Not possible to terminate inactive AWS instance. Currently we are having around 500 AWS instances as inactive nodes, which are not possible to be removed as they are already terminated on AWS side. See accordingly stacktrace when trying to terminate this:
Root cause:

com.amazonaws.AmazonServiceException: Status Code: 400, AWS Service: AmazonEC2, AWS Request ID: 2ec705ea-4b11-4aa2-a6c2-2ae47f11838e, AWS Error Code: InvalidInstanceID.NotFound, AWS Error Message: The instance ID 'i-a95a8beb' does not exist
at com.amazonaws.http.AmazonHttpClient.handleErrorResponse(AmazonHttpClient.java:798)
at com.amazonaws.http.AmazonHttpClient.executeHelper(AmazonHttpClient.java:421)
at com.amazonaws.http.AmazonHttpClient.execute(AmazonHttpClient.java:232)
at com.amazonaws.services.ec2.AmazonEC2Client.invoke(AmazonEC2Client.java:8711)
at com.amazonaws.services.ec2.AmazonEC2Client.terminateInstances(AmazonEC2Client.java:5410)
at com.pmease.quickbuild.plugin.cloud.ec2.EC2NodeLauncher.terminateNode(EC2NodeLauncher.java:238)
at com.pmease.quickbuild.web.page.grid.InactiveNodesPanel$2$2$1.onClick(InactiveNodesPanel.java:127)
at org.apache.wicket.markup.html.link.Link.onLinkClicked(Link.java:187)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.wicket.RequestListenerInterface.internalInvoke(RequestListenerInterface.java:272)
at org.apache.wicket.RequestListenerInterface.invoke(RequestListenerInterface.java:220)
at org.apache.wicket.request.handler.ListenerInterfaceRequestHandler.invokeListener(ListenerInterfaceRequestHandler.java:179)
at org.apache.wicket.request.handler.ListenerInterfaceRequestHandler.respond(ListenerInterfaceRequestHandler.java:165)
at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:719)
at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:63)
at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:210)
at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:253)
at org.apache.wicket.protocol.http.WicketFilter.processRequest(WicketFilter.java:162)
at org.apache.wicket.protocol.http.WicketServlet.doGet(WicketServlet.java:137)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:734)
at com.pmease.quickbuild.web.MainServlet.service(MainServlet.java:124)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
at org.eclipse.equinox.http.helper.FilterServletAdaptor$FilterChainImpl.doFilter(FilterServletAdaptor.java:56)
at org.eclipse.jetty.servlets.UserAgentFilter.doFilter(UserAgentFilter.java:82)
at org.eclipse.jetty.servlets.GzipFilter.doFilter(GzipFilter.java:243)
at org.eclipse.equinox.http.helper.FilterServletAdaptor.service(FilterServletAdaptor.java:37)
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:669)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1336)
at com.pmease.quickbuild.Quickbuild$DisableTraceFilter.doFilter(Quickbuild.java:1033)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1307)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:453)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:229)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1072)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:382)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1006)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:154)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
at org.eclipse.jetty.server.Server.handle(Server.java:365)
at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:485)
at org.eclipse.jetty.server.BlockingHttpConnection.handleRequest(BlockingHttpConnection.java:53)
at org.eclipse.jetty.server.AbstractHttpConnection.headerComplete(AbstractHttpConnection.java:926)
at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.headerComplete(AbstractHttpConnection.java:988)
at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:635)
at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:235)
at org.eclipse.jetty.server.BlockingHttpConnection.handle(BlockingHttpConnection.java:72)
at org.eclipse.jetty.server.bio.SocketConnector$ConnectorEndPoint.run(SocketConnector.java:264)
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:608)
at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:543)
at java.lang.Thread.run(Unknown Source)


Complete stack:

org.apache.wicket.WicketRuntimeException: Method onLinkClicked of interface org.apache.wicket.markup.html.link.ILinkListener targeted at [ [Component id = item]] on component [ [Component id = item]] threw an exception
at org.apache.wicket.RequestListenerInterface.internalInvoke(RequestListenerInterface.java:282)
at org.apache.wicket.RequestListenerInterface.invoke(RequestListenerInterface.java:220)
at org.apache.wicket.request.handler.ListenerInterfaceRequestHandler.invokeListener(ListenerInterfaceRequestHandler.java:179)
at org.apache.wicket.request.handler.ListenerInterfaceRequestHandler.respond(ListenerInterfaceRequestHandler.java:165)
at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:719)
at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:63)
at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:210)
at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:253)
at org.apache.wicket.protocol.http.WicketFilter.processRequest(WicketFilter.java:162)

java.lang.reflect.InvocationTargetException
at sun.reflect.GeneratedMethodAccessor586.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.wicket.RequestListenerInterface.internalInvoke(RequestListenerInterface.java:272)
at org.apache.wicket.RequestListenerInterface.invoke(RequestListenerInterface.java:220)
at org.apache.wicket.request.handler.ListenerInterfaceRequestHandler.invokeListener(ListenerInterfaceRequestHandler.java:179)
at org.apache.wicket.request.handler.ListenerInterfaceRequestHandler.respond(ListenerInterfaceRequestHandler.java:165)
at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:719)
at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:63)
at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:210)
at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:253)
at org.apache.wicket.protocol.http.WicketFilter.processRequest(WicketFilter.java:162)