I'd just use a service like Disqus or Google+ comments if you're a smaller website. It's easier with spam control and server use.
You can try creating your own service (serverless, API, or otherwise). Smashing Magazine runs on a JAMstack (Javascript app for the client on a CDN, APIs for everything else) and they're able to use a custom system for comments. People comment, it gets stored in a DB somewhere, and their static site gets rebuilt. Obviously if you're not static, you can just grab dynamically from the API.