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You have applied either the Client-side Service Discovery pattern or the Server-side Service Discovery pattern. Service instances must be registered with the service registry on startup so that they can be discovered and unregistered on shutdown.
How are service instances registered with and unregistered from the service registry?
A 3rd party registrar is responsible for registering and unregistering a service instance with the service registry. When the service instance starts up, the registrar registers the service instance with the service registry. When the service instance shuts downs, the registrar unregisters the service instance from the service registry.
Examples of the 3rd Party Registration pattern include:
The benefits of the 3rd Party Registration pattern include:
There are also some drawbacks:
The 3rd party registrar might only have superficial knowledge of the state of the service instance, e.g. RUNNING or NOT RUNNING and so might not know whether it can handle requests. However, as mentioned above some registrars such as Netflix Prana perform a health check in order to determine the availability of the service instance.
Unless the registrar is part of the infrastructure it’s another component that must be installed, configured and maintained. Also, since it’s a critical system component it needs to be highly available.