Get exception Unable to retrieve gadget xml. HTTP error 504 when adding Confluence gadget to JIRA dashboard

0com.atlassian.gadgets.GadgetParsingException: com.atlassian.gadgets.GadgetParsingException: org.apache.shindig.gadgets.GadgetException: Unable to retrieve gadget xml. HTTP error 504
	at com.atlassian.gadgets.directory.internal.impl.ConfigurableExternalGadgetSpecDirectoryEntryProvider.validateGadgetSpec(ConfigurableExternalGadgetSpecDirectoryEntryProvider.java:140)
	at com.atlassian.gadgets.directory.internal.impl.ConfigurableExternalGadgetSpecDirectoryEntryProvider.access$100(ConfigurableExternalGadgetSpecDirectoryEntryProvider.java:32)
	at com.atlassian.gadgets.directory.internal.impl.ConfigurableExternalGadgetSpecDirectoryEntryProvider$1.doInTransaction(ConfigurableExternalGadgetSpecDirectoryEntryProvider.java:77)
	at com.atlassian.sal.co
re.transaction.HostContextTransactionTemplate$1.doInTransaction(HostContextTransactionTemplate.java:25)
	at com.atlassian.jira.DefaultHostContextAccessor.doInTransaction(DefaultHostContextAccessor.java:34)  <+2> (DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at com.atlassian.plugin.osgi.hostcomponents.impl.DefaultComponentRegistrar$ContextClassLoaderSettingInvocationHandler.invoke(DefaultComponentRegistrar.java:129)
	at com.sun.proxy.$Proxy98.doInTransaction(Unknown Source)  <+2> (DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at com.atlassian.plugin.osgi.bridge.external.HostComponentFactoryBean$DynamicServiceInvocationHandler.invoke(HostComponentFactoryBean.java:154)
	at com.sun.proxy.$Proxy98.doInTransaction(Unknown Source)
	at com.atlassian.sal.core.transaction.HostContextTransactionTemplate.execute(HostContextTransactionTemplate.java:21)  <+2> (DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
	at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.doInvoke(ServiceInvoker.java:58)
	at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.invoke(ServiceInvoker.java:62)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
	at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invokeUnprivileged(ServiceTCCLInterceptor.java:56)
	at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invoke(ServiceTCCLInterceptor.java:39)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.osgi.service.importer.support.LocalBundleContextAdvice.invoke(LocalBundleContextAdvice.java:59)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
	at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
	at com.sun.proxy.$Proxy2640.execute(Unknown Source)
	at com.atlassian.gadgets.directory.internal.impl.ConfigurableExternalGadgetSpecDirectoryEntryProvider.add(ConfigurableExternalGadgetSpecDirectoryEntryProvider.java:68)
	at com.atlassian.gadgets.directory.internal.rest.DirectoryResource.putGadgetInDirectory(DirectoryResource.java:124)  <+3> (NativeMethodAccessorImpl.java:57) (DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)  <+18> (DispatchProviderHelper.java:234) (DispatchProviderHelper.java:100) (DefaultMethodInvocation.java:61) (ExpandInterceptor.java:38) (DefaultMethodInvocation.java:61) (DispatchProviderHelper.java:132) (DispatchProviderHelper.java:230) (ResourceJavaMethodDispatcher.java:75) (HttpMethodRule.java:288) (ResourceClassRule.java:108) (RightHandPathRule.java:147) (RootResourceClassesRule.java:84) (WebApplicationImpl.java:1469) (WebApplicationImpl.java:1400) (WebApplicationImpl.java:1349) (WebApplicationImpl.java:1339) (WebComponent.java:416) (ServletContainer.java:537)
	at com.atlassian.plugins.rest.module.RestDelegatingServletFilter$JerseyOsgiServletContainer.doFilter(RestDelegatingServletFilter.java:178)  <+1> (ServletContainer.java:795)
	at com.atlassian.plugins.rest.module.RestDelegatingServletFilter.doFilter(RestDelegatingServletFilter.java:73)  <+16> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (ServletFilterModuleContainerFilter.java:77) (ServletFilterModuleContainerFilter.java:63) (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66) (RestServletUtilsUpdaterFilter.java:26) (RestServletUtilsUpdaterFilter.java:40) (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66) (ContextFilter.java:25) (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66)
	at com.atlassian.mywork.client.filter.ServingRequestsFilter.doFilter(ServingRequestsFilter.java:37)  <+3> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66)
	at com.atlassian.plugins.cors.CorsFilter.doFilter(CorsFilter.java:65)  <+3> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66)
	at com.atlassian.prettyurls.filter.PrettyUrlsDispatcherFilter.doFilter(PrettyUrlsDispatcherFilter.java:60)  <+3> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66)
	at com.atlassian.prettyurls.filter.PrettyUrlsSiteMeshFilter.doFilter(PrettyUrlsSiteMeshFilter.java:92)  <+3> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66)
	at com.atlassian.prettyurls.filter.PrettyUrlsMatcherFilter.doFilter(PrettyUrlsMatcherFilter.java:56)  <+3> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66)
	at com.atlassian.labs.botkiller.BotKillerFilter.doFilter(BotKillerFilter.java:36)  <+3> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66)
	at com.atlassian.labs.httpservice.resource.ResourceFilter.doFilter(ResourceFilter.java:59)  <+18> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (ServletFilterModuleContainerFilter.java:77) (ServletFilterModuleContainerFilter.java:63) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (AccessLogFilter.java:103) (AccessLogFilter.java:87) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (XsrfTokenAdditionRequestFilter.java:54) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (ChainedFilterStepRunner.java:87) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (IteratingFilterChain.java:46) (DelegatingPluginFilter.java:66)
