Scalability and stability.
You need to process more requests? Launch more virtual machines, easy.
Your microservice is a shit and it crashes every second? Don't care, it will be relaunched automatically.
Companies that repeatedly fail to detect and solve this type of problem using automated testing and QA are exactly the companies that lack the sophistication to do distributed microservice architecture.
Learn to do proper CI/CD, end-to-end testing, and logging/metrics on your monolith before you decide to transition to microservices.
Also in many cases work should not be performed synchronously in response to http requests but in a background queue to keep your service robust and responsive. When taking a new order you should just place it in some queue and respond ASAP so there is zero chance you miss a customer order because of some error. In that case there is no difference in scaling a monolith or microservice as you can indepedently deploy 25 consumers for module X events or 10 consumers for module Y events and so on.
At a (potentially much) bigger cost.
For big companies it might me a miniscule difference, but for smaller companies it can be a deal-breaker.
Running costs.
> Having all the code in one place _can_ make things easier to figure out in the long term.
My experience is the exact opposite. A huge monolith makes it harder for developers - especially new ones - to get a grasp of how everything is connected. A separation of concern into micro services is sometimes a good solution.
Sir this is HN, half of the people here will quit their team well before maintainability is even uttered.
If you refer to databases: Splitting one service into two services can at most give you a 2x scale-up potential (usually a lot less), and the effect diminishes for 3th, 4th service. Mathematically and logically. Splitting services = vertical scaling.
If you want 100x, 1000x scaling you need to invest in true horizontal scaling anyway, and that works pretty much the same way for monoliths as microservices.
Few extra?
Have you not considered applications where you need to spin up/down _extremely_ resource intensive instances?
A year++ ago I worked on a health-related application which used a system for processing X-ray images. During typical work hour (6 am-6 pm) it required a _huge_ amount of CPU and RAM instances. By shifting those specific services out to specialised instanced, we saw a $50K/month saving.
The rest of the application is a lot more lightweight, but of course has to run 24/7, but being able to spin up/down required instances, and just pay for what you use, is a huge benefit for a lot of companies and organisations.
I maintain a SaaS written as a monolith and I can absolutely spin instances that only load one part of the code and do a single thing, for example some instances only handle MQTT messages while others only serve HTTP endpoints. That does not make it microservices, it is all one code base sharing one database.
It has become more and more true each passing year.
This "microservices are better" argument was made in the 90ies and top dog is still Linux kernel (the one that was on the monolith side of that debate).
So yeah - microservice advocates haven't learned anything since the 90ies, or from the SOA era, etc... (but I suspect they were in secondary/high school then)
An anecdote: When I joined my current company had more code to orchestrate services, than the actual business value generating code in the services. We still produce an inordinate amount of code that exists just to facilitate microservice architecture. (it's also untested code, because we just don't have the money to spend time on testing it)
> I can hardly understand folks running k8s for a 3-container setup.
Why can't you understand them? I understand them - It's cool, that's why they run it. It's not about rational use of resources, it's about being cool.
Regarding your point, most other disciplines gain knowledge over time, such as civil engineering, chemistry or biology and we don't discard results from the past with this kind of strawman argument of there supposedly not being anything to learn since. If things were like that, any progress would be impossible.
This attitude is extremely toxic to the development community.
"Its old" is NOT valid criticism.
"Its new" is NOT valid praise.