Networking

In order to communicate with other nodes (ServiceBrokers) you need to configure a transporter. Most of the supported transporters connect to a central message broker that provide a reliable way of exchanging messages among remote nodes. These message brokers mainly support publish/subscribe messaging pattern.

Networking diagram

Transporters

Transporter is an important module if you are running services on multiple nodes. Transporter communicates with other nodes. It transfers events, calls requests and processes responses …etc. If multiple instances of a service are running on different nodes then the requests will be load-balanced among them.

The whole communication logic is outside of transporter class. It means that you can switch between transporters without changing any line of code.

There are several built-in transporters in Moleculer framework.

TCP transporter

Stable transporter
This is a no-dependency, zero-configuration TCP transporter. It uses Gossip protocol to disseminate node statuses, service list and heartbeats. It contains an integrated UDP discovery feature to detect new and disconnected nodes on the network.
If the UDP is prohibited on your network, use urls option. It is a list of remote endpoints (host/ip, port, nodeID). It can be a static list in your configuration or a file path which contains the list.

Use TCP transporter with default options

// moleculer.config.js
module.exports = {
transporter: "TCP"
};

All TCP transporter options with default values

// moleculer.config.js
module.exports = {
logger: true,
transporter: {
type: "TCP",
options: {
// Enable UDP discovery
udpDiscovery: true,
// Reusing UDP server socket
udpReuseAddr: true,

// UDP port
udpPort: 4445,
// UDP bind address (if null, bind on all interfaces)
udpBindAddress: null,
// UDP sending period (seconds)
udpPeriod: 30,

// Multicast address.
udpMulticast: "239.0.0.0",
// Multicast TTL setting
udpMulticastTTL: 1,

// Send broadcast (Boolean, String, Array<String>)
udpBroadcast: false,

// TCP server port. Null or 0 means random port
port: null,
// Static remote nodes address list (when UDP discovery is not available)
urls: null,
// Use hostname as preffered connection address
useHostname: true,

// Gossip sending period in seconds
gossipPeriod: 2,
// Maximum enabled outgoing connections. If reach, close the old connections
maxConnections: 32,
// Maximum TCP packet size
maxPacketSize: 1 * 1024 * 1024
}
}
};

TCP transporter with static endpoint list

// moleculer.config.js
module.exports = {
nodeID: "node-1",
logger: true,
transporter: {
type: "TCP",
options: {
udpDiscovery: false,
urls: [
"172.17.0.1:6000/node-1",
"172.17.0.2:6000/node-2",
"172.17.0.3:6000/node-3"
],
}
}
};

You don’t need to set port because it find & parse the self TCP port from URL list.

TCP transporter with shorthand static endpoint list
It needs to start with tcp://.

// moleculer.config.js
module.exports = {
nodeID: "node-1",
transporter: "tcp://172.17.0.1:6000/node-1,172.17.0.2:6000/node-2,172.17.0.3:6000/node-3"
};

TCP transporter with static endpoint list file

// moleculer.config.js
module.exports = {
nodeID: "node-1",
transporter: "file://./nodes.json"
};
// nodes.json
[
"127.0.0.1:6001/client-1",
"127.0.0.1:7001/server-1",
"127.0.0.1:7002/server-2"
]
Serviceless node

Please note, you don’t need to list all remote nodes. It’s enough at least one node which is online. For example, create a “serviceless” gossiper node, which does nothing, just shares other remote nodes addresses by gossip messages. So all nodes must know only the gossiper node address to be able to communicate with all other nodes.

NATS Transporter

Stable transporter
Built-in transporter for NATS.

NATS Server is a simple, high performance open source messaging system for cloud-native applications, IoT messaging, and microservices architectures.

// moleculer.config.js
module.exports = {
nodeID: "server-1",
transporter: "nats://nats.server:4222"
};
Dependencies

To use this transporter install the nats module with npm install nats --save command.

Examples

Connect to ‘nats://localhost:4222’

// moleculer.config.js
module.exports = {
transporter: "NATS"
};

Connect to a remote NATS server

// moleculer.config.js
module.exports = {
transporter: "nats://nats-server:4222"
};

Connect with options

// moleculer.config.js
module.exports = {
transporter: {
type: "NATS",
options: {
url: "nats://localhost:4222"
user: "admin",
pass: "1234"
}
}
};

Connect with TLS

// moleculer.config.js
module.exports = {
transporter: {
type: "NATS",
options: {
url: "nats://localhost:4222"
// More info: https://github.com/nats-io/node-nats#tls
tls: {
key: fs.readFileSync('./client-key.pem'),
cert: fs.readFileSync('./client-cert.pem'),
ca: [ fs.readFileSync('./ca.pem') ]
}
}
}
};

Redis Transporter

Stable transporter
Built-in transporter for Redis.

// moleculer.config.js
module.exports = {
nodeID: "server-1",
transporter: "redis://redis.server:6379"
};
Dependencies

To use this transporter install the ioredis module with npm install ioredis --save command.

