Fix slash root issues in es7 client (#6707)

Signed-off-by: NGao Hongtao <hanahmily@gmail.com>

CHANGES.md

@@ -74,7 +74,7 @@ Release Notes.
 * Make the flushing metrics operation concurrent.
 * Fix ALS K8SServiceRegistry didn't remove the correct entry.
 * Using "service.istio.io/canonical-name" to replace "app" label to resolve Envoy ALS service name.
-* Append the root slash(/) to getIndex and getTemplate requests in ES client.
+* Append the root slash(/) to getIndex and getTemplate requests in ES(6 and 7) client.
 * Fix `disable` statement not working. This bug exists since 8.0.0.
 * Remove the useless metric in `vm.yaml`.
 

oap-server/server-storage-plugin/storage-elasticsearch7-plugin/src/main/java/org/apache/skywalking/oap/server/storage/plugin/elasticsearch7/client/ElasticSearch7Client.java

@@ -175,7 +175,7 @@ public class ElasticSearch7Client extends ElasticSearchClient {
         indexName = formatIndexName(indexName);
         try {
             Response response = client.getLowLevelClient()
-                                      .performRequest(new Request(HttpGet.METHOD_NAME, indexName));
+                                      .performRequest(new Request(HttpGet.METHOD_NAME, "/" + indexName));
             int statusCode = response.getStatusLine().getStatusCode();
             if (statusCode != HttpStatus.SC_OK) {
                 healthChecker.health();
@@ -218,7 +218,7 @@ public class ElasticSearch7Client extends ElasticSearchClient {
         name = formatIndexName(name);
         try {
             Response response = client.getLowLevelClient()
-                                      .performRequest(new Request(HttpGet.METHOD_NAME, "_template/" + name));
+                                      .performRequest(new Request(HttpGet.METHOD_NAME, "/_template/" + name));
             int statusCode = response.getStatusLine().getStatusCode();
             if (statusCode != HttpStatus.SC_OK) {
                 healthChecker.health();