CAF::Service: Providing restart-if-running (conditional restart) functionality.

[jrha]

Rather than components having to handle this individually, see quattor/configuration-modules-core#1167 for example.

[stdweird]

if it is not implemented by the service, should we bother?
systemd has cond-restart, but i do not know how it handles sysvinit scripts.

[jrha]

Well indeed.

[gombasg]

Well-behaved SysV init scripts should also implement condrestart. The information about which service supports which action should live in OS-specific templates, not in the components. What CAF::Service could do is accept a mapping between requested actions to supported actions; template code could then describe that "well, you may only want to reload the configuration, but the version shipped by the OS only understands restart", or even things like "the restart action is known to be broken, do a distinct stop followed by a start instead".

[jrha]

Discussed at RAL workshop: agreed to add support for condrestart but not work around any lack of functionality for SysV init scripts - up to admins to understand if the underlying service support it or not.