I found out recently that people too often think about microservices in context of broader solution like it would be one app, just scattered around. I did that mistake in the past, either. The longer I work with microservices the clearer it is to me that teams implementing them should forget about the big product, just focus on the service, as it would be product itself. Assume that anyone can use it, for any purpose they like, as long as they stick to the contract that is, and you'll be fine.

I tend to have two layers of design, now. One - big picture, which treats services anonymously. Just black boxes that respond to input. The goal here is to build solution like kids are building stuff from building blocks.

Other layer depicts services, as separate beings. They treat all their clients anonymously. They have a contract to fulfill and whomever plays by the rules can be served all right. They should be treated as completely separate projects, have their own backlog, release strategies, etc.

Now, if you would have a product that utilize certain data, would you allow some anonymous guy from the internet tap to it directly? No need to answer, I guess.

Edit: typo