jrhouston / k8slock

A distributed locking module for Go using the Lease resource from the Kubernetes coordination API

k8slock

k8slock is a Go module that makes it easy to do distributed locking using the Lease resource from the Kubernetes coordination API.

If you want to use Kubernetes to create a simple distributed lock, this module is for you.

This module implements the sync.Locker interface using the Lock() and Unlock() functions.

This module also supports using contexts via the LockContext() and UnlockContext() functions.

Basic Usage

package main

import "github.com/jrhouston/k8slock"

func main() {
    locker, err := k8slock.NewLocker("example-lock")
    if err != nil {
        panic(err)
    }

    locker.Lock()
    // do some work
    locker.Unlock()
}

Basic Usage – Context

package main

import (
    "context"
    "github.com/jrhouston/k8slock"
)

func main() {
    locker, err := k8slock.NewLocker("example-lock")
    if err != nil {
        panic(err)
    }

    ctx := context.Background()
    if err := locker.LockContext(ctx); err != nil {
        fmt.Println("Error trying to lock", err)
    }

    // do some work
    
    if err := locker.UnlockContext(ctx); err != nil {
        fmt.Println("Error trying to unlock", err)
    }
}

Locker Options

The locker can be configured using the following functional options:

Option	Details
TTL(duration)	The duration until the lock expires and can be forcibly claimed. By default the lock can be held infinitely.
RetryWaitDuration(duration)	The duration to wait before retrying after failing to acquired the lock. Default: 1 second.
InClusterConfig()	Get the kubernetes client config from inside a pod. Defaults to a clientset using the local kubeconfig.
Clientset(kubernetes.Interface)	Configure a custom Kubernetes Clientset. Defaults to a clientset using the local kubeconfig.
Namespace(string)	The kubernetes namespace to store the Lease resource. Defaults to "default".
ClientID(string)	A unique ID for the client that is trying to obtain the lock. Defaults to a random UUID.
CreateLease(bool)	Create a Lease resource if it does not already exist. Defaults to true.

e.g:

locker, err := k8slock.NewLocker("example-lock", k8slock.Namespace("locks"), k8slock.ClientID("client-0"))

k8slock's Issues

Add non-blocking support

This package implements the sync.Locker interface, which blocks until the Lock is acquired. Some clients might prefer a non-blocking interface so they can control the strategy used to retry acquiring the lock.

Copy and paste error in `lock()`?

k8slock/locker.go

Lines 187 to 192 in 6f294b1

	lease.Spec.HolderIdentity = pointer.String(l.clientID)
	if lease.Spec.LeaseTransitions != nil {
	lease.Spec.LeaseTransitions = pointer.Int32((*lease.Spec.LeaseTransitions) + 1)
	} else {
	lease.Spec.LeaseTransitions = pointer.Int32((*lease.Spec.LeaseTransitions) + 1)
	}

Here, the code checks if lease.Spec.LeaseTransitions is nil but the if-else branches are identical.

pointer.Int32((*lease.Spec.LeaseTransitions) + 1)

will segfault with a nil lease.Spec.LeaseTransitions

Add Renew() function

Function to extend the lock via the timeRenewed field.

I see a lot of panic()

First I thought: Great, a nice library which helps me to sync two controllers.

Then I looked at the code and see many panic() calls.

Just out of curiosity, why do you use panic() so often?