Bunyan https://github.com/trentm/node-bunyan
Bunyan is a simple and fast JSON logging library for node.js services:
var bunyan = require('bunyan');
var log = bunyan.createLogger({name: "myapp"});
log.info("hi");
and a bunyan CLI tool for nicely viewing those logs:
Manifesto: Server logs should be structured. JSON's a good format. Let's do that. A log record is one line of JSON.stringify'd output. Let's also specify some common names for the requisite and common fields for a log record (see below).
Current Status
Bunyan supports node 0.6 and greater.
npm install bunyan
Tip: The bunyan CLI tool is written to be compatible (within reason) with all versions of Bunyan logs. Therefore you might want to npm install -g bunyan to get the bunyan CLI on your PATH, then use local bunyan installs for node.js library usage of bunyan in your apps.
- elegant log method API
- extensible streams system for controlling where log records go (to a stream, to a file, log file rotation, etc.)
-
bunyanCLI for pretty-printing and filtering of Bunyan logs - simple include of log call source location (file, line, function) with
src: true - light-weight specialization of Logger instances with
log.child - custom rendering of logged objects with "serializers"
- Runtime log snooping via Dtrace support
Like most logging libraries you create a Logger instance and call methods named after the logging levels:
$ cat hi.js
var bunyan = require('bunyan');
var log = bunyan.createLogger({name: 'myapp'});
log.info('hi');
log.warn({lang: 'fr'}, 'au revoir');
All loggers must provide a "name". This is somewhat akin to the log4j logger "name", but Bunyan doesn't do hierarchical logger names.
Bunyan log records are JSON. A few fields are added automatically: "pid", "hostname", "time" and "v".
$ node hi.js
{"name":"myapp","hostname":"banana.local","pid":40161,"level":30,"msg":"hi","time":"2013-01-04T18:46:23.851Z","v":0}
{"name":"myapp","hostname":"banana.local","pid":40161,"level":40,"lang":"fr","msg":"au revoir","time":"2013-01-04T18:46:23.853Z","v":0}
The example above shows two different ways to call log.info(...). The full API is:
log.info(); // Returns a boolean: is the "info" level enabled?
// This is equivalent to `log.isInfoEnabled()` or
// `log.isEnabledFor(INFO)` in log4j.
log.info('hi'); // Log a simple string message (or number).
log.info('hi %s', bob, anotherVar); // Uses `util.format` for msg formatting.
log.info({foo: 'bar'}, 'hi');
// Adds "foo" field to log record. You can add any number
// of additional fields here.
log.info(err); // Special case to log an `Error` instance to the record.
// This adds an "err" field with exception details
// (including the stack) and sets "msg" to the exception
// message.
log.info(err, 'more on this: %s', more);
// ... or you can specify the "msg".
Note that this implies you cannot pass any object as the first argument to log it. IOW, log.info(mywidget) may not be what you expect. Instead of a string representation of mywidget that other logging libraries may give you, Bunyan will try to JSON-ify your object. It is a Bunyan best practice to always give a field name to included objects, e.g.:
log.info({widget: mywidget}, ...)
This will dove-tail with Bunyan serializer support, discussed later.
The same goes for all of Bunyan's log levels: log.trace, log.debug, log.info, log.warn, log.error, and log.fatal. See the levels section below for details and suggestions.
Bunyan log output is a stream of JSON objects. This is great for processing, but not for reading directly. A bunyan tool is provided for pretty-printing bunyan logs and for filtering (e.g. | bunyan -c 'this.foo == "bar"'). Using our example above:
$ node hi.js | ./bin/bunyan
[2013-01-04T19:01:18.241Z] INFO: myapp/40208 on banana.local: hi
[2013-01-04T19:01:18.242Z] WARN: myapp/40208 on banana.local: au revoir (lang=fr)
See the screenshot above for an example of the default coloring of rendered log output. That example also shows the nice formatting automatically done for some well-known log record fields (e.g. req is formatted like an HTTP request, res like an HTTP response, err like an error stack trace).
One interesting feature is filtering of log content, which can be useful for digging through large log files or for analysis. We can filter only records above a certain level:
$ node hi.js | bunyan -l warn
[2013-01-04T19:08:37.182Z] WARN: myapp/40353 on banana.local: au revoir (lang=fr)
Or filter on the JSON fields in the records (e.g. only showing the French records in our contrived example):
$ node hi.js | bunyan -c 'this.lang == "fr"'
[2013-01-04T19:08:26.411Z] WARN: myapp/40342 on banana.local: au revoir (lang=fr)
See bunyan --help for other facilities.
Other Tools
winston https://github.com/flatiron/winston
Make apache log in json http://cookbook.logstash.net/recipes/apache-json-logs/