Declaring a dependency between services (require)

A service can require another to be enabled on the same host. The dependency is declared in the dnf/config/modules.nix registry, not in the module itself.

dnf/config/modules.nix

monitoring = {
  require = [ "prometheus" ];
};

The generator validates the rule: enabling monitoring on a host that does not have prometheus causes the generation to fail (with an explicit message). This is a consistency safeguard, not an automatic activation: the administrator must declare both services.

Why not automatic activation?

Declaring both services makes the intent explicit and allows the generator to produce the DNS and reverse proxy entries for the dependency. Implicit activation on the Nix side would leave these artifacts missing.

Multiple dependencies

require is a list: require = [ "prometheus" "postfix" ];. Each entry must be a service declared in the registry.