logrus

Logrus Logrus is a structured logger for Go (golang), completely API compatible with the standard library logger. Logrus is in maintenance mode. The project focuses on security, bug fixes, and performance improvements. New features are not planned, aside from changes required to provide interoperability with other logging ecosystems (e.g., Go's log/slog). I believe Logrus' biggest contribution is to have played a part in today's widespread use of structured logging in Golang. There doesn't seem to be a reason to do a major, breaking iteration into Logrus V2, since the fantastic Go community has built those independently. Many fantastic alternatives have sprung up. Logrus would look like those, had it been re-designed with what we know about structured logging in Go today. Check out, for example, Zerolog, Zap, and Apex. Nicely color-coded in development (when a TTY is attached, otherwise just plain text): With logrus.SetFormatter(&logrus.JSONFormatter{}), for easy parsing by logstash or Splunk: {"animal":"walrus","level":"info","msg":"A group of walrus emerges from the ocean","size":10,"time":"2014-03-10 19:57:38.562264131 -0400 EDT"} {"level":"warning","msg":"The group's number increased tremendously!","number":122,"omg":true,"time":"2014-03-10 19:57:38.562471297 -0400 EDT"} {"animal":"walrus","level":"info","msg":"A giant walrus appears!","size":10,"time":"2014-03-10 19:57:38.562500591 -0400 EDT"} {"animal":"walrus","level":"info","msg":"Tremendously sized cow enters the ocean.","size":9,"time":"2014-03-10 19:57:38.562527896 -0400 EDT"} {"level":"fatal","msg":"The ice breaks!","number":100,"omg":true,"time":"2014-03-10 19:57:38.562543128 -0400 EDT"} With the default logrus.SetFormatter(&logrus.TextFormatter{}) when a TTY is not attached, the output is compatible with the logfmt format: time="2015-03-26T01:27:38-04:00" level=debug msg="Started observing beach" animal=walrus number=8 time="2015-03-26T01:27:38-04:00" level=info msg="A group of walrus emerges from the ocean" animal=walrus size=10 time="2015-03-26T01:27:38-04:00" level=warning msg="The group's number increased tremendously!" number=122 omg=true time="2015-03-26T01:27:38-04:00" level=debug msg="Temperature changes" temperature=-4 time="2015-03-26T01:27:38-04:00" level=panic msg="It's over 9000!" animal=orca size=9009 time="2015-03-26T01:27:38-04:00" level=fatal msg="The ice breaks!" animal=orca err="It's over 9000!" number=100 omg=true size=9009 To ensure this behaviour even if a TTY is attached, set your formatter as follows: logrus.SetFormatter(&logrus.TextFormatter{ DisableColors: true, FullTimestamp: true, }) Logging Method Name If you wish to add the calling method as a field, instruct the logger via: logrus.SetReportCaller(true) This adds the caller as 'method' like so: {"animal":"penguin","level":"fatal","method":"github.com/sirupsen/arcticcreatures.migrate","msg":"a penguin swims by","time":"2014-03-10 19:57:38.562543129 -0400 EDT"} time="2015-03-26T01:27:38-04:00" level=fatal method=github.com/sirupsen/arcticcreatures.migrate msg="a penguin swims by" animal=penguin Note that this does add measurable overhead - the cost will depend on the version of Go, but is between 20 and 40% in recent tests with 1.6 and 1.7. You can validate this in your environment via benchmarks: go test -bench=ReportCaller Case-sensitivity The organization's name was changed to lower-case. If you are getting import conflicts due to case sensitivity, please use the lower-case import: github.com/sirupsen/logrus. Example The simplest way to use Logrus is simply the package-level exported logger: package main import "github.com/sirupsen/logrus" func main() { logrus.WithFields(logrus.Fields{ "animal": "walrus", }).Info("A walrus appears") } Note that it's completely api-compatible with the stdlib logger, so you can replace your log imports everywhere with log "github.com/sirupsen/logrus" and you'll now have the flexibility of Logrus. You can customize it all you want: package main import ( "os" log "github.com/sirupsen/logrus" ) func init() { // Log as JSON instead of the default ASCII formatter. log.SetFormatter(&log.JSONFormatter{}) // Output to stdout instead of the default stderr // Can be any io.Writer, see below for File example log.SetOutput(os.Stdout) // Only log the warning severity or above. log.SetLevel(log.WarnLevel) } func main() { log.WithFields(log.Fields{ "animal": "walrus", "size": 10, }).Info("A group of walrus emerges from the ocean") log.WithFields(log.Fields{ "omg": true, "number": 122, }).Warn("The group's number increased tremendously!") log.WithFields(log.Fields{ "omg": true, "number": 100, }).Fatal("The ice breaks!") // A common pattern is to re-use fields between logging statements by re-using // the logrus.Entry returned from WithFields() contextLogger := log.WithFields(log.Fields{ "common": "this is a common field", "other": "I also should be logged always", }) contextLogger.Info("I'll be logged with common and other field") contextLogger.Info("Me too") } For more advanced usage such as logging to multiple locations from the same application, you can also create an instance of the logrus Logger: package main import ( "os" "github.com/sirupsen/logrus" ) // Create a new instance of the logger. You can have any number of instances. var logger = logrus.New() func main() { // The API for setting attributes is a little different than the package level // exported logger. See Godoc. logger.Out = os.Stdout // You could set this to any `io.Writer` such as a file // file, err := os.OpenFile("logrus.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666) // if err == nil { // logger.Out = file // } else { // logger.Info("Failed to log to file, using default stderr") // } logger.WithFields(logrus.Fields{ "animal": "walrus", "size": 10, }).Info("A group of walrus emerges from the oc