The Service Locator pattern is actually an anti-pattern. It's not considered a good practice because it adds much more complexity to an ecosystem. The pattern consists of a central registry, called a Service Locator, where services register their abilities, and other services can consult the registry and know where the services they need are located:

The Service Locator is similar to the Front Controller, but with added complexity, as you need to contact the Service Locator and the service you need, instead of just making a simple request to a Front Controller.