YARN-10970. Standby RM should expose prom endpoint (#3480)

Reviewed-by: Adam Antal <adamantal@apache.org>
Signed-off-by: Akira Ajisaka <aajisaka@apache.org>
(cherry picked from commit 4bd0c36189f6859e3b0fde922fd8b25d0c756233)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-client/src/test/java/org/apache/hadoop/yarn/client/TestRMFailover.java

@@ -295,7 +295,7 @@ public class TestRMFailover extends ClientBaseWithFixes {
     assertEquals(redirectURL,rm1Url + "/metrics");
 
 
-    // standby RM links /conf, /stacks, /logLevel, /static, /logs, /jmx
+    // standby RM links /conf, /stacks, /logLevel, /static, /logs, /jmx, /prom
     // /cluster/cluster as well as webService
     // /ws/v1/cluster/info should not be redirected to active RM
     redirectURL = getRedirectURL(rm2Url + "/cluster/cluster");
@@ -319,6 +319,9 @@ public class TestRMFailover extends ClientBaseWithFixes {
     redirectURL = getRedirectURL(rm2Url + "/jmx?param1=value1+x&param2=y");
     assertNull(redirectURL);
 
+    redirectURL = getRedirectURL(rm2Url + "/prom");
+    assertNull(redirectURL);
+
     redirectURL = getRedirectURL(rm2Url + "/ws/v1/cluster/info");
     assertNull(redirectURL);
 

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/webapp/RMWebAppFilter.java

@@ -70,7 +70,7 @@ public class RMWebAppFilter extends GuiceContainer {
   // define a set of URIs which do not need to do redirection
   private static final Set<String> NON_REDIRECTED_URIS = Sets.newHashSet(
       "/conf", "/stacks", "/logLevel", "/logs", IsActiveServlet.PATH_SPEC,
-      "/jmx");
+      "/jmx", "/prom");
   private String path;
   private boolean ahsEnabled;
   private String ahsPageURLPrefix;