Service

The Service represents a microservice in the Moleculer. You can define actions and subscribe to events. To create a service you need to define a schema. The service schema is similar to a component of VueJS.

Schema

The schema has some main parts: name, version, settings, actions, methods, events.

Simple service schema to define two actions

{
name: "math",
actions: {
add(ctx) {
return Number(ctx.params.a) + Number(ctx.params.b);
},
sub(ctx) {
return Number(ctx.params.a) - Number(ctx.params.b);
}
}
}

Base properties

The Service has some base properties in the schema.

{
name: "posts",
version: 1
}

The name is a mandatory property so it must be defined. It’s the first part of action name when you call it with broker.call.

To disable service name prefixing set $noServiceNamePrefix: true in Service settings.

The version is an optional property. Use it to run multiple version from the same service. It is a prefix in the actionName. It can be a Number or a String.

{
name: "posts",
version: 2,
actions: {
find() {...}
}
}

You can call this find action on version 2 service:

broker.call("v2.posts.find");

REST call

If you are using our Moleculer Web module, you can request it as GET /v2/posts/find.

To disable version prefixing set $noVersionPrefix: true in Service settings.

Settings

The settings property is a store, where you can store every settings/options to your service. You can reach it via this.settings inside the service.

{
name: "mailer",
settings: {
transport: "mailgun"
},
action: {
send(ctx) {
if (this.settings.transport == "mailgun") {
...
}
}
}
}

The settings is also obtainable on remote nodes. It is transferred during service discovering.

Internal settings

There are some internal settings which are used by core modules. These setting names start with $ (dollar sign).

Name Type Default Description
$noVersionPrefix Boolean false Disable version prefixing in action names.
$noServiceNamePrefix Boolean false Disable service name prefixing in action names.
$dependencyTimeout Number 0 Timeout for dependency waiting.

Mixins

Mixins are a flexible way to distribute reusable functionalities for Moleculer services. The Service constructor merges these mixins with the current schema. It is to extend an other service in your service. When a service uses mixins, all properties in the mixin will be “mixed” into the current service.

Example how to extend moleculer-web service

const ApiGwService = require("moleculer-web");
module.exports = {
name: "api",
mixins: [ApiGwService]
settings: {
// Change port setting
port: 8080
},
actions: {
myAction() {
// Add a new action to apiGwService service
}
}
}

The above example creates an api service which inherits all from ApiGwService but overwrite the port setting and extend it with a new myAction action.

Merge algorithm

The merge algorithm depends on the property type.

Property Algorithm
name, version Merge & overwrite.
settings Extend with defaultsDeep.
actions Extend with defaultsDeep. You can disable an action from mixin if you set to false in your service.
methods Merge & overwrite.
events Concatenate listeners.
created, started, stopped Concatenate listeners.
mixins Concatenate listeners.
any other Merge & overwrite.
Merge algorithm examples

Merge & overwrite: if serviceA has a: 5, b: 8 and serviceB has c: 10, b: 15, the mixed service will have a: 5, b: 15 and c: 10.
Concatenate: if serviceA & serviceB subscribe to users.created event, both event handler will be called when the users.created event emitted.

Actions

The actions are the callable/public methods of the service. They are callable with broker.call.
The action could be a function (shorthand for handler) or an object with some properties above all with the handler.
The actions should be placed under the actions key in the schema.

module.exports = {
name: "math",
actions: {
// Shorthand definition, only the handler function
add(ctx) {
return Number(ctx.params.a) + Number(ctx.params.b);
},
// Normal definition with other properties. In this case
// the `handler` function is required!
mult: {
cache: false,
params: {
a: "number",
b: "number"
},
handler(ctx) {
// The action properties are accessible as `ctx.action.*`
if (!ctx.action.cache)
return Number(ctx.params.a) * Number(ctx.params.b);
}
}
}
};

You can call the above actions as

const res = await broker.call("math.add", { a: 5, b: 7 });
const res = await broker.call("math.mult", { a: 10, b: 31 });

Inside the action you can call other nested actions in other services with ctx.call method. It is an alias to broker.call, just set itself as parent context (due tracing).

module.exports = {
name: "posts",
actions: {
async get(ctx) {
// Find a post by ID
let post = posts[ctx.params.id];
// Populate the post.author field through "users" service
// Call the "users.get" action with author ID
const user = await ctx.call("users.get", { id: post.author });
if (user) {
// Replace the author ID with the received user object
post.author = user;
}
return post;
}
}
};

In handlers the this is always pointed to the Service instance.

