[throwaway894345]

Code quality is only one reason to use microservices; deployment frequency is another (you want people to be able to deploy their service without needing to coordinate with every other service in the system).

Moreover, code quality isn't just encumbered by junior devs--in fact, in my experience it's more often managers pressuring developers to take shortcuts (e.g., taking a dependency on another system's private internals in the name of expedience, while swearing up and down that we will totally clean it up in a future iteration) or other organizational hurdles that make it difficult/impossible to fix it the right way, so shortcuts are taken instead (with microservices, the organization has to confront those issues, they can't be easily papered over by bypassing official interfaces).

Another reason to prefer microservices is security--not putting every secret in a single process's memory space is a great way to minimize blast radius if a service is compromised.

Another reason is reliability--if one system has a catastrophic failure mode, it won't take out all other systems. Of course, if the failing system is a core service, then it may not matter, but at least you're not bringing everything down when some service on the architectural periphery goes haywire.

[jnash]

Nothing you say can't be accomplished by using libraries instead. The largest software on earth (Linux/Windows/...) is created by composing thousands of libraries into a single system. With thousands of developers contributing from all over the world. It works. It's proven.

[throwaway894345]

Composing libraries offers some of the advantages of microservices, but not all of them. For example, a vulnerable library still has access to all of the secrets used by any other library, whereas a vulnerable microservice will only yield the secrets it needs. Similarly, a critical bug in one library can bring the whole process down, even if the library itself is a non-critical component—a critical bug in a microservice will only tank that service (and maybe services that depend on it if they don’t degrade gracefully). Notably, Linux and Windows spend tremendous energy making sure these vulnerabilities and bugs don’t slip through!