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Why do you assume they have more fault tolerance scenarios simply because they have more deployable units? In every service architecture I've worked with in the last few years, you could theoretically run every single "service" within the same physical process -- provided they all shared the same runtime/lang the way a monolith does. I tend to start service architectures using Ruby exclusively with the Eventide toolkit, so this is actually a viable approach for most teams I've worked with. But it's never ultimately made sense. Weighing the pros/cons, a consolidated deployment topology wouldn't add any benefit, and it would actually make it far more difficult for the operations folks, practically speaking. I've helped put services into production that 1. carry out crucial, "core" business logic reliably and efficiently, 2. can be scaled horizontally without changing the code, 3. never raise exceptions or cause outages, and 4. don't need to be touched for years because new features are more naturally composed around them anyways (i.e. open/closed principle). Practically speaking, it's quite a bit easier for human programmers to reach this degree of precision with a smaller program than with a much larger one. And if you add up a lot of these high quality programs, you get a high quality system. Building a high quality system out of a single program is much, much harder for humans in practice. I'll use crude terms here for a second: every good service put into production brings a net benefit to the organization relative to the same code having been entangled with an existing pile of code. That may sound like a "No True Scotsman" fallacy, but the definition of "good" in this context is precisely the net benefit being added. If you build and deploy services that have a high degree of quality, you get a corresponding benefit. If you build and deploy programs that _don't_ stand on their own, _don't_ leverage durable messaging, and take other programs down with them when they crash, then you get a rather large mess on your hands. In fact, you never had a service architecture at all; we call this failure mode a "distributed monolith." I'll acknowledge that most attempts at microservice architectures in the wild don't seem to succeed. Anecdotally, they are particularly prone to failure when their architects don't understand the underlying principles of distributed systems all that well; they neglect important considerations like messaging idempotence, the deleterious effect of synchronous request/response messaging, and the need for deliberate, thoughtful design. In other words, they build systems out of N number of microservices, and get N^2 fault tolerance scenarios, which you adeptly called out for being foolish. They're arguably worse off than if they went with a monolith, but neither would be an architecture I'd personally want to work with. |
Though the transition is still in progress, I can say that the path forward is clear and hopeful. This company had previously explored other "SOA" paths (distributed monolith) and it was clear that those were very problematic. Luckily, we were able to steer them to an actual evented architecture.
As I said, it's still early days for this particular project, but if you're feeling your monolith is getting harder and harder to develop on, you should start looking into evented architectures. Eventide (ruby)/messagedb (postgresql) are awesome technologies and would be the first I'd consider. Eventide also has a nice slack community filled with people that are learning and improving their software design skill both in the large (architecture) and the small (individual classes/etc). It's small, but they're good people.