This is the private fork of Ambari maintained by Cosmos to apply a (small) set of patches to the vanilla distribution.
You can check the differences between cosmos-ambari and the original ambari repo by using git diff:
git remote add ambari https://github.com/apache/ambari
git fetch ambari
git diff origin/<branch> ambari/trunk
From the project root:
mvn -B clean install package rpm:rpm -DskipTests -Dpython.ver="python >= 2.6" -Preplaceurl
For a guide see CUSTOM_AMBARI_SERVICE.rst