IME mixing financial concerns with engineering concerns puts you into an architectural corner. Suddenly the business wants an integration between the two projects - which cluster does the integration run on? Do you spin up a whole new cluster / account just for the integration? Inside a project, you need to run dedicated infrastructure for large customers. How do you report that for billing?
Just set up tagging correctly.
> For very small projects, one cluster per product is expensive, so mutualisation makes sense.
If you're not working for a BigCo, every project starts out very small ;) You shouldn't optimize prematurely.
About integration, I do not understand what you say You have a provider and a consumer, each of them build (and pay) their own parts
If service A is in one cluster, and service B is in another cluster, where billing is per-cluster, in which cluster do you put the ETL integration? It belongs to either both or neither, depending on how Finance wants to bill it.
Easier to manage because less dependencies : you are the sole user, so you can do whatever you want
This is the greatness of public cloud, where multi team synchronisation can be reduced a lot
For very small projects, one cluster per product is expensive, so mutualisation makes sense. Past a certain size, this is not the case