+ [main] service: handles posting, comments, votes, ...

+ [auth] service: handles authentication users' requests (e.g.: using oauth 2)

Every time [main] receives a requests, it forwards the auth creds to the [auth] service for authentication.

When you generate the [main]:

+ server api config: will contain the api for the requests [main] receives (e.g.: post, upvote, ...)

+ client api config: will contain the api for the [auth] service since the [main] will be a client for the [auth] server

Another example would be a backend service that needs to pull data from third-party services (e.g.: instagram api, twitter api, ...). In that case the client api config will contain the api for those third-party services.

This tutorial explains in depth the config file's structure: https://github.com/vangav/vos_backend/blob/master/README/04_...

Instagram test example [https://github.com/vangav/vos_instagram_test] utilizes client api by including the client apis for the main and dash board services to test them. Check the service's generator config @ https://github.com/vangav/vos_instagram_test/tree/master/gen...

Please let me know if you have any more questions or need help using it :))