Validate parent-child relationship in async step

[norshtein]

Close #589

[jeremyrickard]

This change will likely break how things work with Kubernetes. Please do not merge it until we can discuss more.

[jeremyrickard]

This was done to support the way things can be done with Kubernetes. Take a Helm chart that may declare both a parent and child instance. When these are created, Kubernetes via Service Catalog will make the request for both resources, but there isn't a way to constrain the order. Therefore, you could get the child before the parent. In this scenario, the change you've introduced would cause things to end up in a failure state.

[norshtein]

Got that. Thanks for the explanation!

[zhongyi-zhang]

Extending ParentServiceID to a set of IDs should be done before this change. Or, it would break the sql-dbms-registered service which was recently checked in. See catalog:
https://github.com/Azure/open-service-broker-azure/blob/master/pkg/services/mssql/catalog.go#L374
https://github.com/Azure/open-service-broker-azure/blob/master/pkg/services/mssql/catalog.go#L323
BTW, I think ChildServiceID can be minimized to a simple bool to identity whether it is a parent service.

[norshtein]

Agree we should extend ParentServiceID to a set because registered services make parent-child relationship become a many-to-many relationship.
One question: do we really need a simple bool to identity whether it is a parent service? Anywhere this bool is used?

[zhongyi-zhang]

@norshtein here: https://github.com/Azure/open-service-broker-azure/blob/master/pkg/service/schema.go#L544. The alias is appended to provisioning parameters if it is a parent service.

[norshtein]

Thanks for pointing it out!