So what would be a good architecture? How would I recognize it if I stumbled against it?

My own inclinations here are that it would be good to have as few different technologies as possible. To run things on as few different machines as possible and to have automated tests for everything. The thing is that as soon as there are multiple technologies you get to have different people specializing in them and it is always the communications between those that becomes painful. The automated tests are there to prevent fear of change setting in. I think I am kind of advocating what is called a 'big ball of mud' but that I want it to be a transparent ball of mud because of automated testing. I guess what I am saying is that I distrust most developments in so-called application architecture of the last few decades except automated tests. In particular, I think frameworks and microservices are mostly just bad.

In an existing system some combination of these attributes:

- High quality (e.g. low number of issues hit by customers, resilient to failures, efficient, secure etc.)

- Easy to maintain (well organized, broken down in a sensible way into components or layers)

- Easy to extend/adapt to future requirements (i.e. the designer was able to anticipate the likely direction of the system and account for that in the design)

Automated testing feels a bit orthogonal to me but a system that is easy to test is likely one with a better architecture. It's not strictly part of what I'd call architecture.

Less different technologies - YES!

Runs on fewer machines is a sign of an efficient/performant design. Less well designed systems exhibit bloat that is often made up for by running on more machines.

Good architecture reduces cost, while still achieving business goals.

(E.g. If you have problems hiring for a weird stack, it increases hiring cost; you have problems with dependency zoo maintenance it increases costs; if it took a year to build a framework that could've been a bash script, it increased the cost)

Every other architecture “metric” should be useful/convenient proxy towards reducing overall cost.

I like to ask this question: "Can I make this system do what I need it to do while being able to stay with the existing architecture or do I need to become a special case?"

There is a lot buried in this question but it can help sus out if the rules in place allow the challenges the system faces today or if it is antiquated in how it views the world it operates in. Good and bad can be related to time and context but like many things in software, it needs to be able to change and sometimes that change requires the willingness to start from scratch with new assumptions.

Attributes like mix of languages, system/task ownership, specialization are symptoms that an architecture may want to enable or discourage but are symptoms, not measures of quality. Automated testing and how much that influences your software design is more aligned with the culture of the organization and how it treats code than it is the arrangement of subsystems it is built on.

I've been doing this stuff for about 15 years now. Longer than many, not as long as some.

In my opinion, good architecture should be easy to extend, easy to scale (up and down), easy to reproduce. Microservice architectures are easy to scale, but usually hard to reproduce (any amount of config per service adds up a lot) and can be very hard to extend too (any changes to one service might ripple to many others, with knock-on effects)

One of my biggest red flags for a bad architecture is if you cannot easily create a (preferably localhost) development environment for it. I think this is where a lot of microservice based projects stumble. It leads to a lot of brittleness and a very siloed development team in my experience. Replacing what should be a library call or DB query with a network request to another service (which then has to query the DB for you) is a certain kind of lunacy.

Frameworks that are very opinionated are also very bad in my opinion. Depending how strict they are if you're doing anything even remotely unexpected you will butt up against the limitations of the framework often. That's annoying to me, I prefer to build my own stuff.