Events

You can subscribe to events under the events key.

module.exports = {
name: "report",
events: {
// Subscribe to "user.created" event
"user.created"(payload) {
this.logger.info("User created:", payload);
// Do something
},
// Subscribe to all "user.*" event
"user.*"(payload, sender, eventName) {
// Do something with payload. The `eventName` contains
// the original event name. E.g. `user.modified`.
// The `sender` is the nodeID of sender.
}
// Subscribe to a local event
"$node.connected"({ node }) {
this.logger.info(`Node '${node.id}' is connected!`);
}
}
};

In handlers the this is always pointed to the Service instance.

Grouping

The broker groups the event listeners by group name. By default, The group name is the service name. But you can change it in the event definition.

module.exports = {
name: "payment",
events: {
"order.created": {
// Register handler to the "other" group instead of "payment" group.
group: "other",
handler(payload) {
// ...
}
}
}
}

Methods

You can also create private methods in the Service. They are under the methods key. These functions are private, can’t be called with broker.call. But you can call it inside service (from action handlers, event handlers and lifecycle event handlers).

Usage

module.exports = {
name: "mailer",
actions: {
send(ctx) {
// Call the `sendMail` method
return this.sendMail(ctx.params.recipients, ctx.params.subject, ctx.params.body);
}
},
methods: {
// Send an email to recipients
sendMail(recipients, subject, body) {
return new Promise((resolve, reject) => {
...
});
}
}
};

The name of the method can’t be name, version, settings, schema, broker, actions, logger, because these words are reserved in the schema.

In methods the this is always pointed to the Service instance.

Lifecycle events

There are some lifecycle service events, that will be triggered by broker.

module.exports = {
name: "www",
actions: {...},
events: {...},
methods: {...},
created() {
// Fired when the service instance created. (broker.loadService or broker.createService)
},
async started() {
// Fired when `broker.start()` called.
}
async stopped() {
// Fired when `broker.stop()` called.
}
};

Dependencies

If your service depends on other services, use the dependencies property in the schema. The service can wait for other services before starting. It uses the broker waitForServices method.

module.exports = {
name: "posts",
settings: {
$dependencyTimeout: 30000 // Default: 0 - no timeout
},
dependencies: [
"likes", // shorthand w/o version
{ name: "users", version: 2 }, // with numeric version
{ name: "comments", version: "staging" } // with string version
],
async started() {
this.logger.info("It will be called after all dependent services are available.");
const users = await this.broker.call("users.list");
}
....
}

The started service handler is called once the likes, users and comments services are available (either the local or remote nodes).

Metadata

The Service schema has a metadata property. You can store here any meta information about service. You can access it as this.metadata inside service functions.
Moleculer modules don’t use it. You can store it whatever you want.

module.exports = {
name: "posts",
settings: {},
metadata: {
scalable: true,
priority: 5
},
actions: { ... }
};

The metadata is transferred among other nodes, you can access it via $node.services on other nodes.

Properties of this

In service functions, this is always pointed to the Service instance. It has some properties & methods which you can use in your service functions.

Name Type Description
this.name String Name of service (from schema)
this.version Number or String Version of service (from schema)
this.settings Object Settings of service (from schema)
this.metadata Object Metadata of service (from schema)
this.schema Object Schema definition of service
this.broker ServiceBroker Instance of broker
this.Promise Promise Class of Promise (Bluebird)
this.logger Logger Logger instance
this.actions Object Actions of service. Service can call own actions directly but it is not recommended. Use the ctx.call instead!
this.waitForServices Function Link to ‘broker.waitForServices’ method

Create a service

There are several ways to create and load a service.

broker.createService()

Call the broker.createService method with the schema of service as the first argument. It’s simple & fast. Use it when you are developing or prototyping.

broker.createService({
name: "math",
actions: {
add(ctx) {
return Number(ctx.params.a) + Number(ctx.params.b);
}
}
});

Load service from file

The recommended way is to place your service code into a single file and load it with the broker.

math.service.js
// Export the schema of service
module.exports = {
name: "math",
actions: {
add(ctx) {
return Number(ctx.params.a) + Number(ctx.params.b);
},
sub(ctx) {
return Number(ctx.params.a) - Number(ctx.params.b);
}
}
}

Load it with broker:

index.js
// Create broker
let broker = new ServiceBroker();
// Load service
broker.loadService("./math.service");
// Start broker
broker.start();

In the service file you can also create the Service instance. In this case, you have to export a function which returns the instance of Service.

const { Service } = require("moleculer");
// Export a function, the `loadService` will call it with the ServiceBroker instance.
module.exports = function(broker) {
return new Service(broker, {
name: "math",
actions: {
add(ctx) {
return Number(ctx.params.a) + Number(ctx.params.b);
},
sub(ctx) {
return Number(ctx.params.a) - Number(ctx.params.b);
}
}
});
}

Or create a function which returns with the schema of service

// Export a function, the `loadService` will call with the ServiceBroker instance.
module.exports = function() {
let users = [....];
return {
name: "math",
actions: {
create(ctx) {
users.push(ctx.params);
}
}
};
}

Load multiple services from a folder

If you have many services (and you will have) we suggest to put them to a services folder and load all of them with the broker.loadServices method.

