ratelimit-ssr.js

// Simplified Sample Code for limiting nuxt ssr per user

const { RateLimiterMemory } = require("rate-limiter-flexible");
const { cpuFree } = require('os-utils');

// each user has 1SSR per minute
const ipRateLimiter = new RateLimiterMemory({
  points: 1, // 1 SSR
  duration: 60, // Per minute
});

let warmup = true;
setTimeout(() =>  warmup = false, 60 * 1000); // 1-minute cooldown

let freeCpu = 1;
cpuFree(function h(val) {
  freeCpu = val;
  cpuFree(h);
});

// middleware used on express, before nuxt.render is called
module.exports = async function (req, res, next) {
  // in the first minute of starting server, SSR is disabled
  if (warmup || freeCpu < 0.2) res.spa = true;

  if (!res.spa) {
    const ip = req.headers['cf-connecting-ip'] || req.header('x-forwarded-for') || req.connection.remoteAddress;
    ipRateLimiter.consume(ip, 1)
      .catch(() => res.spa = true)
      .finally(next);
    return;
  }

  next();
};