First, this has nothing to do with microservices. Needing cloud infrastructure and building microservices are 2 orthogonal things.

Second, it has nothing to do with the tech you're using. MySQL is irrelevant. So is a monolithic backend.

What IS important is the security and infrasture behind the data your storing. Clinical data (and data captured in EMR's) is easily some of the most sensitive stuff you'll come across (unless you work in govt). The idea that I wouldn't use off-the-shelf, already-tested solutions specifically for this problem with a cloud provider is nuts. I pay Azure peanuts compared to what I'd have to pay a full-time person to manage multiple environments, security updates, provisioning new infra, etc. And that's not even considering the actual process you need to go to connect to outside systems.

Most integrations want you to have a SOCS audits and stuff. What happens when there is a breach? Do you have the personnel on staff to understand and troubleshoot the issue? Remember the "we have your data and will release it for bitcoin" hacks? That's only made possible by these systems sitting in closets in someone's facility.

And trust me, this isn't just a "large enterprisey" problem. It's a "everyone who wants to build an app in this space" problem.

So you can use MySql (if you can host it compliantly) and I'm building what you could theoretically call a "monolithic" backend and it's working well. I use MSSQL on Azure though.