Syntax

broker.loadServices(folder = "./services", fileMask = "**/*.service.js");

Example

// Load every *.service.js file from the "./services" folder (including subfolders)
broker.loadServices();
// Load every *.service.js file from the current folder (including subfolders)
broker.loadServices("./");
// Load every user*.service.js file from the "./svc" folder
broker.loadServices("./svc", "user*.service.js");

Load with Moleculer Runner (recommended)

We recommend to use the Moleculer Runner to start a ServiceBroker and load services. Read more about Moleculer Runner. It is the easiest way to start a node.

Hot reloading services

When you are developing your microservices project would be useful a hot reload function which reloads your services when you modify it. Moleculer has a built-in hot-reloading function. You can enable it in broker options or in Moleculer Runner.
Demo video how it works.

Usage

let broker = new ServiceBroker({
logger: console,
hotReload: true
});
broker.loadService("./services/test.service.js");

Usage with Moleculer Runner

Turn it on with --hot or -H flags.

$ moleculer-runner --hot ./services/test.service.js

Hot reloading function is working only with Moleculer Runner or if you load your services with broker.loadService or broker.loadServices. It doesn’t work with broker.createService.

Hot reloading is only watch the service.js file. If you are using additional JS files in your services and they are changed, broker won’t detect it. In this case it is better to use nodemon to restart all services and broker.

Local variables

If you would like to use local properties/variables in your service, declare them in the created event handler.

Example for local variables

const http = require("http");
module.exports = {
name: "www",
settings: {
port: 3000
},
created() {
// Create HTTP server
this.server = http.createServer(this.httpHandler);
},
started() {
// Listening...
this.server.listen(this.settings.port);
},
stopped() {
// Stop server
this.server.close();
},
methods() {
// HTTP handler
httpHandler(req, res) {
res.end("Hello Moleculer!");
}
}
}

Naming restriction

It is important to be aware that you can’t use variable name which is reserved for service or coincides with your method names! E.g. this.name, this.version, this.settings, this.schema…etc.

ES6 classes

If you like better ES6 classes than Moleculer service schema, you can write your services in ES6 classes. There are two ways to do it.

Native ES6 classes with schema parsing

Define actions and events handlers as class methods. Call the parseServiceSchema method in constructor with schema definition where the handlers pointed to these class methods.

const Service = require("moleculer").Service;
class GreeterService extends Service {
constructor(broker) {
super(broker);
this.parseServiceSchema({
name: "greeter",
version: "v2",
meta: {
scalable: true
},
dependencies: [
"auth",
"users"
],
settings: {
upperCase: true
},
actions: {
hello: this.hello,
welcome: {
cache: {
keys: ["name"]
},
params: {
name: "string"
},
handler: this.welcome
}
},
events: {
"user.created": this.userCreated
},
created: this.serviceCreated,
started: this.serviceStarted,
stopped: this.serviceStopped,
});
}
// Action handler
hello() {
return "Hello Moleculer";
}
// Action handler
welcome(ctx) {
return this.sayWelcome(ctx.params.name);
}
// Private method
sayWelcome(name) {
this.logger.info("Say hello to", name);
return `Welcome, ${this.settings.upperCase ? name.toUpperCase() : name}`;
}
// Event handler
userCreated(user) {
this.broker.call("mail.send", { user });
}
serviceCreated() {
this.logger.info("ES6 Service created.");
}
serviceStarted() {
this.logger.info("ES6 Service started.");
}
serviceStopped() {
this.logger.info("ES6 Service stopped.");
}
}
module.exports = GreeterService;

Use decorators

Thanks for @ColonelBundy, you can use ES7/TS decorators as well: moleculer-decorators

Need a compiler

Please note, you need to use Typescript or Babel to compile decorators.

Example service

const moleculer = require('moleculer');
const { Service, Action, Event, Method } = require('moleculer-decorators');
const web = require('moleculer-web');
const broker = new moleculer.ServiceBroker({
logger: console,
logLevel: "debug",
});
@Service({
mixins: [web],
settings: {
port: 3000,
routes: [
//...
]
}
})
class MyService {
@Action()
Login(ctx) {
//...
}
// With options
@Action({
cache: false,
params: {
a: "number",
b: "number"
}
})
Login2(ctx) {
//...
}
@Event
'event.name'(payload, sender, eventName) {
//...
}
@Method
authorize(ctx, route, req, res) {
//...
}
hello() { // Private
//...
}
started() { // Reserved for moleculer, fired when started
//...
}
created() { // Reserved for moleculer, fired when created
//...
}
stopped() { // Reserved for moleculer, fired when stopped
//...
}
}
broker.createService(MyService);
broker.start();