Review What to Check when upgrade / downgrade seems to be stuck? when it is published.
Meanwhile, are you able to click on 'Upgrade in Process'? apart from reviewing the ambari-server log, try the following URL's to find whats happening:
Use Ambari URL's to find what are the failures
This would show all the upgrade or downgrade attempts. for eg if this is a upgrade failure, identify the latest Upgrade attempt number
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.
Take a look at this article, https://community.hortonworks.com/articles/29499/ambari-troubleshooting-a-rolling-or-express-upgrad....
It has instructions on what to query and how to fix it. If you still need help, please include the results of the DB queries.
SELECT version, state FROM cluster_version cv JOIN repo_version rv ON cv.repo_version_id = rv.repo_version_id ORDER BY version DESC; -- Find how many hosts are in each state SELECT version, state, COUNT(*) FROM host_version hv JOIN repo_version rv ON hv.repo_version_id = rv.repo_version_id GROUP BY version, state ORDER BY version DESC, state;