New release is coming soon! If you want to try out the latest features, simply run npm i -s moleculer@next. The docs for the latest version are available here.

Moleculer Runner

Moleculer Runner is a helper script that helps you run Moleculer projects. With it, you don’t need to create a ServiceBroker instance with options. Instead, you can create a moleculer.config.js file in the root of repo with broker options. Then simply call the moleculer-runner in NPM script, and it will automatically load the configuration file, create the broker and load the services. Alternatively, you can declare your configuration as environment variables.


Use the moleculer.config.js during development or store common options. In production, you can overwrite the values with the environment variables!


$ moleculer-runner [options] [service files or directories or glob masks]

Note: It runs in this format in NPM scripts only. To call it directly from your console, use the ./node_modules/.bin/moleculer-runner --repl or node ./node_modules/moleculer/bin/moleculer-runner.js --repl format.


Option Type Default Description
-r, --repl Boolean false If true, it switches to REPL mode after broker started.
-s, --silent Boolean false Disable the broker logger. It prints nothing to the console.
-H, --hot Boolean false Hot reload services when they change.
-c, --config <file> String null Load configuration file from a different path or a different filename.
-e, --env Boolean false Load environment variables from the ‘.env’ file from the current folder.
-E, --envfile <file> String null Load environment variables from the specified file.
-i, --instances Number null Launch [number] node instances or max for all cpu cores (with cluster module)

Example NPM scripts

"scripts": {
"dev": "moleculer-runner --repl --hot --config services",
"start": "moleculer-runner --instances=max services"

The dev script loads development configurations from the file, start all services from the services folder, enable hot-reloading and switches to REPL mode. Run it with the npm run dev command.

The start script is to load the default moleculer.config.js file if it exists, otherwise only loads options from environment variables. Starts 4 instances of broker, then they start all services from the services folder. Run it with npm start command.

Configuration loading logic

The runner does the following steps to load & merge configurations:

  1. Load the config file defined in MOLECULER_CONFIG environment variable. If it does not exist, it throws an error.
  2. It loads config file defined in CLI options. If it does not exist, it throws an error. Note that MOLECULER_CONFIG has priority over CLI meaning that if both are defined MOLECULER_CONFIG is the one that’s going to be used.
  3. If not defined, it loads the moleculer.config.js file from the current directory. If it does not exist, it loads the moleculer.config.json file.
  4. Once a config file has been loaded, it merges options with the default options of the ServiceBroker.
  5. The runner observes the options step by step and tries to overwrite them from environment variables. Once logLevel: "warn" is set in the config file, but the LOGLEVEL=debug environment variable is defined, the runner overwrites it, and it results: logLevel: "debug".

To overwrite broker’s deeply nested default options, which are not present in moleculer.config.js, via environment variables, use the MOL_ prefix and double underscore __ for nested properties in .env file. For example, to set the cacher prefix to MOL you should declare as MOL_CACHER__OPTIONS__PREFIX=MOL.

Configuration file

The structure of the configuration file is the same as that of the broker options. Every property has the same name.

Example config file

// moleculer.config.js
module.exports = {
nodeID: "node-test",
logger: true,
logLevel: "debug",

transporter: "nats://localhost:4222",
requestTimeout: 5 * 1000,

circuitBreaker: {
enabled: true

metrics: true

Asynchronous Configuration file

Moleculer Runner also supports asynchronous configuration files. In this case moleculer.config.js must export a Function that returns a Promise (or you can use async/await).

// moleculer.config.js
const fetch = require("node-fetch");

module.exports = async function() {
const res = await fetch("");
return await res.json();

This function runs with the MoleculerRunner instance as the this context. Useful if you need to access the flags passed to the runner. Check the MoleculerRunner source more details.

Environment variables

The runner transforms the property names to uppercase. If nested, the runner concatenates names with _.

Example environment variables


# Shorthand transporter

# Nested property


Services loading logic

The runner loads service files or folders defined in CLI arguments. If you define folder(s), the runner loads all services **/*.service.js from specified one(s) (including sub-folders too). Services & service folder can be loaded with SERVICES and SERVICEDIR environment variables.

Loading steps:

  1. If SERVICEDIR env found, but no SERVICES env, it loads all services from the SERVICEDIR directory.
  2. If SERVICEDIR & SERVICES env found, it loads the specified services from the SERVICEDIR directory.
  3. If no SERVICEDIR, but SERVICES env found, it loads the specified services from the current directory.
  4. Check the CLI arguments. If filename found, it loads them. If directory found, it loads them. If glob pattern found, it applies and load the found files.

Please note: shorthand names can also be used in SERVICES env var.



It loads the math.service.js, post.service.js and user.service.js files from the services folder.


It loads all *.service.js files from the my-services folder (including sub-folders too).

Glob patterns

If you want to be more specific, use glob patterns. It is useful when loading all services except certain ones.

$ moleculer-runner services !services/others/**/*.service.js services/others/mandatory/main.service.js


  • services - legacy mode. Load all services from the services folder with **/*.service.js file mask.
  • !services/others/**/*.service.js - skip all services in the services/others folder and sub-folders.
  • services/others/mandatory/main.service.js - load the exact service.

The glob patterns work in the SERVICES environment variables, as well.

Built-in clustering

Moleculer Runner has a built-in clustering function to start multiple instances from your broker.

Example to start all services from the services folder in 4 instances.

$ moleculer-runner --instances 4 services
Clustered Node ID

The nodeID will be suffixed with the worker ID. E.g. if you define my-node nodeID in options, and starts 4 instances, the instance nodeIDs will be my-node-1, my-node-2, my-node-3, my-node-4.

.env files

Moleculer runner can load .env file at starting. There are two new cli options to load env file:

  • -e, --env - Load environment variables from the ‘.env’ file from the current folder.
  • -E, --envfile <filename> - Load environment variables from the specified file.


# Load the default .env file from current directory
$ moleculer-runner --env

# Load the specified .my-env file
$ moleculer-runner --envfile .my-env

To use this feature, install the dotenv module with npm install dotenv --save command.