alt Hacker NewsYou need multiple services whenever the scaling requirements of two components of your system are significantly different. That's pretty much it. These are often called micro services, but they don't have to actually be "micro"
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Another case I’ve seen is to separate a specific part of the system which has regulatory or compliance requirements that might be challenging to support for the rest of the larger system, eg HIPAA compliance, PCI compliance, etc.
(To clarify, I’m not disagreeing with you!)
It has other advantages.
Operationally, it is very nice to be able to update one discrete function on its own in a patch cycle. You can try to persuade yourself you will pull it off with a modular monolith but the physical isolation of separate services provides guarantees that no amount of testing / review / good intentions can.
However, it's equally an argument for SOA as it is for microservices.
I came here to say the same. If you’re arguing either for or against microservices you’re probably not thinking about the problem correctly. Running one big service may make sense if your resource needs are pretty uniform. Even if they’re not you need to weight the cost of adding complexity vs the cost of scaling some things prematurely or unnecessarily. Often this is an acceptable precursor to splitting up a process.
That's the most nonsensical reason to adopt microservices imo.
Consider this: every API call (or function call) in your application has different scaling requirements. Every LOC in your application has different scaling requirements. What difference does it make whether you scale it all "together" as a monolith or separately? One step further, I'd argue it's better to scale everything together because the total breathing room available to any one function experiencing unusual load is higher than if you deployed everything separately. Not to mention intra- and inter-process comm being much cheaper than network calls.
The "correct" reasons for going microservices are exclusively human -- walling off too much complexity for one person or one team to grapple with. Some hypothetical big brain alien species would draw the line between microservices at completely different levels of complexity.