This is a solution for how you can exclude certain packages being updated when using yum-cron.
Docker and kernel are packages I would like to exclude from yum-cron.
The solution to this is to modify the /etc/yum/yum-cron.conf file adding this to the [base] section
exclude = kernel* docker*
On RHEL6/Centos6 you can use the YUM_PARAMETER to do the same thing
If you would like to exclude certain packages from yum alltogether you need to modify the affected yum repository.
Example to permanently exclude certain packages like Docker from being updated using the yum command/CLI
Add the following line under [rhel-7-server-extras-rpms]
exclude = docker*
Before adding a exclude command verify that you add the exclude line under the right repository.
# yum info docker
From repo : rhel-7-server-extras-rpms