slog

README

xk6-slog

This is a k6 extension using the xk6 system.

❗ This is a sort of hack to bypass the builtin logger of k6 because I was too lazy to figure that out. USE AT YOUR OWN RISK!

Example

You can replace console.log() for slog.log() and you'll be able to use structured logs.

NB: UNTESTED with Loki and K6 Cloud. Might not work since this is bypassing Logrus.

Supports the environment variable K6_LOG_FORMAT.

// script.js
import exec from 'k6/execution';
import slog from 'k6/x/slog';

export const options = {
  vus: 1,
  duration: '1s',
  tags: {
    testid: 12345,
  },
};

export default function() {
  slog.setPersistentField("testid", exec.test.options.tags.testid);

  let complexObject = {
    a: {
      b: "c"
    }
  }
  slog.info("this is an info log", "object", complexObject)
}

Build

To build a k6 binary with this extension, first ensure you have the prerequisites:

• Go toolchain
• Git

Then:

1. Install xk6:

$ go install go.k6.io/xk6/cmd/xk6@latest

1. Build the binary:

$ xk6 build --with github.com/flinkstech/xk6-slog@latest

Result output:

$ K6_LOG_FORMAT=json ./k6 run script.js

          /\      |‾‾| /‾‾/   /‾‾/   
     /\  /  \     |  |/  /   /  /    
    /  \/    \    |     (   /   ‾‾\  
   /          \   |  |\  \ |  (‾)  | 
  / __________ \  |__| \__\ \_____/ .io

     execution: local
        script: script.js
        output: -

     scenarios: (100.00%) 1 scenario, 2 max VUs, 31s max duration (incl. graceful stop):
              * default: 2 looping VUs for 1s (gracefulStop: 30s)

{"time":"2024-05-15T14:20:19.912684-04:00","level":"INFO","msg":"reponse from test.k6.io","testid":"12345","response":{"url":"https://test.k6.io/"}}
{"time":"2024-05-15T14:20:19.912684-04:00","level":"INFO","msg":"reponse from test.k6.io","testid":"12345","response":{"url":"https://test.k6.io/"}}
{"time":"2024-05-15T14:20:19.954419-04:00","level":"INFO","msg":"reponse from test.k6.io","testid":"12345","response":{"url":"https://test.k6.io/"}}

Possible improvements

I couldn't figure it out with the time I had, but it would be nice to be able to call SetPersistentField() in the setup() stage function.

However, what I noticed is that the logger between setup() and the default function() are not shared.

This would avoid SetPersistentField() being called for every VU/iteration.

I quickly mesured with and without it

# With SetPersistentField() in default function()
avg=1.78ms min=3.66µs med=14.7µs max=63.63ms p(90)=6.21ms p(95)=8.35ms

# Without
avg=1.61ms min=2.62µs med=9.66µs max=62.37ms p(90)=5.97ms p(95)=8.3ms

Documentation

Index

• type Slog
  • func (s *Slog) Debug(msg string, args ...any)
  • func (s *Slog) Error(msg string, args ...any)
  • func (s *Slog) Info(msg string, args ...any)
  • func (s *Slog) Log(msg string, args ...any)
  • func (s *Slog) SetPersistentField(fieldName string, value string)
  • func (s *Slog) Warn(msg string, args ...any)

Types

type Slog

type Slog struct {
	// contains filtered or unexported fields
}

func (*Slog) Debug

func (s *Slog) Debug(msg string, args ...any)

Debug creates a debug log

func (*Slog) Error

func (s *Slog) Error(msg string, args ...any)

Error creates an error log

func (*Slog) Info

func (s *Slog) Info(msg string, args ...any)

Info creates an info log

func (*Slog) Log

func (s *Slog) Log(msg string, args ...any)

Log creates an info log

func (*Slog) SetPersistentField

func (s *Slog) SetPersistentField(fieldName string, value string)

SetPersistentField adds a field to the logs that stay for all the logs Useful to add test run id or tagging metadata

func (*Slog) Warn

func (s *Slog) Warn(msg string, args ...any)

Warn creates a warn log