@goodware/logger
Winston3-based logging utility for Node
Last updated 2 months ago by dev-guy .
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Winston3-based console, file, and AWS CloudWatch logger with awesome sauce

npm

Documentation TBD

LogManager

Usage

It is possible for one nodeJS process to create multiple LogManager objects at the same time. This is useful if, say, independent libraries use LogManager with different logging levels and other settings. The only caveat is Winston's own flaw that results in the inability of two LogManager objects to associate different colors with the same level.

A Winston logger object for a particular category is acquired via new LogManager(...).loggers.get() or child(). Requesting a logger is optional since this class has logging methods (log(), error(), etc.), that accept an optional category name and use the default category if one is not provided.

Loggers do not use Winston's splat formatter. However, much more can be logged, such as objects, arrays, and errors including stack traces.

While a LogManager instance is active, uncaught exceptions and Promise rejections are logged using a category that is specified via the 'uncaughtCategory' options setting which defaults to 'uncaught.' The process is not terminated after logging uncaught exceptions.

Calling the asynchronous stop() method is recommended to flush log entries before the process exits.

When a log entry's level is 'error', the current stack trace is added to the to the 'stack' or 'logStack' meta key. This behavior is disabled via the 'logStack' meta tag.

Concepts

options

An object provided to the constructor. Options are described by optionsObject.

logger

A logger sends log entries to transports.

A logger has the following methods: manager, winstonLogger, ready, parent, child, get, ready, isLevelEnabled, log, default, and methods named for each level, such as info. Each logging-related method accepts four optional parameters: tags, message, extra, and category.

category

The name of a logger. The default category is specified via the 'defaultCategory' options setting and defaults to 'general.' Transport filtering (based on tags) is specified on a per-category basis.

log entry

An object that is sent to a transport. A log entry consists of meta and data.

meta

The top-level keys of a log entry. Meta keys contain scalar values except for tags and logTransports which are arrays. Meta keys are: timestamp, ms (elpased time between log entries), level, message, error, tags, category, code, statusCode, logGroupId, logDepth, commitSha, correlationId, operationId, requestId, tenantId, hostId, stage, version, service, stack, logStack, and logTransports.

data

The keys remaining in 'both' after meta keys are removed (see 'both' below)

level (severity)

Levels are associated with natural numbers. Per Winston's convention, a lower value indicates greater severity. Therefore, 0 represents the highest severity.

Levels and their colors can be specified via the second argument provided to the constructor using the same object that is provided when creating a Winston logger.

By default, LogManager uses Winston's default levels (aka npm log levels with the addition of two levels:

  1. 'more' is between 'info' and 'verbose' and has the color cyan
  2. 'db' is between 'verbose' and 'http' and has the color white
  3. Therefore, from highest to lowest severity, the levels are: error, warn, info, more, verbose, db, http, debug, and silly.

default level

When a level is not found in the provided tags, the default level, 'debug', is added to the tags. The default level is specified via the 'defaultLevel' options setting.

level methods

Methods that are named after levels, such as error(). The method log(tags, message, extra, category) is an alternative to the level methods. Level methods accept variant parameters. If the first parameter to a level method is an array, the parameter list is (tags, message, extra, category). Otherwise, it's (message, extra, category).

level filtering

A log entry is sent to a transport only when its severity level is equal to or greater than the transport's level.

logging context

tags, extra, and category

tag

Tags are logged as an array of strings. Tags are specified via a single string, an array of strings, or an object in which each key value is evaluated for truthiness. Tags are combined via the static method tags(a, b) where b's tags override a's tags.

tag and level

Tags are a superset of levels. A log entry's level is, by default, set to the tag with the highest severity. Level methods override this behavior such that the level associated with the method is chosen. The level can be specified via the logLevel meta tag. The level can also be modified via tag configuration.

meta tag

Some tags alter logging behavior. The tags' value (tags can be specified as an object) enables and disables the feature, based on their truthiness. Meta tags are not logged. Meta tag names start with 'log' and 'noLog.' Meta tags tags that start with noLog negate their corresponding meta tags. For example, {logStack: true} is identical to 'logStack'. {logStack: false} is identical to 'noLogStack.' Meta tag names are:

logLevel

Use the meta tag's value as a log entry's logging level

logStack

Whether to add the current stack to meta. When true, populates the 'stack' or the 'logStack' meta key. This is the default behavior when a log entry's level is 'error.'

tag filtering

Tags can be used for additional filtering on a per-transport basis. Tags that are named after severity levels do not participate in tag filtering. All tags are enabled by default. When a log entry's level is 'warn' or 'error', tags are enabled. This behavior can be overidden by the 'allowLevel' setting. Tags are enabled and disabled on a per-category basis. The 'default' category specifies the default behavior for unlisted categories.

