What is a "good" architecture?

Hopefully you recognise it when you see it...

I believe every system has an architecture, documented or not, and intended or not. So I think it is reasonable to discuss if the architecture of a system is good or not, and that the question if the architecture description is good is a different, but related question.

So what criteria could you use to establish if an architecture is good? Is it suitable for it's purpose is a more precise question? But this probably differs depending on the stakeholder, a system could be very nice and intuitive for the user, but very difficult to develop and maintain for the developers. In the rest of this blog post I will writing about goodness from a developer perspective (including the architect, if one is involved).

I think there are different levels of how well the architecture suits it's purpose to guide and control the implementation.

The ideal level is where the developer understands the architecture and following the architecture is the obvious way to implement something. Doing it differently is seen as more difficult and less elegant.

The next level is where the developer understands the architecture, is able to follow it on her own and can evaluate if the implementation follows the architecture or not. The developer also understands the "debt" that would occur if she deviates from the architecture, for example in terms of compromising some quality attributes. At both this and the previous level the developer can contribute to the design of the architecture itself, and an appointed architect doing the design may not always be necessary.

The developer may need continuous support from the architect to be able to understand the architecture when working. This is very common and requires more work and puts limits on the the ratio between the number of architects and developers in large projects.

The worst level is where the developer cannot understand the architecture and the only one that can determine if the implementation follows the architecture is the architect by reviews. This is very work intensive on the part of the architect. The architect is also viewed as a police that interferes with the developers rather than supporting them.

I have worked at all this four levels in various projects, and I think that you need to be on the upper two if you talk about a good architecture from a developer perspective. I also think that if you want to be truly agile in a self-organising team it is at the two top levels you nee to be.
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