razzle-plugin-node-runtime-vars.js

/**
 * The passed list of environment variables will be removed from the nodejs
 * instance of webpack.DefinePlugin, so they can be resolved dynamically at
 * runtime.
 * @example
 * // Include this in the plugins array exported by razzle.config.js
 * const nodeRuntimeVarsPlugin = createRazzlePluginNodeRuntimeVars('PORT', 'HOST');
 * @param  {String} ...nodeRuntimeVars
 * @return {Function}
 */
const createRazzlePluginNodeRuntimeVars = (...nodeRuntimeVars) => (
  config,
  { target, dev },
  webpack,
) => {
  if (target !== 'node') {
    // Don't change dotenv build-time behavior for the client bundle
    return config;
  }
  const definePluginIndex = config.plugins.findIndex(
    plugin => plugin instanceof webpack.DefinePlugin && plugin.definitions,
  );
  if (typeof definePluginIndex !== 'undefined') {
    const nodeRunetimeVarsBlacklist = nodeRuntimeVars.map(
      name => `process.env.${name}`,
    );
    const filteredDefinitions = config.plugins[definePluginIndex].definitions.entries().reduce((result, entry)=>{
      if (!nodeRunetimeVarsBlacklist.includes(entry[0])) {
        result[entry[0]] = entry[1];
      }
    }, {});
    config.plugins[definePluginIndex] = new webpack.DefinePlugin(
      filteredDefinitions,
    );
  }
  return config;
};

razzle.config.js

'use strict';

const createRazzlePluginNodeRuntimeVars = require('razzle-plugin-node-runtime-vars.js');

module.exports = {
  plugins: [createRazzlePluginNodeRuntimeVars('PORT', 'HOST')],
};

In razzle canary

'use strict';

module.exports = {
  options: {
      forceRuntimeEnvVars: ['PORT', 'HOST'],
  }
};