	at com.atlassian.prettyurls.filter.PrettyUrlsCombinedMatchDispatcherFilter.doFilter(PrettyUrlsCombinedMatchDispatcherFilter.java:61)  <+22> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (ServletFilterModuleContainerFilter.java:77) (ServletFilterModuleContainerFilter.java:63) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (SecurityFilter.java:234) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (TrustedApplicationsFilter.java:100) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (BaseLoginFilter.java:169) (JiraLoginFilter.java:70) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (IteratingFilterChain.java:46) (DelegatingPluginFilter.java:66) (OAuthFilter.java:61) (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66)
	at com.atlassian.plugins.rest.module.servlet.RestSeraphFilter.doFilter(RestSeraphFilter.java:40)  <+3> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66)
	at com.atlassian.prettyurls.filter.PrettyUrlsCombinedMatchDispatcherFilter.doFilter(PrettyUrlsCombinedMatchDispatcherFilter.java:61)  <+9> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (ServletFilterModuleContainerFilter.java:77) (ServletFilterModuleContainerFilter.java:63) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (AbstractJohnsonFilter.java:71) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210)
	at org.tuckey.web.filters.urlrewrite.RuleChain.handleRewrite(RuleChain.java:176)
	at org.tuckey.web.filters.urlrewrite.RuleChain.doRules(RuleChain.java:145)
	at org.tuckey.web.filters.urlrewrite.UrlRewriter.processRequest(UrlRewriter.java:92)  <+10> (UrlRewriteFilter.java:394) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (GzipFilter.java:80) (GzipFilter.java:51) (JiraGzipFilter.java:55) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (IteratingFilterChain.java:46) (DelegatingPluginFilter.java:66)
	at com.atlassian.fastdev.AutoReloadFilter.doFilter(AutoReloadFilter.java:63)  <+3> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (DelegatingPluginFilter.java:66)
	at com.atlassian.prettyurls.filter.PrettyUrlsCombinedMatchDispatcherFilter.doFilter(PrettyUrlsCombinedMatchDispatcherFilter.java:61)  <+40> (DelegatingPluginFilter.java:74) (IteratingFilterChain.java:42) (ServletFilterModuleContainerFilter.java:77) (ServletFilterModuleContainerFilter.java:63) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (ChainedFilterStepRunner.java:87) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (AbstractCachingFilter.java:33) (AbstractHttpFilter.java:31) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (AbstractEncodingFilter.java:41) (AbstractHttpFilter.java:31) (PathMatchingEncodingFilter.java:45) (AbstractHttpFilter.java:31) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (JiraStartupChecklistFilter.java:78) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (MultipartBoundaryCheckFilter.java:41) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (ChainedFilterStepRunner.java:87) (JiraFirstFilter.java:57) (ApplicationFilterChain.java:243) (ApplicationFilterChain.java:210) (StandardWrapperValve.java:222) (StandardContextValve.java:123) (AuthenticatorBase.java:472) (StandardHostValve.java:171) (ErrorReportValve.java:99) (AccessLogValve.java:953) (StandardEngineValve.java:118) (CoyoteAdapter.java:408) (AbstractHttp11Processor.java:1008) (AbstractProtocol.java:589) (JIoEndpoint.java:310)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:744)
Caused by: com.atlassian.gadgets.GadgetParsingException: org.apache.shindig.gadgets.GadgetException: Unable to retrieve gadget xml. HTTP error 504
	at com.atlassian.gadgets.renderer.internal.GadgetSpecFactoryImpl.getGadgetSpec(GadgetSpecFactoryImpl.java:169)
	at com.atlassian.gadgets.renderer.internal.GadgetSpecFactoryImpl.getGadgetSpec(GadgetSpecFactoryImpl.java:86)
	at sun.reflect.GeneratedMethodAccessor326.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.doInvoke(ServiceInvoker.java:58)
	at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.invoke(ServiceInvoker.java:62)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
	at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invokeUnprivileged(ServiceTCCLInterceptor.java:56)
	at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invoke(ServiceTCCLInterceptor.java:39)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.osgi.service.importer.support.LocalBundleContextAdvice.invoke(LocalBundleContextAdvice.java:59)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
	at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
	at com.sun.proxy.$Proxy2646.getGadgetSpec(Unknown Source)
	at com.atlassian.gadgets.directory.internal.impl.AbstractDirectoryEntryProvider.getGadgetSpec(AbstractDirectoryEntryProvider.java:92)
	at com.atlassian.gadgets.directory.internal.impl.ConfigurableExternalGadgetSpecDirectoryEntryProvider.validateGadgetSpec(ConfigurableExternalGadgetSpecDirectoryEntryProvider.java:130)
	... 219 more
Caused by: org.apache.shindig.gadgets.GadgetException: Unable to retrieve gadget xml. HTTP error 504
	at org.apache.shindig.gadgets.DefaultGadgetSpecFactory.fetchObjectAndCache(DefaultGadgetSpecFactory.java:127)
	at org.apache.shindig.gadgets.DefaultGadgetSpecFactory.getGadgetSpec(DefaultGadgetSpecFactory.java:90)
	at com.atlassian.gadgets.renderer.internal.local.LocalGadgetSpecFactory.getGadgetSpec(LocalGadgetSpecFactory.java:82)
	at com.atlassian.gadgets.renderer.internal.local.LocalGadgetSpecFactory.getGadgetSpec(LocalGadgetSpecFactory.java:64)
	at com.atlassian.gadgets.renderer.internal.GadgetSpecFactoryImpl.getGadgetSpec(GadgetSpecFactoryImpl.java:140)