With recent improvements in Ambari, upgrading can be done easily either using Rolling Upgrade or Express Upgrade. But there are times when upgrade/downgrade gets stuck either since all the precautions were not followed or due to product issues. When upgrade gets stuck, it is typically in an Upgrade Paused status or there aren't any status as such. At this juncture, care needs to be taken to ensure that the ambari-server is not restarted without consulting with Technical Support.
Current status of the upgrade can be checked using multiple method:
Ambari Log files
Ambari API URL's
1. Ambari Log files
Review Ambari Log files for any errors / exception when the upgrade is in progress.
this would list all the actions taken as part of upgrade attempt 119.
Review the output to identify those JSON outputs without status 'COMPLETED'. This would give a clue to what items have failed to move to COMPLETED status and troubleshoot from there on.
3. Ambari Database
Note: Care has to be taken while using Ambari DB. It is mandatory to backup the database before doing any upgrade / downgrade. Following tables in the Ambari database are ideal to start troubleshooting the issues:
repo_version - this contains all the repo versions installed in the system