diff --git a/client/rest/src/main/java/org/opensearch/client/Response.java b/client/rest/src/main/java/org/opensearch/client/Response.java
index c758826b776ba..b062d937ed630 100644
--- a/client/rest/src/main/java/org/opensearch/client/Response.java
+++ b/client/rest/src/main/java/org/opensearch/client/Response.java
@@ -147,7 +147,7 @@ public HttpEntity getEntity() {
      * @return {@code true} if the input string matches the specification
      */
     private static boolean matchWarningHeaderPatternByPrefix(final String s) {
-        return s.startsWith("299 OpenSearch-") || s.startsWith("299 Elasticsearch-");
+        return s.startsWith("299 OpenSearch-");
     }
 
     /**
diff --git a/server/src/main/java/org/opensearch/common/logging/HeaderWarning.java b/server/src/main/java/org/opensearch/common/logging/HeaderWarning.java
index df5a94ccd34e4..44eefe1e78580 100644
--- a/server/src/main/java/org/opensearch/common/logging/HeaderWarning.java
+++ b/server/src/main/java/org/opensearch/common/logging/HeaderWarning.java
@@ -60,8 +60,7 @@ public class HeaderWarning {
      * Regular expression to test if a string matches the RFC7234 specification for warning headers. This pattern assumes that the warn code
      * is always 299. Further, this pattern assumes that the warn agent represents a version of OpenSearch including the build hash.
      */
-    public static final Pattern WARNING_HEADER_PATTERN = Pattern.compile("299 " + // warn code
-        "(?:Elasticsearch-|OpenSearch-)" + // warn agent (note: Elasticsearch needed for bwc mixedCluster testing)
+    public static final Pattern WARNING_HEADER_PATTERN = Pattern.compile("299 OpenSearch-" + // warn code
         "\\d+\\.\\d+\\.\\d+(?:-(?:alpha|beta|rc)\\d+)?(?:-SNAPSHOT)?-" + // warn agent
         "(?:[a-f0-9]{7}(?:[a-f0-9]{33})?|unknown) " + // warn agent
         "\"((?:\t| |!|[\\x23-\\x5B]|[\\x5D-\\x7E]|[\\x80-\\xFF]|\\\\|\\\\\")*)\"( " + // quoted warning value, captured
diff --git a/server/src/main/java/org/opensearch/common/logging/LogConfigurator.java b/server/src/main/java/org/opensearch/common/logging/LogConfigurator.java
index c0405f9e52b77..4438bf53fd62c 100644
--- a/server/src/main/java/org/opensearch/common/logging/LogConfigurator.java
+++ b/server/src/main/java/org/opensearch/common/logging/LogConfigurator.java
@@ -66,9 +66,7 @@
 import java.nio.file.SimpleFileVisitor;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.EnumSet;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Objects;
 import java.util.Set;
@@ -182,7 +180,6 @@ private static void configure(final Settings settings, final Path configsPath, f
 
         final LoggerContext context = (LoggerContext) LogManager.getContext(false);
 
-        final Set<String> locationsWithDeprecatedPatterns = Collections.synchronizedSet(new HashSet<>());
         final List<AbstractConfiguration> configurations = new ArrayList<>();
         final PropertiesConfigurationFactory factory = new PropertiesConfigurationFactory();
         final Set<FileVisitOption> options = EnumSet.of(FileVisitOption.FOLLOW_LINKS);
@@ -206,12 +203,8 @@ public FileVisitResult visitFile(final Path file, final BasicFileAttributes attr
 
         // Redirect stdout/stderr to log4j. While we ensure Elasticsearch code does not write to those streams,
         // third party libraries may do that
-        System.setOut(
-            new PrintStream(new LoggingOutputStream(LogManager.getLogger("stdout"), Level.INFO), false, StandardCharsets.UTF_8.name())
-        );
-        System.setErr(
-            new PrintStream(new LoggingOutputStream(LogManager.getLogger("stderr"), Level.WARN), false, StandardCharsets.UTF_8.name())
-        );
+        System.setOut(new PrintStream(new LoggingOutputStream(LogManager.getLogger("stdout"), Level.INFO), false, StandardCharsets.UTF_8));
+        System.setErr(new PrintStream(new LoggingOutputStream(LogManager.getLogger("stderr"), Level.WARN), false, StandardCharsets.UTF_8));
     }
 
     private static void configureStatusLogger() {
diff --git a/server/src/main/java/org/opensearch/common/logging/LoggerMessageFormat.java b/server/src/main/java/org/opensearch/common/logging/LoggerMessageFormat.java
index ad9981809ae3a..a0dec5b8d0b70 100644
--- a/server/src/main/java/org/opensearch/common/logging/LoggerMessageFormat.java
+++ b/server/src/main/java/org/opensearch/common/logging/LoggerMessageFormat.java
@@ -79,34 +79,34 @@ public static String format(final String prefix, final String messagePattern, fi
                     return messagePattern;
                 } else { // add the tail string which contains no variables and return
                     // the result.
-                    sbuf.append(messagePattern.substring(i, messagePattern.length()));
+                    sbuf.append(messagePattern.substring(i));
                     return sbuf.toString();
                 }
             } else {
                 if (isEscapedDelimiter(messagePattern, j)) {
                     if (!isDoubleEscaped(messagePattern, j)) {
                         L--; // DELIM_START was escaped, thus should not be incremented
-                        sbuf.append(messagePattern.substring(i, j - 1));
+                        sbuf.append(messagePattern, i, j - 1);
                         sbuf.append(DELIM_START);
                         i = j + 1;
                     } else {
                         // The escape character preceding the delimiter start is
                         // itself escaped: "abc x:\\{}"
                         // we have to consume one backward slash
-                        sbuf.append(messagePattern.substring(i, j - 1));
-                        deeplyAppendParameter(sbuf, argArray[L], new HashSet<Object[]>());
+                        sbuf.append(messagePattern, i, j - 1);
+                        deeplyAppendParameter(sbuf, argArray[L], new HashSet<>());
                         i = j + 2;
                     }
                 } else {
                     // normal case
-                    sbuf.append(messagePattern.substring(i, j));
-                    deeplyAppendParameter(sbuf, argArray[L], new HashSet<Object[]>());
+                    sbuf.append(messagePattern, i, j);
+                    deeplyAppendParameter(sbuf, argArray[L], new HashSet<>());
                     i = j + 2;
                 }
             }
         }
         // append the characters following the last {} pair.
-        sbuf.append(messagePattern.substring(i, messagePattern.length()));
+        sbuf.append(messagePattern.substring(i));
         return sbuf.toString();
     }
 
@@ -116,19 +116,11 @@ static boolean isEscapedDelimiter(String messagePattern, int delimiterStartIndex
             return false;
         }
         char potentialEscape = messagePattern.charAt(delimiterStartIndex - 1);
-        if (potentialEscape == ESCAPE_CHAR) {
-            return true;
-        } else {
-            return false;
-        }
+        return potentialEscape == ESCAPE_CHAR;
     }
 
     static boolean isDoubleEscaped(String messagePattern, int delimiterStartIndex) {
-        if (delimiterStartIndex >= 2 && messagePattern.charAt(delimiterStartIndex - 2) == ESCAPE_CHAR) {
-            return true;
-        } else {
-            return false;
-        }
+        return delimiterStartIndex >= 2 && messagePattern.charAt(delimiterStartIndex - 2) == ESCAPE_CHAR;
     }
 
     private static void deeplyAppendParameter(StringBuilder sbuf, Object o, Set<Object[]> seen) {