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.
modules
package, with no dependencies on Cortex. For ex: Remove code from Loki that was copied from pkg/cortex/cortex.go
.To make the modules package extensible, we need to abstract away any Cortex specific details from the module manager. The proposed design is to:
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 pkg/util/modules
. 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 modules.Manager
using RegisterModule
. The parameters are:
name
: Name of the moduleinitFn
: A function that will be used to start the module. If it returns nil, and other modules depend on it, InitModuleServices
will return an error.Dependencies between modules can be added using AddDependency
. The parameters to the function are:
name
: Name of the moduledependsOn
: A variadic list of modules that the module depends on.These need to be added before the call to InitModuleServices
.
The application can be initialized by running initFn
's of all the modules in the right order of dependencies by invoking InitModuleServices
with the target module name.
pkg/cortex
: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 Cortex.New()
function, InitModuleServices
should be part of Cortex.Run()
and to enable this, modules.Manager
would be made a member of the Cortex
struct.
Following these changes, the Modules package will be a generic dependency management framework that can be used by any project.
pkg/util/modules
package, and initialize a new instance of the Manager
using modules.NewManager()
pkg/util/services
).Manager.RegisterModule()
by passing name of the module and initFn
for the module.Manager.AddDependency()
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.Manager
outside of the Cortex struct.