logger

Common logger library for golang projects

import "github.com/relex/gotils/logger"

logger.Info("hey there!")
logger.Fatal("Oh my god!")
...
logger.WithField("file", "log.txt").Errorf("failed to open: %v", err)
...
subLogger := logger.WithFields(map[string]interface{}{
	"key2": "val2",
	"key3": "val3",
})
subLogger.Warn("something broke")
...
logger.Exit(0) // must exit the program via .Exit to flush logs properly

Log levels:

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

The default level is Info. To change:

export LOG_LEVEL="debug"   # case-insensitive

or

logger.SetLogLevel(logger.DebugLevel)

PS: trace-level logs are never forwarded to upstream regardless of the log level set.

Fatal and Panic

• logger.Fatal ends the program with exit code 1 after logging. It uses logger.Exit and waits at least 3 seconds for log forwarding connection to flush if set up by SetUpstreamEndpoint.
• logger.Panic calls panic after logging. It only waits 1 second for log forwarding connection to flush.

Log format

By default logger is using the TextFormat, which is like:

time="2006/02/01T15:04:05.123+0200" level=debug msg="Started observing beach"

But you can select a JSON format with SetFormat function.

logger.SetJSONFormat()

Then, the log, will be like:

{"timestamp":"2006/02/01T15:04:05.123+0200","level":"info","message":"A group of walrus emerges from the ocean"}

Log output

By default all logs are going to stderr, but you can set it to go into file:

err := logger.SetOutputFile("/tmp/my_app.log")
if err != nil {
    // handle
}

Log forwarding

Forwarding to upstream for log collection can be enabled by:

logger.SetUpstreamEndpoint("127.0.0.1:10501")

The upstream address needs to be an address to Datadog agent's TCP input.

Only TCP protocol is supported and the format of logs to upstream is always JSON, regardless of the main format used by logger(s).

Error recovery

There are two implementations for log forwarding to upstream: buffered for remote endpoint and unbuffered for local endpoint. It's chosen automatically by the type of endpoint host.

The buffered implementation queues all logs in GO channel and flush it every 1/10 second; It deals with network errors and attempts reconnection or resending indefinitely until logger.Exit is called (when it would retry one more time to flush all remaining logs).

The unbuffered one ignores any logs failed to send, as error recovery would block logging functions for too long. However, it attempts to reconnect for every new log if the previous one fails.

Both print internal errors to stderr.