I found the exact problem...my cluster has 4 nodes. and this error happened today to the namenode! Because of this, the entire cluster is kind of down...
I'm searching for help on how to replace the dead namenode but that almost seems impossible. Any one could help?
I was not able to solve the issue and finally decide to reinstall ambari that remove the problem. I didn't face the same kind of issue since then.
I faced this issue of Ambari Heartbeat loss after a network IP change on the Cent OS 7 VM. this was due to some network issue in my area. (cant escape it).
Therefore Ambari server got the heartbeat issue, I tried all the options (suggested in the above posts) of Ambari Agent config file IP check, hosts file IP check and then Ambari agent and Server services restart etc. But nothing worked, in the end I had to delete the VM and recreate a fresh VM.
I have faced similar issue today and have lost the heartbeat for all of the services.
I have done just restarted the ambari agent , and relaunched and logined into Ambari and it worked well.
Please let me know in case of queries.