How do you ensure 99.9% up-time?
Do you have a service that needs to be always up and running no matter what? How do you ensure it will? What provider do you use? How much do you pay?
I have an idea that I haven't validated yet. Before that I want to make sure technically it's a manageable project and I'm a bit worried if I have to have a cluster of at least 2 computers - in case one of them has an issue, the other one would be there - it would cost more than I can handle as a solopreneur without a stable business. I can imagine if there are multiple co-founders and/or investors it wouldn't be an issue, but I'm not planning to go to that path.
Can I do it cost-effectively or should I drop the idea and find something that is not so sensitive to the up-time? I mean without being a DevOps Ninja. I'm using Linux and familiar with some basic DevOps work, but I'm more into building the app (especially backend) than putting together the infrastructure behind it.
It would be a widget by the way that is embedded in my client's website and they could lose potential customers if the server is down and my widget is not working.
Use a Function as a Service, for AWS its a lambda function. It will scale up as needed. If you foresee a spike of people using your service then use provisioned concurrency
I go over availability in one of my blog posts https://www.tylerfarkas.ca/microservice/1/#high-availability-expectations
Infra wise use a managed service like Google Cloud Run in a couple of regions.
In terms of not pushing a broken update, try to isolate the part that really needs to be up from other parts (like user registration, profile update etc..)
Use a managed multi-region uptime monitor of the critical part and be able to rollback confidently.
Your idea doesn't sound all that critical, you should be fine.