MSX Logging Module

MSX logging is an extension of the popular logrus logging library, to include:

• Log names
• Level-specific loggers
• Improved context handling

Usage

After importing the MSX log package, you can use the default named logger msx simply:

import "cto-github.cisco.com/NFV-BU/go-msx/log"

var logger = log.StandardLogger()

func main() {
    var action = "started"
    logger.Infof("Something happened: %s", action) 
}

To use a logger with a custom name:

var logger = log.NewLogger("alert.api")

To create a logger named after the current module:

var logger = log.NewPackageLogger()

To create a levelled logger, which outputs print at the defined log level:

debugLogger := logger.Level(log.DebugLevel)
debugLogger.Printf("Some template: %s", "inserted")

To record a golang error object:

func DeployResource(data []byte) {
    var body ResourceDeployment
    if err := json.Unmarshal(data, &body); err != nil {
        logger.
            WithError(err).
            Error("Failed to parse Resource Deployment request")
    }
}

To use the log context that was embedded in a Context object:

func HandleRequest(ctx context.Context) {
    requestLogger := logger.WithContext(ctx)
    ...
}

To add one-time custom diagnostic fields:

var logger = log.NewLogger("tenant")

func HandleGetTenantRequest(tenantId string) {
    logger.
        WithExtendedField("tenantId", tenantId).
        Debug("Tenant retrieval requested")
}

To create a sub-logger with custom diagnostic fields:

var logger = log.NewLogger("services.tenant")

func HandleGetTenantRequest(tenantId string) {
    requestLogger := logger.WithExtendedField("tenantId", tenantId)
    requestLogger.Debugf("some message")
}

Configuration

Logging Levels

MSX Logging defines the following log levels:

• Trace
• Debug
• Info
• Warn
• Error
• Panic
• Fatal

A logging level filter can be set globally:

log.SetLevel(log.WarnLevelName)

This will ensure all loggers not configured at a more strict level only output messages with a level of WARN or above.

An individual logger (and its sub-loggers) can be set to a minimum level:

logger = log.NewLogger("msx.beats")
logger.SetLevel(log.LevelByName(log.InfoLevelName)))

Configuration (eg. command line options) can be used to set a logger minimum level:

myapp --logger.msx.beats=debug

This will set the minimum level of the msx.beats logger tree to DEBUG after the application configuration has been loaded.

Output Format

Output can be switched to JSON formatting:

log.SetFormat(log.LogFormatJson)

And back to LogFmt formatting:

log.SetFormat(log.LogFormatLogFmt)

By default, all output is sent to standard output, with high-resolution timestamps. See init.go for specifics.