Cross-service linking for HATEOAS micro-services

Question

I have a number of micro-services built with Spring Boot, so for a bit of fun, I thought I'd have a go at adding HATEOAS to them to help set up cross-resource linking. It seems to work quite nicely within a particular project, but I was wondering whether there's a good way to link across APIs. As an example, imagine I have 3 services:

A user details service: Code:

/users/{userid}

A user calendar service: Code:

/users/{userid}/appointments
/users/{userid}/appointments/{appointmentid}

A user messaging service: Code:

/users/{userid}/messages
/users/{userid}/messages/{messageid}

To make this browsable via the API, it would be good to have links from a user resource to its appointments and messages. Similarly, it would be nice to have links back from those resources. This is all very achievable when I have a single API with everything on the classpath, where I can write code such as:

Code:

user.add(linkTo(methodOn(CalendarController.class).appointments(user.getKey())).withRel("appointments"))

However I'm not able to do this if CalendarController is not on the classpath of the service I'm currently hitting.

Is there a good/recommended method for creating links to controllers which are not in the current project?

Referenced from spring forums

Answer 1

Maybe this is a bit more involved than you were hoping, but as mentioned here, this is exactly what Eureka is for. It also has really nice integration with the new Spring Cloud project.