@synanetics/logging

Logging setup for Google Cloud Logging - Provides a Moleculer JS logging class SynLogger and a utility function writeLogEntry for use outside of Moleculer JS applications.

Moleculer JS Usage

const { SessionContextStorageMiddlewareSchema, SynLogger } = require('@synanetics/logging');
// or
import { SessionContextStorageMiddlewareSchema, SynLogger } from '@synanetics/logging';

Context Middleware

For SynLogger to populate session tracing we need to follow the request context. To do this we provide the SessionContextStorageMiddlewareSchema Middleware. You can follow the guideance provided below or check the documentation (be sure to use the documentation for you current version of MoleculerJS).

Register the middleware inside moleculer.config.js

const { Middlewares } = require('moleculer');
Middlewares[SessionContextStorageMiddlewareSchema.name] = SessionContextStorageMiddlewareSchema;

then in the same file ensure the exported object property middlewares has the corresponding name registered.

...
middlewares: [..., SessionContextStorageMiddlewareSchema.name],
...

Be aware that SynLogger will still function without this middleware but it will be unable annotate the tracing data to log entries for context requests.

SynLogger

Our custom logger has less overhead from a configuration point of view, simply create a new instance of the logger and assign it to the logger property. It accepts any opts that are applicable to the MoleculerJS BaseLogger.

You can optionally force it's output for a given environment as either docker or gcp. That would be an inspected output vs structured json respectively.

As per the documentation the config logLevel property only applies built-in MoleculerJS loggers. To set the level in the logger the level property needs to be provided in the options. level can either be a string e.g. { level: 'debug' } or it can be a structured object with targeted log levels per service e.g. { level: { 'SERVICE_ABC': 'debug', 'SERVICE_XYZ': 'info', '**': 'warn' } }. It follows the pattern documented for builtin loggers.

moleculer.config.js

const logger = new SynLogger({
    level: 'fatal' | 'error' | 'warn' | 'info' | 'debug' | 'trace',
});
await logger.setOutput({
    environment: 'docker' | 'gcp', // will attempt environment detection if not present but fallback to 'docker'
    depth: number;  // default 5 applies only to 'docker' environment
});

For convenience a static initialiser has been provided:

const logger = await SynLogger.init({
    level: 'fatal' | 'error' | 'warn' | 'info' | 'debug' | 'trace',
    output: {
        environment: 'docker' | 'gcp', // will attempt environment detection if not present but fallback to 'docker'
        depth: number;  // default 5 applies only to 'docker' environment
    },
});

The intended use for the logger is that argument one will be a message string. Argument two as an optional context object:

this.logger.info('my message', {
    extra: 'data',
    for: {
        the: ['logEntry', 'to', 'contain'],
    },
});

consideration has been where the message is omitted, the below would log with a message of "message omitted":

const err = new Error('example');
this.logger.error(err);

this.logger.info({
    extra: 'data',
    for: {
        the: ['logEntry', 'to', 'contain'],
    },
});

To align SynLogger to match MoleculerJS built-in implementation that logger will collect any additional supplied arguments and output all captured arguments as a values entry.

this.logger.info('message', { example: 'data' }, ['logEntry'], 'some string');
// will output a context object like:
{ message: 'message', jsonPayload: { values: [{ example: 'data' }, ['logEntry'], 'some string'] } }

Function Usage

const { writeLogEntry } = require('@synanetics/logging');
// or
import { writeLogEntry } from '@synanetics/logging';

The function will just print to stdout using the structured logging format desired by GCP. Arguments:

• type - expects string being one of fatal, error, warn, info, debug, trace - unknown values will fallback to structured severity level of 'DEFAULT' but a value MUST be supplied
• message - expects a string message to represent your log entry - if omitted a message of "message omitted" is used
• context - expects an object of any shape

writeLogEntry(type: string, context: object);
writeLogEntry(type: string, message: string, context: object);
writeLogEntry(type: string, message: string, context: object, mode: 'human' | 'json');


writeLogEntry('info', 'my message', {
    extra: 'data',
    for: {
        the: ['logEntry', 'to', 'contain'],
    },
});

writeLogEntry('debug', {
    extra: 'data',
    for: {
        the: ['logEntry', 'to', 'contain'],
    },
});

const err = new Error('example');

writeLogEntry('error', err);

writeLogEntry('fatal', 'critical error trying to do something important', err);

// would ouput:
// {YYYY-MM-DD HH:mm} [SEVERITY] message
//  indented pretty printed data..
//
writeLogEntry('fatal', 'critical error trying to do something important', { something: 'here' }, 'human');