Systemd
Packages containing systemd unit files need to use scriptlets to ensure proper handling of those services. Services can either be enabled or disabled by default. To determine which case your specific service falls into, please refer to FESCo's policy here: Packaging:DefaultServices. On upgrade, a package may only restart a service if it is running; it may not start it if it is off. Also, the service may not enable itself if it is currently disabled.
New Packages
In this context, a new package is a package which has never included a SysV initscript.
Scriptlets
The systemd package provides a set of helper macros to handle systemd scriptlet operations. These macros support systemd "presets", as documented in Features/PackagePresets. The %systemd_requires macro is a shortcut for listing the per-scriptlet dependencies on systemd.
%{?systemd_requires}
BuildRequires: systemd
[...]
%post
%systemd_post apache-httpd.service
%preun
%systemd_preun apache-httpd.service
%postun
%systemd_postun_with_restart apache-httpd.service
Some services do not support being restarted (e.g. D-Bus and various storage daemons). If your service should not be restarted upon upgrade, then use the following %postun scriptlet instead of the one shown above:
%postun %systemd_postun apache-httpd.service
If your package includes one or more systemd units that need to be enabled by default on package installation, they must be covered by the Fedora preset policy.
For details on what these macros evaluate to, refer to the following sources:
https://github.com/systemd/systemd/blob/master/src/core/macros.systemd.in,
https://github.com/systemd/systemd/blob/master/src/core/triggers.systemd.in and
http://www.freedesktop.org/software/systemd/man/daemon.html.