How I run/scale the infrastructure to process 10,000s payments every month

Short answer: I don't. It's fully hosted for me. Don't waste time rolling your own infrastructure. You'll pay more in the long run in time wasted, downtime, and worse developer experience.

Long answer:

From day 1 I've never run my own servers or databases at SuperPay (https://superpayit.com). Not because I don't know how-to, it's that I know I could better spend time building features my users care about. Not worrying about running highly-available infrastructure, autoscaling, load balancing, and all the other fun things that come with rolling your own setup.

So how is SuperPay hosted?

We use Heroku (https://heroku.com). Heroku is an example of a PaaS (Platform as a Service). We pay a monthly fee for the servers and databases we use and Heroku takes care of everything hosting related. Basically everything you need to host a web app or API securely and with high uptime.

Many people say "Heroku is really expensive, you can get 4x the power with DigitalOcean (https://www.digitalocean.com/)". And don't get me wrong that's true, but that's forgetting that DigitalOcean gives you the raw virtual servers, that's it. No OS patching, auto-updates, automatic failover, etc.

When running a SaaS company, especially when bootstrapping, time is your most valuable resource. And what you decide to focus that time on is a critical part of whether it'll be a success.

What PaaS should I choose?
I choose Heroku for SuperPay for their uptime, reliability, and a huge amount of experience in running this type of platform. They have been around for more than a decade - you definitely learn a lot of important lessons over that time. Plus they're owned by Salesforce so there is a pretty good guarantee that they'll still be around and thriving in 10 years.

But there are loads out there, two I particularly like are Pythonanywhere (https://www.pythonanywhere.com/) and Render (https://render.com/)

Newer ones I've not used yet but have heard amazing things about are Zeet (https://zeet.co/) and Deta (https://www.deta.sh/).

I understand that not every SaaS can run on a PaaS, for example, if you have some crazy infra requirements for other non-standard workloads. But if you're currently debating to choose between self-hosting on something like AWS or choosing a PaaS like Heroku, choose a PaaS. You'll thank yourself later.

If you found this interesting here's my Twitter: https://twitter.com/che_sampat