If your business can afford irregular downtime, by all means, go for it. Otherwise, you'll need to take precautions, and that will invariably make the system more complex than that.
As your business needs grow, you can start layering complexity on top. The point is you don't start at 11 with a overly complex architecture.
In your example, if your server crashes, just make sure you have some sort of automatic restart. In practice that may mean a downtime of seconds for your 12 users. Is that more complexity? Sure - but not much. If you need to take your service down for maintenance, you notify your 12 users and schedule it for 2am ... etc.
Later you could create a secondary cluster and stick a load-balancer in-front. You could also add a secondary replicated PostgreSQL instance. So the monolith/postgres architecture can actually take you far as your business grows.
It is common for founding engineers to start with a preexisting way of working that they import from their previous more-scaled company, and that approach is refined and compounded over time
It does mean starting with more than is necessary at the start, but that doesn't mean it has to be particularly complex. It means you start with heaps of already-solved problems that you simply never have to deal with, allowing focus on the product goals and deep technical investments that need to be specific to the new company
And if certain servers do get very important you just run a backup server with VPS and switch over DNS (even if you keep a high ttl, most servers update within minutes nowadays) or if you want to be fancy throw a load balancer in front of it.
If you solve issues in a few minutes people are always thankful, and most dont notice. With complicated setups it tends to take much longer before figuring out what the issue is in the first place.
Also in 5 years of working on both microservicy systems and monoliths, not once has these things you describe been a problem for me. Everything I've hosted in Azure has been perfectly available pretty much all the time unless a developer messed up or Azure itself has downtime that would have taken down either kind of app anyway.
But sure let's make our app 100 times more complicated because maybe some time in the next 10 years the complexity might save us an hour of downtime. I'd say it's more likely the added complexity will cause more downtime than it saves.
I don't think I implied that microservices are the solution, really. You can have a replicated monolith, but that absolutely adds complexity of its own.
> But sure let's make our app 100 times more complicated because maybe some time in the next 10 years the complexity might save us an hour of downtime.
Adding replicas and load balancing doesn't have to be a hundred times more complex.
> I'd say it's more likely the added complexity will cause more downtime than it saves.
As I said before, this is an assessment you will need to make for your use case, and balance uptime requirements against your complexity budget; either answer is valid, as long as you feel confident with it. Only a Sith believes in absolutes.
