Logging

In Moleculer framework all core modules have a custom logger instance. They are inherited from the broker logger instance which can be configured in the broker options.

Built-in logger

The Moleculer has a built-in console logger. It is the default logger.

Built-in console logger:

const { ServiceBroker } = require("moleculer");
const broker = new ServiceBroker({
    nodeID: "node-100",
    // logger: true,
    logLevel: "info"
});

broker.createService({
    name: "posts",
    actions: {
        get(ctx) {
            this.logger.info("Log message via Service logger");
        }
    }
});

broker.start()
    .then(() => broker.call("posts.get"))
    .then(() => broker.logger.info("Log message via Broker logger"));

Console messages:

[2018-06-26T11:38:06.728Z] INFO  node-100/POSTS: Log message via Service logger
[2018-06-26T11:38:06.728Z] INFO  node-100/BROKER: Log message via Broker logger
[2018-06-26T11:38:06.730Z] INFO  node-100/BROKER: ServiceBroker is stopped. Good bye.

Custom log levels

Log level can be changed with logLevel option in broker options. Use it with built-in console logger only.

const broker = new ServiceBroker({
    logger: true, // the `true` is same as `console`
    logLevel: "warn" // only logs the 'warn' & 'error' entries to the console
});

Available log levels: fatal, error, warn, info, debug, trace

Fine-tuned log levels

The log level can be set for every Moleculer module. Wildcard usage is allowed.

const broker = new ServiceBroker({
    logLevel: {
        "MY.**": false,         // Disable log
        "TRANS": "warn",        // Only 'warn ' and 'error' log entries
        "*.GREETER": "debug",   // All log entries
        "**": "info",           // All other modules use this level
    }
});

This settings are evaluated from top to bottom, so the ** level must be the last item.

Internal modules: BROKER, TRANS, TX as transporter, CACHER, REGISTRY.

For services, the name comes from the service name. E.g. POSTS. If version is defined it is used as prefix. E.g. V2.POSTS

Log formats

There are some built-in log formatter.

Name	Output
default	[2018-06-26T13:36:05.761Z] INFO node-100/BROKER: Message
simple	INFO - Message
short	[13:36:30.968Z] INFO BROKER: Message

Custom log formatter

Custom log formatter function can be set for the built-in console logger.

const broker = new ServiceBroker({ 
    logFormatter(level, args, bindings) {
        return level.toUpperCase() + " " + bindings.nodeID + ": " + args.join(" ");
    }
});
broker.logger.warn("Warn message");
broker.logger.error("Error message");

Output:

WARN dev-pc: Warn message
ERROR dev-pc: Error message

Custom object & array printing formatter

Set a custom formatter function to print object & arrays. The default function prints the objects & arrays to a single line in order to be easy to process with an external log tool. But when you are developing, it would be useful to print objects to a human-readable multi-line format. For this purpose, overwrite the logObjectPrinter function in the broker options.

Output with default function

[2017-08-18T12:37:25.720Z] INFO  dev-pc/BROKER: { name: 'node', lts: 'Carbon', sourceUrl: 'https://nodejs.org/download/release/v8.10.0/node-v8.10.0.tar.gz', headersUrl: 'https://nodejs.org/download/release/v8.10.0/node-v8.10.0-headers.tar.gz' }

Switch to multi-line printing & increment depth

const util = require("util");

const broker = new ServiceBroker({  
    logObjectPrinter: o => util.inspect(o, { depth: 4, breakLength: 100 })
});
broker.logger.warn(process.release);

Output:

[2017-08-18T12:37:25.720Z] INFO  dev-pc/BROKER: { name: 'node',
  lts: 'Carbon',
  sourceUrl: 'https://nodejs.org/download/release/v8.10.0/node-v8.10.0.tar.gz',
  headersUrl: 'https://nodejs.org/download/release/v8.10.0/node-v8.10.0-headers.tar.gz' }

External loggers

External loggers can be used with Moleculer. In this case, set a creator function to logger. The ServiceBroker will call it when a new module inherits a new logger instance.

Pino

const pino = require("pino")({ level: "info" });
const broker = new ServiceBroker({ 
    logger: bindings => pino.child(bindings)
});

Bunyan

const bunyan = require("bunyan");
const logger = bunyan.createLogger({ name: "moleculer", level: "info" });
const broker = new ServiceBroker({ 
    logger: bindings => logger.child(bindings)
});

Winston

const winston = require("winston");
const { extend } = require("moleculer").Logger;
const broker = new ServiceBroker({ 
    logger: bindings => extend(winston.createLogger({
        format: winston.format.combine(
            winston.format.label({ label: bindings }),
            winston.format.timestamp(),
            winston.format.json(),
        ),
        transports: [
            new winston.transports.Console()
        ]
    }))
});

Some external loggers have not trace & fatal log methods (e.g.: winston). In this case you have to extend your logger.

Bindings

The bindings object contains the following properties:

• ns - namespace
• nodeID - nodeID
• mod - type of core module: broker, cacher, transit, transporter
• svc - service name
• ver - service version

Please note

Avoid using these bindings property names when you log an Object.
For example: the broker.logger.error({ mod: "peanut" }) overrides the original mod value!