I am having trouble understand what Pulumi does, since I rarely work in web architecture. Could someone explain it?
It's super useful and compelling at scale, but there are some potential downsides. For one, it's a real program and IMHO you should treat it as such with the same rigor of documentation, testing, etc. as the production code you're deploying. This might actually make your processes a bit slower or more risky. Because if you don't do that then you just risk building unmaintainable, untrustworthy deployment code that nobody wants to use.
The second downside is you're taking a big bet on Pulumi to stick around. At this point, it's probably a safe bet. But the more you use their SDK and system the more tightly coupled your production deployment is to the continued existence of Pulumi. If they go bust and can't maintain the SDK you might have a production system that can't be deployed anymore.
Sounds like a neat and useful project for complex setups.
There's really no definitive 'winner' or best option yet. Each has strengths and weaknesses relative to others. It might just come down to how a team prefers to manage and work with infrastructure.
Still, Terraform has my needs at this stage and looks a lot more mature. But if I was a small web host or something this could be a really interesting integration.
In that case, you can save your state in an S3 bucket, just like you save your Terraform state somewhere.
For me the biggest benefit is the fact that I can write my infra with Types in TypeScript.
See native provider.