[kbn/es] add --download flag to snapshot command to warm the cache (#25830)

In order to pre-fetch Elasticsearch snapshots and avoid timeouts during download in images, this adds a `--download` option to the `es snapshot` command.

packages/kbn-es/src/cli_commands/snapshot.js

@@ -35,6 +35,7 @@ exports.help = (defaults = {}) => {
       --install-path  Installation path, defaults to 'source' within base-path
       --password      Sets password for elastic user [default: ${password}]
       -E              Additional key=value settings to pass to Elasticsearch
+      --download-only Download the snapshot but don't actually start it
 
     Example:
 
@@ -51,10 +52,16 @@ exports.run = async (defaults = {}) => {
       esArgs: 'E',
     },
 
+    boolean: ['download-only'],
+
     default: defaults,
   });
 
   const cluster = new Cluster();
-  const { installPath } = await cluster.installSnapshot(options);
-  await cluster.run(installPath, { esArgs: options.esArgs });
+  if (options['download-only']) {
+    await cluster.downloadSnapshot(options);
+  } else {
+    const { installPath } = await cluster.installSnapshot(options);
+    await cluster.run(installPath, { esArgs: options.esArgs });
+  }
 };

packages/kbn-es/src/cluster.js

@@ -19,7 +19,7 @@
 
 const execa = require('execa');
 const chalk = require('chalk');
-const { installSnapshot, installSource, installArchive } = require('./install');
+const { downloadSnapshot, installSnapshot, installSource, installArchive } = require('./install');
 const { ES_BIN } = require('./paths');
 const { log: defaultLog, parseEsLog, extractConfigFiles } = require('./utils');
 const { createCliError } = require('./errors');
@@ -50,6 +50,28 @@ exports.Cluster = class Cluster {
     return { installPath };
   }
 
+  /**
+   * Download ES from a snapshot
+   *
+   * @param {Object} options
+   * @property {Array} options.installPath
+   * @property {Array} options.sourcePath
+   * @returns {Promise<{installPath}>}
+   */
+  async downloadSnapshot(options = {}) {
+    this._log.info(chalk.bold('Downloading snapshot'));
+    this._log.indent(4);
+
+    const { installPath } = await downloadSnapshot({
+      log: this._log,
+      ...options,
+    });
+
+    this._log.indent(-4);
+
+    return { installPath };
+  }
+
   /**
    * Download and installs ES from a snapshot
    *

packages/kbn-es/src/install/index.js

@@ -19,4 +19,5 @@
 
 exports.installArchive = require('./archive').installArchive;
 exports.installSnapshot = require('./snapshot').installSnapshot;
+exports.downloadSnapshot = require('./snapshot').downloadSnapshot;
 exports.installSource = require('./source').installSource;

packages/kbn-es/src/install/snapshot.js

@@ -27,6 +27,39 @@ const { BASE_PATH } = require('../paths');
 const { installArchive } = require('./archive');
 const { log: defaultLog, cache } = require('../utils');
 
+/**
+ * Download an ES snapshot
+ *
+ * @param {Object} options
+ * @property {('oss'|'basic'|'trial')} options.license
+ * @property {String} options.version
+ * @property {String} options.basePath
+ * @property {String} options.installPath
+ * @property {ToolingLog} options.log
+ */
+exports.downloadSnapshot = async function installSnapshot({
+  license = 'basic',
+  version,
+  basePath = BASE_PATH,
+  installPath = path.resolve(basePath, version),
+  log = defaultLog,
+}) {
+  // TODO: remove -alpha1 once elastic/elasticsearch#35172 has been merged
+  const fileName = getFilename(license, version + '-alpha1');
+  const url = `https://snapshots.elastic.co/downloads/elasticsearch/${fileName}`;
+  const dest = path.resolve(basePath, 'cache', fileName);
+
+  log.info('version: %s', chalk.bold(version));
+  log.info('install path: %s', chalk.bold(installPath));
+  log.info('license: %s', chalk.bold(license));
+
+  await downloadFile(url, dest, log);
+
+  return {
+    downloadPath: dest,
+  };
+};
+
 /**
  * Installs ES from snapshot
  *
@@ -46,17 +79,15 @@ exports.installSnapshot = async function installSnapshot({
   installPath = path.resolve(basePath, version),
   log = defaultLog,
 }) {
-  // TODO: remove -alpha1 once elastic/elasticsearch#35172 has been merged
-  const fileName = getFilename(license, version + '-alpha1');
-  const url = `https://snapshots.elastic.co/downloads/elasticsearch/${fileName}`;
-  const dest = path.resolve(basePath, 'cache', fileName);
+  const { downloadPath } = await exports.downloadSnapshot({
+    license,
+    version,
+    basePath,
+    installPath,
+    log,
+  });
 
-  log.info('version: %s', chalk.bold(version));
-  log.info('install path: %s', chalk.bold(installPath));
-  log.info('license: %s', chalk.bold(license));
-
-  await downloadFile(url, dest, log);
-  return await installArchive(dest, {
+  return await installArchive(downloadPath, {
     license,
     password,
     basePath,