libkv

libkv provides a Go native library to store metadata.

The goal of libkv is to abstract common store operations for multiple Key/Value backends and offer the same experience no matter which one of the backend you want to use.

For example, you can use it to store your metadata or for service discovery to register machines and endpoints inside your cluster.

You can also easily implement a generic Leader Election on top of it (see the swarm/leadership package).

As of now, libkv offers support for Consul, Etcd and Zookeeper.

Example of usage

Create a new store and use Put/Get

package main

import (
	"fmt"
	"time"
	
	"github.com/docker/libkv"
	"github.com/docker/libkv/store"
	log "github.com/Sirupsen/logrus"
)

func main() {
	client := "localhost:8500"

	// Initialize a new store with consul
	kv, err := libkv.NewStore(
		store.CONSUL, // or "consul"
		[]string{client},
		&store.Config{
			ConnectionTimeout: 10*time.Second,
		},
	)
	if err != nil {
		log.Fatal("Cannot create store consul")
	}

	key := "foo"
	err = kv.Put(key, []byte("bar"), nil)
	if err != nil {
		log.Error("Error trying to put value at key `", key, "`")
	}

	pair, err := kv.Get(key)
	if err != nil {
		log.Error("Error trying accessing value at key `", key, "`")
	}

	log.Info("value: ", string(pair.Value))
}

You can find other usage examples for libkv under the docker/swarm or docker/libnetwork repositories.

Warning

There are a few consistency issues with etcd, on the notion of directory and key. If you want to use the three KV backends in an interchangeable way, you should only put data on leaves (see Issue 20 for more details). This will be fixed when etcd API v3 will be made available (API v3 drops the directory/key distinction). An official release for libkv with a tag is likely to come after this issue being marked as solved.

Other than that, you should expect the same experience for basic operations like Get/Put, etc.

Calls like WatchTree may return different events (or number of events) depending on the backend (for now, Etcd and Consul will likely return more events than Zookeeper that you should triage properly). Although you should be able to use it successfully to watch on events in an interchangeable way (see the swarm/leadership or swarm/discovery packages in docker/swarm).

Create a new storage backend

A new storage backend should include those calls:

type Store interface {
	Put(key string, value []byte, options *WriteOptions) error
	Get(key string) (*KVPair, error)
	Delete(key string) error
	Exists(key string) (bool, error)
	Watch(key string, stopCh <-chan struct{}) (<-chan *KVPair, error)
	WatchTree(directory string, stopCh <-chan struct{}) (<-chan []*KVPair, error)
	NewLock(key string, options *LockOptions) (Locker, error)
	List(directory string) ([]*KVPair, error)
	DeleteTree(directory string) error
	AtomicPut(key string, value []byte, previous *KVPair, options *WriteOptions) (bool, *KVPair, error)
	AtomicDelete(key string, previous *KVPair) (bool, error)
	Close()
}

You can get inspiration from existing backends to create a new one. This interface could be subject to changes to improve the experience of using the library and contributing to a new backend.

##Roadmap

• Make the API nicer to use (using options)
• Provide more options (consistency for example)
• Improve performance (remove extras Get/List operations)
• Add more exhaustive tests
• New backends?

##Contributing

Want to hack on libkv? Docker's contributions guidelines apply.

##Copyright and license

Code and documentation copyright 2015 Docker, inc. Code released under the Apache 2.0 license. Docs released under Creative commons.