kubelogger

Quick logger for apps running inside Kubernetes containers.

A Kubelogger is a qlogger that is wired to convert all output to K8s compatible json bundles and write them to the process stdout. Different log streams can be distinguished by their type. All kubelogger output is written to stdout as newline terminated json bundles. Each bundle has fields time and type, plus the message.

Kubelogger is an object logger where ideally each message is an object. Already serialized objects will be logged as strings, and will get doubly stringified.

Quick Start

    const kubelogger = require('kubelogger');

    const appLogger = kubelogger('debug', 'MyApp');
    appLogger.info('app running');
    // => {"time":"2019-02-05T20:15:45.830Z","type":"MyApp","message":"app running"}

    const consoleLogger = kubelogger('info', 'console')
        .captureWrites(process.stdout)
        .captureWrites(process.stderr);
    console.log('Hello, world.');
    process.stderr.write('Oops!');
    // => {"time":"2019-02-05T20:13:13.240Z","type":"console","message":"Hello, world.\n"}
    // => {"time":"2019-02-05T20:13:13.241Z","type":"console","message":"Oops!\n"}

API

logger = kubelogger( loglevel, type )

Create a new logger. The default loglevel is 'info', the default type 'undefined'.

The logger is instanceof qlogger with a predefined filter to convert all log messages into json bundles, and a predefined writer to write the bundle to the process stdout. Note that unlike an ordinary qlogger, a kubelogger will apply its built-in serializer filter as the last filtering step even if other filters are added.

The json bundles have properties time, type and message. Time is formatted like Date.toISOString(), but much faster (faster than String(Date.now()); faster even than String(count++)). Type is as received by the constructor. The message is the JSON stringified string or object being logged.

    const logger = kubelogger('info', 'example');
    logger.info('test');
    // => {"time":"2019-02-05T20:13:14.481Z","type":"example","message":"test\n"}
    logger.warn({ code: 'green', ok: 1 });
    // => {"time":"2019-02-05T20:13:14.482Z","type":"example","message":{"code":"green","ok":1}}

logger.captureWrites( stream )

Convert all writes to the given stream into log messages sent to this logger. Log message formatting and output is handled as described above. Only one logger can capture a stream at a time; the most recent capture will get the data.

The written data must be 'string' or 'Buffer', object mode is not supported and throws a TypeError. Buffers are converted to utf8 and are logged as text. The assumption is that Buffers contain complete log messages not binary data, so utf8 chars split across data chunks will not work right.

If the stream being captured is process.stderr, any global uncaughtException events will also be converted and written to the stream. Because of the way uncaughtException works, if there are no other uncaughtException listeners kubelogger will rethrow the fatal error to maintain the default behavior and stop the program; if there are others, it leaves it up to them to decide.

    const logger = kubelogger('info', 'stdout').captureWrites(process.stdout);
    console.log('gotcha!');
    // => {"time":"2019-02-05T20:13:14.483Z","type":"stdout","message":"gotcha!\n"}

logger.restoreWrites( stream )

Undo a captureWrites, restore normal write behavior on the stream. Not normally needed inside a container, but is useful for testing, and just in case.

logger.close( callback )

Flush pending output, restore the captured writes, and invoke callback with any deferred logging error(s). Call when exiting the app to not leave unwritten messages in the buffers.

Change Log

• 0.9.4 - upgrade qlogger for node-v12
• 0.9.3 - capture and write uncaught global exceptions, stringify type
• 0.9.2 - expose the QLogger and filters used, make addFilter work right
• 0.9.1 - upgrade qlogger
• 0.9.0 - first version

Related Work

qlogger