System Design Description Overview
This System provides the database, which stores information related to the currently actively offered Services within the Local Cloud.
The purpose of this System is therefore to allow:
- Application Systems to register what Services they offer at the moment, making this announcement available to other Application Systems on the network.
- They are also allowed to remove or update their entries when it is necessary.
- All Application Systems can utilize the lookup functionality of the Registry to find Public Core System Service offerings in the network, otherwise the Orchestrator has to be used.
However, it is worth noting, that within this generation the lookup functionality of Services is integrated within the “orchestration process”. Therefore, in the primary scenario, when an Application System is looking for a Service to consume, it shall ask the Orchestrator System via the Orchestration Service to locate one or more suitable Service Providers and help establish the connection based on metadata submitted in the request. Direct lookups from Application Systems within the network is not advised in this generation, due to security reasons.
However, the lookup of other Application Systems and Services directly is not within the primary use, since access will not be given without the Authorization JWT (JSON Web Token). The use of the TokenGeneration is restricted to the Orchestrator for general System accountability reasons.
This System only provides one Core Service the Service Discovery
There are two use case scenarios connected to the Service Registry.
- Service registration, de-registration
- Service Registry querying (lookup)
The register method is used to register services. The services will contain various metadata as well as a physical endpoint. The various parameters are representing the endpoint information that should be registered.
The unregister method is used to unregister service instances that were previously registered in the Registry. The instance parameter is representing the endpoint information that should be removed.
The query method is used to find and translate a symbolic service name into a physical endpoint, for example an IP address and a port. The query parameter is used to request a subset of all the registered services fulfilling the demand of the user of the service. The returned listing contains service endpoints that have been fulfilling the query.
There is another functionality that does not bound to any Services, just an internal part of the Service Registry. There are two optional cleanup tasks within the Service Registry, which can be used to remove old, inactive service offerings. The first task is based on pinging the service provider and if the provider does not respond to the ping, its offered services will be deleted. The second task is based on a feature, called “Time to Live”. Service providers upon registration can provide a timestamp called “end_of_validity” number, which specifies how long the service will be offered by the provider, making the service de-registrations unnecessary, if this task is active. The task is used to remove expired services. The third task is using a feature called “Heartbeat” (Not yet implemented), where the Service provider periodically signals to the Service Registry that it is still alive. When it misses it will be removed. All of these internal tasks can be configured in the application.properties file.
This System can be secured via the HTTPS protocol. If it is started in secure mode, it verifies whether the Application System possesses a proper X.509 identity certificate and whether that certificate is Arrowhead compliant in its making. This certificate structure and creation guidelines ensure:
- Application System is properly bootstrapped into the Local Cloud
- The Application System indeed belongs to this Local Cloud
- The Application System then automatically has the right to register its Services in the Registry.
If these criteria are met, the Application System’s registration or removal message is processed. An Application System can only delete or alter entries that contain the Application System as the Service Provider in the entry.
- ServiceRegistry v4.6.0: https://github.com/eclipse-arrowhead/core-java-spring#serviceregistry