code: function addInstance(machineName, versionKey) {
  
          return co(function*() {
              debug("Adding a new instance to the " + versionKey + " of the '" + machineName + "' machine");
              let manifest = getManifest();
  
              let machine = manifest.machines[machineName];
              if (!machine) {
                  throw new Error("Machine does not exists");
              }
  
              let version = machine.versions[versionKey];
              if (!version) {
                  throw new Error("Version does not exists");
              }
  
              let versionInfo = getVersionInfo(machineName,  versionKey);
              if(!versionInfo.isSealed) {
                  throw new Error("The version is not sealed yet");
              }
  
              let newInstanceKey = "instance" + (Object.keys(version.instances).length + 1);
              let instanceDirPath = version.route + "/instances/" + newInstanceKey;
              let instanceSnapshotsDirPath = instanceDirPath + "/snapshots";
              version.instances[newInstanceKey] = {
                  "route": instanceDirPath,
                  "snapshots": {}
              };
  
              let infoFile = instanceDirPath + "/info.json";
  
              debug("Creating the directories");
              fs.mkdirSync(repositoryPath + "/" + instanceDirPath);
              fs.mkdirSync(repositoryPath + "/" + instanceSnapshotsDirPath);
  
              debug("Creating the instance info.json file");
              let info = {
                  "hasStarted": false,
                  "hasEnded": false
              };
              jsonfile.writeFileSync(repositoryPath + "/" + infoFile, info);
  
              debug("Setting the manifest");
              setManifest(manifest);
              yield _commit(null, ["manifest.json", infoFile],
                  "Created the "+newInstanceKey+" for the "+versionKey+" of the '" + machineName + "' machine");
  
              return newInstanceKey;
          });
      }
docs: Add a new instance to a version of a machine
  @method addInstance
  @param {String} machineName The name of the machine
  @param {String} versionKey The key of the version
  @returns {Promise} The instance key