Examples

Connect with default settings

// moleculer.config.js
module.exports = {
transporter: "Redis"
};

Connect with connection string

// moleculer.config.js
module.exports = {
transporter: "redis://localhost:6379"
};

Connect to a secure Redis server

// moleculer.config.js
module.exports = {
transporter: "rediss://localhost:6379"
};

Connect with options

// moleculer.config.js
module.exports = {
transporter: {
type: "Redis",
options: {
host: "redis-server",
db: 0
}
}
};

Connect to Redis cluster

// moleculer.config.js
module.exports = {
transporter: {
type: "Redis",
options: {
cluster: {
nodes: [
{ host: "localhost", port: 6379 },
{ host: "localhost", port: 6378 }
]
}
}
}
};

MQTT Transporter

Stable transporter
Built-in transporter for MQTT protocol (e.g.: Mosquitto).

// moleculer.config.js
module.exports = {
nodeID: "server-1",
transporter: "mqtt://mqtt-server:1883"
};
Dependencies

To use this transporter install the mqtt module with npm install mqtt --save command.

Examples

Connect with default settings

// moleculer.config.js
module.exports = {
transporter: "MQTT"
};

Connect with connection string

// moleculer.config.js
module.exports = {
transporter: "mqtt://mqtt-server:1883"
};

Connect to secure MQTT server

// moleculer.config.js
module.exports = {
transporter: "mqtts://mqtt-server:1883"
};

Connect with options

// moleculer.config.js
module.exports = {
transporter: {
type: "MQTT",
options: {
host: "mqtt-server",
port: 1883,
qos: 0,
topicSeparator: "."
}
}
};

AMQP (0.9) Transporter

Stable transporter
Built-in transporter for AMQP 0.9 protocol (e.g.: RabbitMQ).

// moleculer.config.js
module.exports = {
nodeID: "server-1",
transporter: "amqp://rabbitmq-server:5672"
};
Dependencies

To use this transporter install the amqplib module with npm install amqplib --save command.

Transporter options

Options can be passed to amqp.connect() method.

Connect to ‘amqp://guest:[email protected]:5672’

// moleculer.config.js
module.exports = {
transporter: "AMQP"
});

Connect to a remote server

// moleculer.config.js
module.exports = {
transporter: "amqp://rabbitmq-server:5672"
});

Connect to a secure server

// moleculer.config.js
module.exports = {
transporter: "amqps://rabbitmq-server:5672"
});

Connect to a remote server with options & credentials

// moleculer.config.js
module.exports = {
transporter: {
type: "AMQP",
options: {
url: "amqp://user:[email protected]:5672",
eventTimeToLive: 5000,
prefetch: 1,
socketOptions: {
servername: process.env.RABBIT_SERVER_NAME
}
// If true, queues will be autodeleted once service is stopped, i.e., queue listener is removed
autoDeleteQueues: true
}
}
};

AMQP 1.0 Transporter

Experimental transporter
Built-in transporter for AMQP 1.0 protocol (e.g.: ActiveMq or RabbitMQ + rabbitmq-amqp1.0 plugin).

Please note, it is an experimental transporter. Do not use it in production yet!

// moleculer.config.js
module.exports = {
transporter: "amqp10://activemq-server:5672"
};
Dependencies

To use this transporter install the rhea-promise module with npm install rhea-promise --save command.

Transporter options

Options can be passed to rhea.connection.open() method, the topics, the queues, and the messages themselves.

Connect to ‘amqp10://guest:[email protected]:5672’

// moleculer.config.js
module.exports = {
transporter: "AMQP10"
};

Connect to a remote server

// moleculer.config.js
module.exports = {
transporter: "amqp10://activemq-server:5672"
};

Connect to a remote server with options & credentials

// moleculer.config.js
module.exports = {
transporter: {
url: "amqp10://user:[email protected]:5672",
eventTimeToLive: 5000,
heartbeatTimeToLive: 5000,
connectionOptions: { // rhea connection options https://github.com/amqp/rhea#connectoptions, example:
ca: "", // (if using tls)
servername: "", // (if using tls)
key: "", // (if using tls with client auth)
cert: "" // (if using tls with client auth)
},
queueOptions: {}, // rhea queue options https://github.com/amqp/rhea#open_receiveraddressoptions
topicOptions: {}, // rhea queue options https://github.com/amqp/rhea#open_receiveraddressoptions
messageOptions: {}, // rhea message specific options https://github.com/amqp/rhea#message
topicPrefix: "topic://", // RabbitMq uses '/topic/' instead, 'topic://' is more common
prefetch: 1
}
};

Kafka Transporter

Stable transporter
Built-in transporter for Kafka.

It is a simple implementation. It transfers Moleculer packets to consumers via pub/sub. There are not implemented offset, replay…etc features.

Dependencies

To use this transporter install the kafka-node module with npm install kafka-node --save command.

