Logger

In Moleculer project every main module has a custom logger instance. They inherit it from the broker logger instance which you can set in the broker options.

It supports also external loggers like Pino, Bunyan, Winston, …etc.

Built-in logger

The Moleculer has a built-in console logger. You can enable it with logger: console or logger: true options.

Built-in console logger:

let { ServiceBroker } = require("moleculer");
let broker = new ServiceBroker({
    logger: console,
    logLevel: "info"
});

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

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

Console messages:

[2017-08-18T12:37:25.714Z] INFO  dev-pc/POSTS: Log message via Service logger
[2017-08-18T12:37:25.718Z] INFO  dev-pc/BROKER: Log message via Broker logger
[2017-08-18T12:37:25.720Z] INFO  dev-pc/BROKER: Broker stopped.

Custom log levels

You can change the log level with logLevel option in broker options. You can use it with built-in console logger only.

let 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

Custom log formats

You can set a custom log formatter function for the built-in logger.

const broker = new ServiceBroker({ 
    logger: console, 
    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

You can 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({ 
    logger: console, 
    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

You can use external loggers with Moleculer. In this case you can 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 broker = new ServiceBroker({ 
    logger: bindings => new winston.Logger({
        transports: [
            new (winston.transports.Console)({
                timestamp: true,
                colorize: true,
                prettyPrint: true
            })
        ]
    })
});

Winston context

const WinstonContext = require("winston-context");
const winston = require("winston");
const broker = createBroker({ 
    logger: bindings => new WinstonContext(winston, "", bindings)
});

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

const WinstonContext = require("winston-context");
const winston = require("winston");
const { extend } = require("moleculer").Logger;
const broker = createBroker({ 
    logger: bindings => extend(new WinstonContext(winston, "", 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!