The following example enables the tag 'sql' for only two categories: one and two. Category 'one' changes the level to 'more' and sends log entries only to the file and console transports. Category 'two' sends log entries to all transports.

  categories: {
    default: {
      tags: {
        sql: 'off', // Disable for all transports for all categories. Log entries with warn and error levels are logged.
      },
    },
    one: {
      tags: {
        sql: {
          // Fine-tune filtering for category 'one.' All of these keys are optional.
          allowLevel: 'off', // Enable tag filtering for all log entries regardless of their levels. 'off' is needed
            // because the default is 'warn' which causes all log entries with warn and error levels to be logged.
          level: 'more', // Set the log entry's level to 'more'
          // Log entries are sent to all transports by default (console, file, errorFile, cloudWatch). Each transport
          // can be overridden:
          file: 'verbose', // Send a log entry with the 'sql' tag to the file transport if the log entry's severity
            // level is equal to or greater than 'verbose'
          console: 'on', // Send a log entry with the 'sql' tag to the console transport
          other: 'off', // Do not send a log entry with the 'sql' tag to CloudWatch
        },
      },
    },
    two: {
      tags: {
        sql: 'on', // Send all log entries with the 'sql' tag to all transports for category two
      },
    },
  }

host id

Uniquely identifies the system that is running node

stage

Identifies the environment in which node is running, such as 'dev' or 'prod'

extra

An optional string, array, or object to log with message. Two 'extra' objects are combined via the static method extra(a, b) in which b's keys override a's keys if they overlap.

message

A scalar, array, or object to log. If an object is provided, its 'message' property is moved to meta and other properties can be copied to meta. The list of keys to copy to meta is altered via the 'metaKeys' options setting. Properties are copied to meta if their values are scalar and their names are specified in metaKeys.

both

message and 'extra' are shallow copied and combined into a new object called 'both.' If message's keys overlap with those in 'extra,' 'extra' is logged separately; both log entries will have the same logGroupId meta key value.

error

Errors can be provided via both, both.error, both.cause, and both.originalError. Error objects may also have these keys. All error objects are logged separately such that each log entry has the same logGroupId meta key value. The values of the error, cause, and originalError are set to the Error objects' message property and therefore do not, for example, contain stack traces. As Error objects are traversed, embedded error objects are also traversed and logged recursively. The logDepth meta key contains a number, starting from 0, that indicates the recursion depth from both.

transport

A transport sends log entries to one of the following destinations:

  • file

    Writes log entries with level equal to or higher than a specified level (defaults to 'info') to a file named category-timestamp.log.

  • errorFile

    Writes log entries with level equal to or higher than a specified level (defaults to 'error') to a file named category-error-timestamp.log. Log entries are also sent to the file transport.

  • cloudWatch

    Sends log entries to CloudWatch AWS service

  • console

    Writes log entries to the process's STDOUT filehandle

transport level

Use the 'categories' options setting to configure transports. It is not necessary to specify every category that is actually used. The 'default' category specifies the base configuration for all categories. For example:

categories: {
  default: { console: 'on', cloudWatch: 'info',
             file: 'default' },
  api: { console: 'off' },
}

Level filtering for each transport is configured via a level name, 'default,' 'on,' or 'off.' 'off' is the default. Each transport type treats 'on' slightly differently:

  • file: on -> info
  • errorFile: on -> error
  • cloudWatch: on -> warn
  • console: on -> info, off -> warn if file and cloudWatch are both off

console

The behavior of console transports is altered via the 'console' options setting.

When 'colors' is true, log entries sent to the console are colorized. To override the provided value, set the

CONSOLE_COLORS

environment variable such that blank, 0, and 'false' are false and all other values are true.

When 'data' is true, the maximum amount of information is sent to the console, including meta, data, embedded errors, overridden 'extra' properties objects, and stack traces. When it is false, a small set of meta keys are sent to the console with a log entry's message. To override the value for 'data', set the

CONSOLE_DATA

environment variable such that blank, 0, and 'false' are false and all other values are true.

file and errorFile

Log entries are written to files as JSON strings to a directory specified via the 'file' options setting. If no directory in the provided array does not exist and can be created, the file-related transports are disabled. File names contain the category and the date and hour of the local time when this object was instantiated. For error log files, '-error' is appended to the category. Files have the extension .log. An example file name is: uncaught-error-2020-07-18-18.log. Files are rotated and zipped on an hourly basis. The maximum number of archived log files defaults to 14 days and can be specified via the 'file' options setting.

cloudWatch

CloudWatch transports are configured with a log group name and an optional AWS region. Log entries are sent to CloudWatch as JSON strings. One LogManager instance uses the same stream name for all cloudWatch transports. The log group, on the other hand, can be specified on a per-category basis. The log stream name contains the date and time (including the millisecond) when LogManager was instantiated followed by the host id. Any errors that occur while sending log entries to CloudWatch are written to the console and to files named cloudwatch-error*.log if a file directory is specified.

If an AWS region is not specified, the environment variables are used in the following order:

  1. AWS_CLOUDWATCH_LOGS_REGION
  2. AWS_CLOUDWATCH_REGION
  3. AWS_DEFAULT_REGION

Begin/End/Error Execution Wrapper Functions

Utility functions for logging 'begin' and 'end' for common operations (database, http, etc.). Begin log entries are tagged with 'begin.' End log entries are tagged with 'end.' The operationId property is set added to both entries with the same uuid generated for the operation. If an exception is thrown, an error is logged.

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