How to unlock a Lock you only have the resource name? about node-redlock HOT 3 CLOSED

Hi @dvergeylen – So sorry for the slow reply here!

So, the library expects an actual instance of Lock for two reasons.

1. The method is actually supposed to mutate its expiration to immediately invalidate it. This prevents accidentally extending a lock you are attempting to invalidate.
2. More importantly, the lock value is what prevents a dangerous race condition. Imagine you have 2 servers, and server A gets a lock on SOME_RESOURCE. Eventually, server A is done with the resource, and sends a request to redis to release the lock on SOME_RESOURCE. Now, due to the asynchronous nature of network requests, it's possible that the lock expires before the request reaches and is processed by redis. It's also possible that in that time, server B is able to successfully acquire a NEW lock on SOME_RESOURCE. If only the resource name is used in the eventually-processed "unlock" request, then it would be possible for it to prematurely release the new lock acquired by server B! To prevent this, each lock has a cryptographically random value, to make it unique. This way, the "unlock" request from server A will only succeed if the currently-held lock is the one it's attempting to release.

All that to say, you'll almost certainly want to track at least the lock's resource and value, if you aren't able to keep a reference to the original lock.

To unlock the resource, the "most correct" way would be:

const Redlock = require('redlock');

const savedLockResource = 'SOME RESOURCE';
const savedLockValue = 'xxxxxx';

lock = new Redlock.Lock(redlock, savedLockResource, savedLockValue, 1);
lock.unlock();

More concisely, you could get away with:

redlock.unlock({ resource: 'SOME_RESOURCE', value: 'xxxxxx' });

Hope that helps!

from node-redlock.

I could find a workaround 😸. But I am still interested if you have an elegant way to retrieve a lock from its resource name.

from node-redlock.

Hope that helps!

It does! Thank you @mike-marcacci ! 👍

from node-redlock.