Agent is unable to connect to JBoss ON server because initialization callback is failing due to a network connection failure

Issue

• Agent not starting cleanly

• The agent fails to connect to the server and the following message is logged:

  ERROR [RHQ Server Polling Thread] (enterprise.communications.command.client.JBossRemotingRemoteCommunicator)- {JBossRemotingRemoteCommunicator.init-callback-failed}The initialize callback has failed. It will be tried again. Cause: org.jboss.remoting.CannotConnectException:Can not connect http client invoker. Connection timed out. -> java.net.ConnectException:Connection timed out
  org.jboss.remoting.CannotConnectException: Can not connect http client invoker. Connection timed out.
  

• Agent log contains the following warning:

  WARN  [RHQ Server Polling Thread] (org.rhq.enterprise.agent.FailoverFailureCallback)- {AgentMain.too-many-failover-attempts}Too many failover attempts have been made [1]. Exception that triggered the failover: [org.jboss.remoting.CannotConnectException: Can not connect http client invoker. Connection timed out.]
  

• Agent can not connect to server if it is unable to resolve the server's end-point address

• I have installed JON and RHQ-Agents. All Agents were available in JON console when I had last logged in to JON. Now, all Agent appear unavailable though they are up and running

• Agent fails to connect to the server with the following error message:

  ... ERROR [RHQ Server Polling Thread] (enterprise.communications.command.client.JBossRemotingRemoteCommunicator)- {JBossRemotingRemoteCommunicator.init-callback-failed}The initialize callback has failed. It will be tried again. Cause: org.jboss.remoting.CannotConnectException:Can not connect http client invoker after 1 attempt(s) -> java.net.ConnectException:Connection refused (Connection refused)
  org.jboss.remoting.CannotConnectException: Can not connect http client invoker after 1 attempt(s)
  ...
  Caused by: java.net.ConnectException: Connection refused (Connection refused)
  ...