zlg (zerolog-gcp)

zlg is a (hopefully) straightforward LevelWriter for using zerolog with Google Cloud Operations Logging, which used to be named Stackdriver.

Some notable features:

• The first log written to Cloud Logging is a slow, blocking write to confirm connectivity + permissions, but all subsequent writes are non-blocking.
• Flushes all logs before a .Fatal() or .Panic()
• Ensure that all zlg-created loggers are flushed before program exit with defer zlg.Flush()
• Overridable Cloud Monitoring levels (zerolog -> Cloud Logging):
  • Trace -> Default
  • Warn -> Warning
  • Cloud Logging's Alert and Emergency levels are not used.

Getting Started

The usual cases

Logging only to Stackdriver:

import zlg "github.com/mark-ignacio/zerolog-gcp"

// [...]

gcpWriter, err := zlg.NewCloudLoggingWriter(ctx, projectID, logID, zlg.CloudLoggingOptions{})
if err != nil {
    log.Panic().Err(err).Msg("could not create a CloudLoggingWriter")
}
log.Logger = log.Output(gcpWriter)

For non-GCP-hosted situations, you can log to both stdout/stderr and GCP without much additional fuss.

gcpWriter, err := zlg.NewCloudLoggingWriter(ctx, projectID, logID, zlg.CloudLoggingOptions{})
if err != nil {
    log.Panic().Err(err).Msg("could not create a CloudLoggingWriter")
}
log.Logger = log.Output(zerolog.MultiLevelWriter(
    zerolog.NewConsoleWriter(),
    gcpWriter,
))

To ensure that the last asynchronous logs are delivered to Cloud Logging, zlg keeps a reference to all logging.Logger structs that zlg itself creates. If memory leaks of loggers are a concern, consider specifying providing a logger client via zlg.CloudLoggingOptions instead.

gcpWriter, err := zlg.NewCloudLoggingWriter(ctx, projectID, logID, zlg.CloudLoggingOptions{})
if err != nil {
    log.Panic().Err(err).Msg("could not create a CloudLoggingWriter")
}
defer zlg.Flush()
doEverythingElse()

More advanced usage involves a non-empty zlg.CloudLoggingOptions, which allows for log level and GCP client customization.