Logs can be a dumb warehouse of debug statements or the enabler of a beautiful dashboard that tells the story of your app. Plan your logging platform from day 1: how logs are collected, stored and analyzed to ensure that the desired information (e.g. error rate, following an entire transaction through services and servers, etc) can really be extracted.

Bunyan

Use Bunyan to log structured records. Alternatively you can use pino.

Bunyan log records are JSON. A few fields are added automatically: “pid”, “hostname”, “time” and “v”.

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// Log with an optional 'fields' object as the first parameter
log.info({foo: 'bar', err: err}, 'some msg about this error');

Child Logger

Bunyan has a concept of a child logger to specialize a logger for a sub-component of your application, i.e. to create a new logger with additional bound fields that will be included in its log records. A child logger is created with log.child(...).

Bunyan has a concept of “serializer” functions to produce a JSON-able object from a JavaScript object, so you can easily do the following:

log.info({req: <request object>}, 'something about handling this request');

and have the req entry in the log record be just a reasonable subset of fields (or computed data about those fields).

收集渠道

1. 系统未捕获错误:

   1 2	process.on('uncaughtException', processErrorHandler); process.on('unhandledRejection', processErrorHandler);

2. 程序内 byLog 的输出

3. console.error

针对 Express 可做如下埋点:

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// 在所有路由最后，添加错误处理，必须同时含有四个参数
// http://expressjs.com/en/guide/error-handling.html
app.use(function(err, req, res, next) {  
    res.send({
        code: 500,
        message: `System Error! Please send serial number ${req.x_request_id} to administer`
    });
    byLog.error(err, null, {
        req_id: req.x_request_id
    });
});

Logging in Distributed Systems

Have an Application Instance Identifier

Use the name field in bunyan.

Always Use UTC Time

Adding correlation IDs

This ID has to be passed around in function calls, and it has to be sent to downstream services too.

Using Trace

https://trace.risingstack.com/

Never, ever log credentials, passwords or any sensitive information.

Logging in NPM modules

Use the debug module.

By default, it will not produce any output. To enable this logger, you have run your application with a special environment variable, called DEBUG.

DEBUG=my-namespace,express* node app.js

Once you do that, the debug module will come to life and will start producing log events for stdout.

References

1. How to Get Node.js Logging Right