microservice chain logger
Text or JSON-formatted logger for microservices
with bundled Correlation ID and http-server access logging.
Features:
- wrappers for
console.info/warn/error
producing a text or JSON inflated with customizable metadata - access log express middleware for providing metadata through the same API
- reading/assigning
X-Correlation-ID
which is automatically reflected in the log messages (including access logs)
All of the features are optional and you can use only the ones you need.
Install
npm install microservice-chain-logger
Basic example
const logger = require('microservice-chain-logger');
const app = require('express')();
app.use(logger.initAccessLog(
useJsonTransformer: true
));
app.get('/', (req, res) => {
logger.info(req, 'root called with headers', req.headers);
res.send('Hello World');
});
app.use((err, req, res, next) => {
logger.error(req, 'there was an error:', err);
next();
});
app.listen(3000);
logger.info('call: curl http://localhost:3000/');
Please note that the logger is a singleton meaning
any changes you make to it by replacing a function would
have immediate effect on the entire application.
API
logger.info(), logger.warn(), logger.error(), logger.info()
These functions correspond to console
but also add metadata,
e.g. processTime
, correlationId
and any other data you inject
using transformEntry
.
The first parameter has a special meaning. If it's an instance
of express Request, then it's not logged but used as a context,
e.g. as a source for correlationId
app.get('/some/route', (req, res) => {
logger.info('just some text');
logger.warn('you', {can: 'mix'}, 'different', ['types', 1337]);
logger.info(req, 'message with meta data', {from: 'the req'});
});
Not logger.info() uses the same console.info() just like logger.info()
logger.infoSource()
Same as logger.info() but adds file, line and column fields referencing
the code location where it was called
logger.infoSource('reached this point!');
logger.initAccessLog(opts)
- opts -
Object
or undefined
The access log can be used as a replacement for the morgan
module,
keeping all of the logs in a consistent format and implicitly providing correlationId
for each request.
The request duration is automatically measured and stored
in the duration field.
The access log middleware adds a field isAccessLog
to the log
entry, which is then removed in the default transformEntry
.
You can use this flag for special logic for messages coming from access log.
app.get('/status', (req, res) => res.send('healthy'));
app.use(logger.initAccessLog());
app.get('/', (req, res) => {
res.send('requests to this and further routes will be logged');
});
The only supported option
is useJsonTransformer, which is a shortcut for replacing
transformEntry with jsonTransformer function.
app.use(logger.initAccessLog({
useJsonTransformer: process.env.NODE_ENV === 'production'
}));
logger.getCorrelationId(req)
Returns the value of X-Correlation-ID
if provided in the header,
otherwise creates a new one using UUID v4.
app.get('/', (req, res) => {
res.send('correlationId is ' + logger.getCorrelationId(req));
});
logger.assignCorrelationId(req, opts)
Assigns correlationId
to request
-compatible opts
-object.
If a new correlation ID was generated then it's also assigned
to the current req
. This ensures that it appears in all
subsequent log messages and eventually in the access log.
app.get('/', (req, res) => {
res.send('correlationId is ' + logger.getCorrelationId(req));
});
Hacking API
For most of the cases you should be fine with functions above,
but feel free to hack the library at your on risk.
logger.transformEntry(func, entry)
Params:
- func - console logging function such as
console.info/warn/error
- entry - the object containing the message and metadata to be logged
Returns String
or undefined
.
Returning undefined
skips the current message.
Replacing this function allows customizing the log format
and log filtering. By default a text transformer is used (logger.textTransformer).
The text transformer supports displaying the following fields:
- processTime
- message
- stack
- file, line, column
- duration
logger.transformEntry = loger.jsonTransformer;
logger.transformEntry = (func, entry) => {
if (!entry.isAccessLog && func === console.info) {
return;
}
return entry.processTime + ' ' + entry.message;
};
logger.makeEntry(req, ...messages)
Params:
- req - express Request or
null
- ...messages - mixed
Returns Object
.
Replacing this function allows you to alter metadata injection,
on the step BEFORE transformEntry
, e.g. if you want to inject
something from req
other than just correlationId
const origianlMakeEntry = logger.makeEntry;
logger.makeEntry = (req, ...messages) => {
const result = origianlMakeEntry(req, ...messages);
if (req) {
result.method = req.method;
}
return result;
};
logger.applyLogFunction(func, entry)
Params:
- func - one of the loging functions:
console.info
, console.warn
or console.error
- entry - message object
The unferlying function for logger.info/warn/error
working with the logging object instead of trying to format mixed parameters
as a single message string. It will NOT call makeEntry
, so if you need
the context just call makeEntry
explicitly to prepare the initial entry.
You can use it to inject specific custom fields directly from your code.
Most likely you want to set at least message and processTime
properties to keep it consistent with the rest of the library.
logger.applyLogFunction(console.info, {
message: "balloon started",
color: "blue",
size: "medium",
processTime: (new Date()).toISOString()
});
... and yes, you can replace it to match you needs just like other functions above
Using together with kraken.js
Here is a sample of how you can replace the standard morgan access log just by changing the config:
{
"middleware": {
"logger": {
"route": "/((?!metrics|status|favico.ico|robots.txt))*",
"priority": 0,
"module": {
"name": "microservice-chain-logger",
"method": "initAccessLog",
"arguments": [
{
"useTextTransformer": true
}
]
}
}
}
}
... you may want to move the arguments
part to development.json
,
so that in production you get JSON.
More examles
See more advanced examples on github:
License
MIT