Modules, not microservices
Microservices, while often sold as solving a technical problem, usually actually solve for a human problem in scaling up an organization.There's two technical problems that microservices purport to solve: modularization (separation of concerns, hiding implementation, document interface and all that good stuff) and scalability (being able to increase the amount of compute, memory and IO to the specific modules that need it).The first problem, modules, can be solved at the language level. Modules can do that job, and that's the point of this blog post.The second problem, scalability, is harder to solve at the language level in most languages outside those designed to be run in a distributed environment. But most people need it a lot less than they think. Normally the database is your bottleneck and if you keep your application server stateless, you can just run lots of them; the database can eventually be a bottleneck, but you can scale up databases a lot.The real reason that microservices may make sense is because they keep people honest around module boundaries. They make it much harder to retain access to persistent in-memory state, harder to navigate object graphs to take dependencies on things they shouldn't, harder to create PRs with complex changes on either side of a module boundary without a conversation about designing for change and future proofing. Code ownership by teams is something you need as an organization scales, if only to reduce the amount of context switching that developers need to do if treated as fully fungible; owning a service is more defensible than owning a module, since the team will own release schedules and quality gating.I'm not so positive on every microservice maintaining its own copy of state, potentially with its own separate data store. I think that usually adds more ongoing complexity in synchronization than it saves by isolating schemas. A better rule is for one service to own writes for a table, and other services can only read that table, and maybe even then not all columns or all non-owned tables. Problems with state synchronization are one of the most common failure modes in distributed applications, where queues get backed up, retries of "bad" events cause blockages and so on.