Getting Serverless variables from terraform state

config.js

const exec = require('child_process').exec;

function terraformOutput(name, tfModule) {
  let mod = tfModule != undefined ? `-module ${tfModule}` : '';
  let cmd = `terraform output -json ${mod}`;

  let outputs = new Promise((resolve, reject) => {
    exec(cmd, {'cwd': 'infrastructure'},
      (error, stdout, stderr) => {
        if (error) reject(error);
        else resolve(stdout);
      }
    )
  });
  return outputs
    .then(JSON.parse)
    .then(d => d[name].value);
}

module.exports = () => {
  return {
    web_bucket: terraformOutput('web_bucket', 'hosting'),
    publisher_role: terraformOutput('publisher_role')
  }
}

serverless.yml

custom: ${file(./config.js)}
# then refer to the variables with ${self:custom.web_bucket}