next.js/examples/with-webpack-bundle-analyzer/next.config.js

const { BundleAnalyzerPlugin } = require('webpack-bundle-analyzer')
const { ANALYZE } = process.env

module.exports = {
  webpack: function (config, { isServer }) {
    if (ANALYZE) {
      config.plugins.push(new BundleAnalyzerPlugin({
        analyzerMode: 'server',
        analyzerPort: isServer ? 8888 : 8889,
        openAnalyzer: true
      }))
    }

    return config
  }
}