A dead simple distributed locking library for Node.js and etcd (via node-etcd)
Etcd is a distributed key-value store, built by the CoreOS team, that provides strong guarantees around consistency and partition tolerance. Data is duplicated to all nodes in a given cluster and remains consistent between node failures. Cluster leaders are elected via the Raft consensus algorithm. Etcd provides operations for atomic value swapping/removal based on criteria and TTL for values, making it a perfect media for distributed locks.
A distributed lock is a mechanism that provides serialized flow control on a context that is acted on by more than one process. These processes typically operate on different machines via Service Oriented Architecture. Each process uses an object called a distributed lock to "lock" access to the shared context, aliased by a key, so that only one process, each aliased by a node id, can act on it at a time, thereby ensuring consistency and preventing race conditions.
Redis is great for a lot of things. Caching, keeping processes stateless, and fast access to simply structured data are all cases where Redis shines. However, implementing a distributed lock with Redis via Redlock has several caveats that are unsuitable for many cases. Namely, if you need strong guarantees that a lock will not be acquired by multiple nodes at once even in the event of failure, Redlock isn't a viable option.
Microlock is currently compatible with Etd 2.2.x. Work on support for Etcd 2.2.x - 3.x is in progress.
Requires NodeJS >= 4.0
$ npm install microlockvar os = require('os');
var Etcd = require('node-etcd');
var Microlock = require('microlock');
var key = 'foo'; //name of the lock
var id = os.hostname(); //id of *this* node
var ttl = 5; //5 second lease on lock
var etcd = new Etcd();
var foo = new Microlock.default(etcd, key, id, ttl);
foo.lock().then(function () {
// foo is locked by this node
// do some stuff...
// release the lock
return foo.unlock();
}, function (e) {
if (e instanceof Microlock.AlreadyLockedError) {
// foo is already locked by a different node
}
});import { hostname } from 'os';
import Etcd from 'node-etcd';
import Microlock, { AlreadyLockedError } from 'microlock';
const key = 'foo'; //name of the lock
const id = hostname(); //id of *this* node
const ttl = 5; //5 second lease on lock
const etcd = new Etcd();
const foo = new Microlock(etcd, key, id, ttl);
foo.lock().then(() => {
// foo is locked by this node
// do some stuff...
// release the lock
return foo.unlock();
}, (e) => {
if (e instanceof AlreadyLockedError) {
// foo is already locked by a different node
}
});import { hostname } from 'os';
import Etcd from 'node-etcd';
import Microlock, { AlreadyLockedError } from 'microlock';
async function main () {
const key = 'foo'; //name of the lock
const id = hostname(); //id of *this* node
const ttl = 5; //5 second lease on lock
const etcd = new Etcd();
const foo = new Microlock(etcd, key, id, ttl);
try {
await foo.lock();
// foo is locked by this node
// do some stuff...
// release the lock
await foo.unlock();
} catch (e) {
if (e instanceof AlreadyLockedError) {
// foo is already locked by a different node
}
}
}
main();All methods (except destroy) return promises, making it easy to use features like async/await with ES2016/ES2017 via Babel.
Creates a microlock client for a lock key.
var Etcd = require('node-etcd');
var Microlock = require('microlock');
var etcd = new Etcd();
var foo = new Microlock.default(microlock, 'foo', 'bar');Attempts to lock the key for the node_id.
foo.lock().then(function () {
// foo is locked by this node
}, function (e) {
if (e instanceof Microlock.AlreadyLockedError) {
// foo is already locked by a different node
}
});Attempts to release the key for the node_id.
foo.unlock().then(function () {
// foo is unlocked
}, function (e) {
if (e instanceof Microlock.LockNotOwnedError) {
// foo is not locked by `node_id`
}
})Attempts to renew the lock on key for the node_id.
foo.renew().then(function () {
// foo lease is renewed... ttl is refreshed
}, function (e) {
if (e instanceof Microlock.LockNotOwnedError) {
// foo is not locked by `node_id`
}
})Unbinds listeners/watchers from this client
Emits when the key is unlocked (node agnostic)
foo.on(Microlock.events.unlocked, function () {
//handle unlocked with constant
});
foo.on('unlocked', function () {
//handle unlocked with string
});Emits when the key is locked (node agnostic)
foo.on(Microlock.events.locked, function () {
//handle locked with constant
});
foo.on('locked', function () {
//handle locked with string
}); $ make install $ make $ make lint $ make unitDocker Compose is required
$ make integration etcd_image_version=v2.2.2You can use whatever version you'd like to test against in the command above.
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