Confirm the repository is configured by checking the repo list
yum repolist
You should see the Ambari and HDP utilities repositories in the list
repo id repo name | AMBARI-1.x | Ambari 1.x | HDP-UTILS-1.1.0.16 | Hortonworks Data Platform Utils
Install the Ambari bits using yum. This also installs PostgreSQL:
yum install ambari-server