Connect to Zookeeper

// moleculer.config.js
module.exports = {
transporter: "kafka://192.168.51.29:2181"
};

Connect to Zookeeper with custom options

// moleculer.config.js
module.exports = {
transporter: {
type: "kafka",
options: {
host: "192.168.51.29:2181",

// KafkaClient options. More info: https://github.com/SOHU-Co/kafka-node#clientconnectionstring-clientid-zkoptions-noackbatchoptions-ssloptions
client: {
zkOptions: undefined,
noAckBatchOptions: undefined,
sslOptions: undefined
},

// KafkaProducer options. More info: https://github.com/SOHU-Co/kafka-node#producerclient-options-custompartitioner
producer: {},
customPartitioner: undefined,

// ConsumerGroup options. More info: https://github.com/SOHU-Co/kafka-node#consumergroupoptions-topics
consumer: {
},

// Advanced options for `send`. More info: https://github.com/SOHU-Co/kafka-node#sendpayloads-cb
publish: {
partition: 0,
attributes: 0
}
}
}
};

NATS Streaming (STAN) Transporter

Stable transporter
Built-in transporter for NATS Streaming.

It is a simple implementation. It transfers Moleculer packets to consumers via pub/sub. There are not implemented offset, replay…etc features.

// moleculer.config.js
module.exports = {
nodeID: "server-1",
transporter: "stan://nats-streaming-server:4222"
};
Dependencies

To use this transporter install the node-nats-streaming module with npm install node-nats-streaming --save command.

Examples

Connect with default settings

// moleculer.config.js
module.exports = {
transporter: "STAN"
};

Connect with connection string

// moleculer.config.js
module.exports = {
transporter: "stan://nats-streaming-server:4222"
};

Connect with options

// moleculer.config.js
module.exports = {
transporter: {
type: "STAN",
options: {
url: "stan://127.0.0.1:4222",
clusterID: "my-cluster"
}
}
};

Custom transporter

Custom transporter module can be created. We recommend to copy the source of NatsTransporter and implement the connect, disconnect, subscribe and send methods.

Create custom transporter

const BaseTransporter = require("moleculer").Transporters.Base;

class MyTransporter extends BaseTransporter {
connect() { /*...*/ }
disconnect() { /*...*/ }
subscribe() { /*...*/ }
send() { /*...*/ }
}

Use custom transporter

// moleculer.config.js
const MyTransporter = require("./my-transporter");

module.exports = {
transporter: new MyTransporter()
};

Disabled balancer

Some transporter servers have built-in balancer solution. E.g.: RabbitMQ, NATS, NATS-Streaming. If you want to use the transporter balancer instead of Moleculer balancer, set the disableBalancer broker option to true.

Example

// moleculer.config.js
module.exports = {
disableBalancer: true,
transporter: "nats://some-server:4222"
};
Please note

If you disable the built-in Moleculer balancer, all requests & events will be transferred via transporter (including local requests). E.g. you have a local math service and you call math.add locally, the request will be sent via transporter.

Serialization

Transporter needs a serializer module which serializes & deserializes the transferred packets. The default serializer is the JSONSerializer but there are several built-in serializer.

Example

// moleculer.config.js
module.exports = {
nodeID: "server-1",
transporter: "NATS",
serializer: "ProtoBuf"
};

JSON serializer

This is the default serializer. It serializes the packets to JSON string and deserializes the received data to packet.

// moleculer.config.js
module.exports = {
serializer: "JSON" // not necessary to set, because it is the default
};

Avro serializer

Built-in Avro serializer.

// moleculer.config.js
module.exports = {
serializer: "Avro"
};
Dependencies

To use this serializer install the avsc module with npm install avsc --save command.

MsgPack serializer

Built-in MsgPack serializer.

// moleculer.config.js
module.exports = {
serializer: "MsgPack"
};
Dependencies

To use this serializer install the msgpack5 module with npm install msgpack5 --save command.

Notepack serializer

Built-in Notepack serializer.

// moleculer.config.js
module.exports = {
serializer: "Notepack"
};
Dependencies

To use this serializer install the notepack module with npm install notepack.io --save command.

ProtoBuf serializer

Built-in Protocol Buffer serializer.

// moleculer.config.js
module.exports = {
serializer: "ProtoBuf"
};
Dependencies

To use this serializer install the protobufjs module with npm install protobufjs --save command.

Thrift serializer

Built-in Thrift serializer.

// moleculer.config.js
module.exports = {
serializer: "Thrift"
};
Dependencies

To use this serializer install the thrift module with npm install thrift --save command.

Custom serializer

Custom serializer module can be created. We recommend to copy the source of JSONSerializer and implement the serialize and deserialize methods.

Create custom serializer

const BaseSerializer = require("moleculer").Serializers.Base;

class MySerializer extends BaseSerializer {
serialize(obj, type) { /*...*/ }
deserialize(buf, type) { /*...*/ }
}

Use custom serializer

// moleculer.config.js
const MySerializer = require("./my-serializer");

module.exports = {
serializer: new MySerializer()
};