Bookworm, Programmer

Just log

30 Jul 2017

What’s log


A record of a journey made by a ship or aircraft, detailing all events, or the book in which it is kept

(Computers) Any of various chronological records made concerning the use of a computer system, the changes made to data, etc.

Why Log are important

  • Compliance and regulations: Provide an audit trail of who, what, where, when and why
  • Situational awareness
  • Incident reponse
  • Real time alerts

Key point of log

  • Timestamp
  • Sequence
  • Meaningful
  • Format of records + Contents
  • Immutable
  • Structured vs Unstructured

Log Level

  • Debug: Used only for development and testing. Temporary open on production to find more information. (Caution with the log size)
  • Information: Used to keep the information that is useful for system runningandmanagement. Theentryandexitpointsofkeyfunctions should be kept in this level.
  • Warning: Used to keep the handled exceptions or other important log events.
  • Error: Used to keep the unhandled exceptions
  • Fatal: Reserved for special exceptions/conditions that need to be taken care of.

Sample of logs

  • History Record

BC1667 Prometheus is chained to the Scythian rocks after stealing the secret of fire from the Gods and giving it to man

– from Timeline of Greek Myth

  • Quest Log (Game)

Quest Log

  • Black box flight recording

Black Box Flight Recorder

  • Operation Log (Computer)

Operation log all

  • Application Log (Computer)

application log

What to log

The logs are often met

  • Transaction Log/Binlog
  • Operation Log
  • ApplicationLog

Operation log

  • Purpose
  • Keep the track of what user had done + For AUDIT
  • For Track of record change
  • Key elements
  • When - Timestamp
  • Who - User
  • What - what was did
  • Where - IP/Host
  • Identifier - Table(moudle) Name, record_id

Application log

  • Purpose
  • Keep necessary application running information + For online problem analysis
  • For debug
  • Key elements
  • When - Timestamp
  • What
    • LogLevel
    • (Error)Message
    • Stacktrace
  • Where–Host/IP
  • Secure–removesensitiveinformation + Centralize

Metric log

  • Purpose
  • Keep Application running stat, mainly numbers about business + Monitor
  • Alert
  • Key element
  • When – Timestamp
  • Who – App Identifier
  • Where – Host/IP/Tags
  • What - Metrics

Trace Log

  • Purpose
  • An unique Id to link the logs in different application + Generatedattheverybeginningattherequest
  • Saveineverylogsasafieldoratag
  • Onlineproblemanalysis + User behavior tracking
  • Key Elements
  • What – unique tracke Id in other log + Others – almost the same as

How to log

how to use log

The Usages of Log

  • Metrics for monitor and alert
  • Where alerts rings, go to application log for detail information + Use trace to find association logs in other app is necessary
  • Prediction

A few log systems

  • ELK – Metrics, application log etc
  • Statsd+Grafana / statsd + graphite – Metrics
  • Splunk – commercial
  • Customized


  • Careful choose log level
  • Centralize the logs
  • Secure the logs
  • Do Log
  • Do Use the log:
    • Monitor & Alert
    • Analysis the logs