I've done some basic benchmarks and it has scaled pretty well. Mostly thanks to the excellent performance and scalability that comes from choosing Go and Postgres. IMO backend servers are where Go excels.

I'm planning on adding Redis support soon enough so that sudden spikes would have little impact on the database server (which is nearly always the bottleneck, unless you're compute-intensive, which isn't the case with Commento). So that if you suddenly get a few hundred thousand visitors, most API responses are cached and only a fraction will actually require disk access. Like reddit does, where it'll temporarily say there N comments, but when you open the page, there wouldn't be that many. A few seconds of inconsistency is a fine compromise in the comments world. Of course, Redis isn't going to magically make everything faster, so I'll have to be careful with where I introduce it. Optimise for the common case and all that.

I'm still in uni, and I've never actually worked on large-throughput, high-scalability stuff before, so all this has been a great learning experience for me. If you have any suggestions or war stories that might be relevant, I'm all ears!