A response to some reading materials

As part of my effort to get up to date with my skillset, I've joined the dev.to community (pointed out by Ali Spittel, who has written some very good pieces on medium.com). This morning I came across a piece from last year which I thought would be worth a read: 9 Software Architecture Interview Questions and Answers.

It started out fairly well:

A software architect is a software expert who makes high-level design choices and dictates technical standards, including software coding standards, tools, and platforms. Software architecture refers to the high level structures of a software system, the discipline of creating such structures, and the documentation of these structures.

I don't believe that the rest of the piece matches up to that initial paragraph. The first question was pretty good: What does "program to interfaces, not implementations" mean? The sting, though, was that theanswer dived straight into OO-speak, talking about factories.

I'm sure that's ok for somebody who has just finished their first single-semester class on Design Patterns, but doesn't help you in the real world - and surely your lecturer for that class would be keen to help you turn the theory into practice?

Cue #TheVoiceOfExperience!

When I was working as a tier-4 support engineer for Sun Microsystems, we had a support call from an (of course) irate customer when a recent kernel/libc patch had fixed a bug. I forget the details of the bug, but I do not forget what the customer insisted that we do. They demanded that we reverse the bugfix because their product depended upon the broken behaviour.

Many other customers, along with our test teams and engineering teams, had identified that this particular behaviour was a bug and needed to be fixed. Fixed so that our product behaved according to a particular published specification. Everybody apart from this irate customer wanted us to get the interface correct.

If I get asked a question along these lines, I answer that you cannot depend upon the implementation of any interface, because that's not sustainable for reliable software. If you depend upon particular behaviour from an implementation, then you are at the mercy of the implementor and that way lies increased costs. Don't do it. Or if you absolutely must (yes, there are times when that's the case), then do your utmost to ensure that you get a commitment from the implementation provider that they won't go and change things out from under you without warning. In the Solaris development model, this was a Contract and where we had them we adhered to them - rigorously.

The second question wasn't about Software Architecture at all:

Q2: What are the differences between continuous integration, continuous delivery, and continuous deployment?

The subhead even called that out as #DevOps!

This question is about engineering processes. If you want to turn it into a question which is closer to being about architecture, perhaps you could ask

Please describe your software development quality framework, and how you put it into practice.

Questions three, four and five were all about whether you could recall what certain acronyms stood for (SOLID, BASE and CAP); so, a bit architecture-y. I suggest, however, that the question about SOLID is actually a theoretical computer science issue rather than architecture - at least, architecture as I understand it. It's definitely useful to know and understand SOLID, but unless I'm interviewing for a computer science research position, I bet that you're interested in how I put that knowledge into practice in designing the best architecture for the application at hand.

Question six was back to architecture of sorts, but when you unpack the "Twelve Factor App Methodology" it's implementation (best practices) rather than architecture, and that makes the whole topic one of software engineering rather than architecture.

Yes, there's a difference.

Yes, it matters. (Also, yes, I'll ramble on about this in other posts - later).

Question seven was actual architecture:

Q7: What are Heuristic Exceptions?

This is a very good question, because it asks you to think about how to handle failure in the absence of a controller which tells your sub-process what to do. This is an area of clustered operation implementations which gets a lot of attention. In the clusterware environments that I've worked on, these clusters ran telco switches, billing systems, bank credit card transaction processors and even emergency service dispatch systems. You must get the response and system architecture correct because otherwise people could die.


The final two questions are also pretty good for architecture topics:

Q8: What is shared-nothing architecture? How does it scale? Q9: What does Eventually Consistent mean?

I first came across the shared-nothing architecture while reading a Sun Cluster docbook relating to the IBM Informix agent. At that time (circa 2001) the architecture appeared to be rare when used in the context of Sun Cluster or Veritas cluster. Now, however, it's pretty much the basis for any microservice you might want to spin up with Kubernetes or Docker.

Over the course of 2018 I interviewed 36 candidates for positions in the team I was working with inside Oracle. I asked questions relating to software engineering practice, to personal preferences (vi, emacs or VS code? Do you login as root or as your own user? were just two), knowledge of the standard C library, and just two that related in any way to architecture. For the record, those questions were

Is it better for your code to be correct or to be fast?

followup: can you think of a use-case for the other answer?


When you're designing a utility or application which requires the user provide a password, is it acceptable to provide the password as a command-line argument? What risks are there in doing so?

My gripe with this post on dev.to is that it's not just about software architecture, it's also about computer science and software engineering (not a bad thing at all) but most importantly, of the questions presented, the proposed answers for four of them depend more on whether you can regurgitate definitions from a textbook, rather than explain how the theory is usedin practice. If you're going for a position as a computer science academic then, sure, regurgitate the textbook definition. But otherwise, I want to know how you can put SOLID into practice.