be enabled in the index template
+     * @since 2.0.0
+     */
+    default boolean enableSource() {
+        return getBoolean(this, "enableSource").orElse(false);
+    }
+
     @Override
     default Validated<?> validate() {
         return checkAll(this,

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

@@ -38,7 +38,6 @@
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
-import java.util.function.Function;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -100,14 +99,6 @@ public class ElasticMeterRegistry extends StepMeterRegistry {
             "    \"index\": false\n" +
             "  }\n" +
             "}";
-    private static final Function<String, String> TEMPLATE_BODY_AFTER_VERSION_7 = (indexPrefix) -> "{\n" +
-            "  \"index_patterns\": [\"" + indexPrefix + "*\"],\n" +
-            "  \"mappings\": {\n" +
-            "    \"_source\": {\n" +
-            "      \"enabled\": false\n" +
-            "    },\n" + TEMPLATE_PROPERTIES +
-            "  }\n" +
-            "}";
 
     private static final Pattern MAJOR_VERSION_PATTERN = Pattern.compile("\"number\" *: *\"([\\d]+)");
 
@@ -192,7 +183,15 @@ private void createIndexTemplateIfNeeded() {
     }
 
     private String getTemplateBody() {
-        return TEMPLATE_BODY_AFTER_VERSION_7.apply(config.index() + config.indexDateSeparator());
+        String indexPrefix = config.index() + config.indexDateSeparator();
+        return "{\n" +
+                "  \"index_patterns\": [\"" + indexPrefix + "*\"],\n" +
+                "  \"mappings\": {\n" +
+                "    \"_source\": {\n" +
+                "      \"enabled\": " + config.enableSource() + "\n" +
+                "    },\n" + TEMPLATE_PROPERTIES +
+                "  }\n" +
+                "}";
     }
 
     private HttpSender.Request.Builder connect(HttpSender.Method method, String uri) {
@@ -212,6 +211,10 @@ private HttpSender.Request.Builder authentication(HttpSender.Request.Builder req
     protected void publish() {
         createIndexTemplateIfNeeded();
 
+        if (config.enableSource()) {
+            logger.warn("'_source' field is enabled. Disable '_source' field to save space and reduce I/O.");
+        }
+
         String uri = config.host() + "/" + indexName() + "/_bulk";
         for (List<Meter> batch : MeterPartition.partition(this, config.batchSize())) {
             try {