service-manager virtual

alpine-base presently hard depends on openrc. This makes it difficult to use alpine-base in settings where one either does not wish to use OpenRC or does not need a service manager at all, such as in a Docker container.

Proposed solution

Introduce a service-manager virtual, with openrc providing the highest provides_priority for the service-manager virtual and then make alpine-base depend on the service-manager virtual.

Other service managers can then also provide the service-manager virtual, such as main/s6-rc and testing/dinit. To be absolutely clear, this request does not involve the endorsement of any specific service-manager implementation presently in Alpine or proposed for future inclusion in Alpine.

Additionally, it is proposed to add a service-manager-none package which provides the service-manager virtual. This can be used for situations where a service manager is not required such as in a Docker container.

Benefits to Alpine

Experimentation with alternative service managers

Some users wish to experiment with alternative service managers, such as main/s6-rc and testing/dinit, as well as service managers that have not yet been packaged in Alpine. By virtualizing the service manager, it allows for simplified experimentation with service managers while not conflicting with alpine-base. Additionally, downstream consumers of Alpine can also experiment with different service managers.

Simplification of Alpine Docker image

Presently the Alpine Docker image attempts to equate alpine-base without openrc. If the service-manager virtual is implemented, then the /etc/apk/world for the Docker image could simply become:

alpine-base
service-manager-none

Configurability of service manager preference

A key mantra in Alpine is that everything should ultimately be configurable. By making the service manager preference configurable, it brings the service manager preference into alignment with this mantra.