robustly-start-vm/index.js

robustly start a vm on Google Compute Engine; if a zone is full retry using your supplied template functions

// robustly-start-vm Copyright 2018 Paul Brewer, Economic and Financial Technology Consulting LLC
// This software is open source software available under the terms of the MIT License
// https://opensource.org/licenses/MIT
// This software is NOT a product of Google, Inc.

// jshint node:true, esversion:6

/**
 * returns the robustlyStartVM function.  new VMs must have names starting with the configured safety string.
 * @param {Object} gce result from calling `const gce = require('@google-cloud/compute')()
 * @param {string} safety (required) sets the safety string.  Creating a VM with a name that does not start with the safety string is forbidden.
 * @param {number} timeout (optional, default 30000) delay in ms to retry creating a vm that failed to start
 * @return {Function} robustlyStartVM
 */

const promiseRetry = require('promise-retry');
const Boom = require('boom');

function toRegion(z) {
  // remove the dash and the last letter from the zone to get the region
  return z.replace(/-.$/, '');
}

module.exports = function (gce, safety, timeout) {
  if (typeof(safety) !== "string") throw new Error("safety must be a string");
  if (safety.length === 0) throw new Error("safety string must not be length 0");
  return function({ zones, vmname, diskFunc, vmFunc }) {
    if (!safety || !(vmname.startsWith(safety))) throw new Error("bad vmname ${vmname}");
    if (!Array.isArray(zones)) throw new Error("bad or missing array zones");
    if (typeof(vmname) !== "string") throw new Error("bad or missing string vmname");
    if (typeof(diskFunc) !== "function") throw new Error("bad or missing function diskFunc");
    if (typeof(vmFunc) !== "function") throw new Error("bad or missing function vmFunc");

    function locationForAttempt(n) {
      return { 'zone': zones[n - 1], 'region': toRegion(zones[n - 1]) };
    }

    function diskForAttempt(n) {
      return diskFunc(locationForAttempt(n));
    }

    function vmForAttempt(n) {
      return vmFunc(locationForAttempt(n));
    }

    function deleteOldDisk(n) {
      const gzone = gce.zone(locationForAttempt(n - 1).zone);
      return (
        gzone
        .disk(vmname)
        .delete()
        .catch((ee) => console.log(`Cleanup error on disk deletion ${vmname}: ${ee}. `))
      );
    }

    function attemptStartVM(retry, attemptNumber) {
      if (attemptNumber === 0) throw new Error("promise-rety attemptNumber should never be zero, but it is zero");
      if ((attemptNumber > 3) || (attemptNumber > zones.length))
        throw new Error("VM creation failed. Too busy. Please try again later.");
      const gzone = gce.zone(locationForAttempt(attemptNumber).zone);
      const prep = (attemptNumber <= 1) ? Promise.resolve(0) : deleteOldDisk(attemptNumber);
      return (prep
        .then(() => (gzone.createDisk(vmname, diskForAttempt(attemptNumber))))
        .then((data) => {
          // const disk = data[0];
          const operation = data[1];
          // const apiResponse = data[2];
          return operation.promise();
        })
        .then(() => (gzone
            .createVM(vmname, vmForAttempt(attemptNumber))
            .then((data) => {
              // const vm = data[0];
              const operation = data[1];
              // const apiResponse = data[2];
              return operation.promise();
            })
          )
        )
        .then(()=>locationForAttempt(attemptNumber))
        .catch((e) => {
          const lowerCaseErrorMessage = e.toString().toLowerCase();
          if (lowerCaseErrorMessage.includes("already exists")) {
            throw Boom.conflict(e.toString());
          }
          const retryOnTheseErrors = [
            "try a different zone",
            "unknown zone"
          ];
          if (retryOnTheseErrors.some((excuse)=>(lowerCaseErrorMessage.includes(excuse)))){
            retry(e);
          } else {
            throw e;
          }
        })
      );
    }
    return promiseRetry(attemptStartVM, { retries: zones.length - 1, minTimeout: (timeout || 30000), factor: 1.5 });
  };
};