Cortex uses modules to start and operate services with dependencies. Inter-service dependencies are specified in a map and passed to a module manager which ensures that they are initialised in the right order of dependencies. While this works really well, the implementation is tied in specifically to the Cortex struct and is not flexible for use with other projects like Loki, which also require similar forms of dependency management.
We would like to extend modules in cortex to a generic dependency management framework, that can be used by any project with no ties to cortex.
modulespackage, with no dependencies on Cortex. For ex: Remove code from Loki that was copied from
To make the modules package extensible, we need to abstract away any Cortex specific details from the module manager. The proposed design is to:
Make a new component
Manager, which is envisioned to be a central manager for all modules of the application. It stores modules & dependencies, and will be housed under a new package
Manager has the following methods for interaction:
func (m *Manager) RegisterModule(name string, initFn func() (Service, error)) func (m *Manager) AddDependency(name string, dependsOn... string) error func (m *Manager) InitModuleServices(target string) (map[string]services.Service, error)
Modules can be created by the application and registered with
RegisterModule. The parameters are:
name: Name of the module
initFn: A function that will be used to start the module. If it returns nil, and other modules depend on it,
InitModuleServiceswill return an error.
Dependencies between modules can be added using
AddDependency. The parameters to the function are:
name: Name of the module
dependsOn: A variadic list of modules that the module depends on.
These need to be added before the call to
initFn’s of all the modules in the right order of dependencies by invoking
InitModuleServiceswith the target module name.
WrappedService present in the current
module design will be deprecated. All
initFn’s will be wrapped into
WrappedService by default.
While the process of loading modules into
modules.Manager should be remain as part of the
InitModuleServices should be part of
Cortex.Run() and to enable this,
modules.Manager would be made a member of the
Following these changes, the Modules package will be a generic dependency management framework that can be used by any project.
pkg/util/modulespackage, and initialize a new instance of the
Manager.RegisterModule()by passing name of the module and
initFnfor the module.
modules.Manager, initialize the application by calling
Manager.InitModuleServices()which initializes modules in the right order of dependencies.
Run()method to make it independent of Cortex. This will help reduce replicated code in the Loki project as well as help manage
modules.Manageroutside of the Cortex struct.