aah Logging

aah provides simple logger for real world application needs. It supports context, fields, console, file receivers, unified logger, child logger and drop-in replacement for standard logger.

Table of Contents

• Understanding aah Logging
• Context, Fields, Child Logger Since v0.9
• Human Readable and Machine Parsable Logging
• Unified Logging
• Logger Hook
• Log Configuration

Learn about Server Access Log and Server Dump Log.

Understanding aah Logging

aah initializes the application default logger based on configured values from log { ... } with context of Application Name and Application Instance Name.

Simply use Log methods -

• ctx.Log() - available on Controller : it log entry with context information such as appname, insname, reqid, principal.
• aah.AppLog() - application logger : use it for non request scenario’s.

func (a *AppController) MyAction(id string, info *models.MyModel) {

  // simply log it
  a.Log().Info("Welcome ", "to ", "aah ", "logger")
  a.Log().Infof("This is %s application logger", "example")

}

Composable Log Pattern

aah provides composable log pattern as follows. Note: log pattern is not applicable for JSON log. Since v0.9 appname, insname, reqid, principal flags supported.

Refer Log Configuration#Pattern

Context, Fields, Child Logger

Since v0.9 context, fields and child logger is supported.

• Context: You could create logger with context information via log.Fields values. Those values gets logged with every log entry.
  • aah.AppLog() - creates log entry with application name and application instance name
  • ctx.Log() - incoming request creates log entry with request id, user principal plus application context information such as app name and app instance name
• Fields: WithFields and WithField is used to log fields and values with current log entry.
• Child Logger: You can create child logger from existing aah logger instance. Upon creation it inherits parent logger context values once.
  • After creation, any changes to context value on parent or child does not affect each other.
  • All the log entries made by child logger; logged in parent receiver.
  • Child logger is handy when you want have logger per functionality/package/file, etc.
    • For example: you could create new child logger via aah.NewChildLogger(fields).

Human Readable and Machine Parsable Logging

aah supports both human readable and machine parseable log format.

Text log format

format = "text"

Example

2017-10-01 23:41:05.983 INFO  aahwebsite sfo-aahweb-01 aah go server running on :8080
2017-10-01 23:41:10.337 DEBUG aahwebsite sfo-aahweb-01 59d1df869bf2340ffaab2e28 Calling interceptor: DocController.Before
2017-10-01 23:41:10.338 DEBUG aahwebsite sfo-aahweb-01 59d1df869bf2340ffaab2e28 Calling controller: DocController.ShowDoc
2017-10-01 23:41:26.845 WARN  aahwebsite sfo-aahweb-01 Interrupt signal received
2017-10-01 23:41:26.846 DEBUG aahwebsite sfo-aahweb-01 Event [OnShutdown] publishing in synchronous mode
2017-10-01 23:41:26.846 INFO  aahwebsite sfo-aahweb-01 aah application shutdown successful

JSON log format

format = "json"

Example

{"level":"INFO","timestamp":"2017-10-01T23:41:52-07:00","app_name":"aahwebsite","instance_name":"sfo-aahweb-01","message":"aah go server running on :8080"}
{"level":"DEBUG","timestamp":"2017-10-01T23:42:00-07:00","app_name":"aahwebsite","instance_name":"sfo-aahweb-01","request_id":"59d1dfb89bf234103a1b35c2","message":"Calling interceptor: DocController.Before"}
{"level":"DEBUG","timestamp":"2017-10-01T23:42:00-07:00","app_name":"aahwebsite","instance_name":"sfo-aahweb-01","request_id":"59d1dfb89bf234103a1b35c2","message":"Calling controller: DocController.ShowDoc"}
{"level":"WARN","timestamp":"2017-10-01T23:42:50-07:00","app_name":"aahwebsite","instance_name":"sfo-aahweb-01","message":"Interrupt signal received"}
{"level":"DEBUG","timestamp":"2017-10-01T23:42:50-07:00","app_name":"aahwebsite","instance_name":"sfo-aahweb-01","message":"Event [OnShutdown] publishing in synchronous mode"}
{"level":"INFO","timestamp":"2017-10-01T23:42:50-07:00","app_name":"aahwebsite","instance_name":"sfo-aahweb-01","message":"aah application shutdown successful"}

Unified Logging

Typically aah user could be using many libraries with aah. Those might provide standard Go logger for logging. This is where unified logging shines.

Use log.ToGoLogger() to bind that logger with aah logger then you get unified logging at one place.

Logger Hook

Even though aah provides out-of-the-box JSON log format. You might need further extensibility to send your log entries to centralized logging system such as Kibana, Loggly, Splunk, etc.

Use Hook capability to register custom hooks. Hooks are executed in a goroutine and each hook receives log entry.

Example: Adding hook into aah application logger.

// Create logger Hook as type of `log.HookFunc`
func kibanaHook(e log.Entry) {
  // logger hook logic goes here.
}

func RegisterLoggerHooks(_ *aah.Event)  {
  aah.AddLoggerHook("kibana", kibanaHook)
  // so on ...
}

// Register it on <app-base-dir>/app/init.go file
func init() {
  aah.OnStart(myloggerhook.RegisterLoggerHooks)  
}