Distributed locking when cache expires?

[chr4ss12]

nice package! I have gotten a question if this package supports my use case.

My setup:

3 separate webservers running nodeJS.

Currently,

each webserver holds 80mb worth of data, that is refreshed every 10 minutes using setInterval() with a call to a database. One database call can be quite expensive and take long time to compute (roughly a minute), so essentially around 10 minutes I'll have 3 (because of 3 webservers) very expensive / large db calls go off. (For the sake of this question I have simplified it, in reality I've got multiple webservers with 20+ clusters, so there will be a lot of db calls).

I am now investigating how to basically make 1 database call in every 10 minutes and have everyone fetch the cached db data from redis instead.

The part I don't seem to understand is how do I ensure if the redis cache expires, that only 1 webserver is actually going to do an expensive db call & update the value while all the other webservers still use the old data?

Ideally I would like to use something like this (pseudocode):

const getCachedItem = (keyId, fetchFn) => {

   if(localCache[keyId] && !localCache[keyId].stale) return localCache[keyId];

   while(true) {

       // lets see if anything exists in distributed cache
       if(redisCache[keyId]){
          localCache[keyId]=redisCache[keyId]
          return localCache[keyId];
       } 

       // looks like nothing in distributed cache,
       // lets try to acquire the lock and compute the value!

       await tryToAcquireDistributedLockIfItsAvailable(`lock${keyId}`, async () => {
          // We have acquired distributed lock
         // verify if the cache is still empty
         // as there could have been other servers that actually already did the expensive work
         if (redisCache[keyId]){
              localCache[keyId]=redisCache[keyId]
             return localCache[keyId];
         }

          const expensive = await fetchFn();
          redisCache[keyId]=expensive; // items in redis cache expire by themselves after XXX by having TTL.
          localCache[keyId]=expensive;

          return localCache[keyId];
       });

       // Failed to acquire the distributed lock,
       // which can indicate that someone else has the lock and is doing the expensive computation
       // If we have local stale data available, we'll return that
      if (localCache[keyId]) return localCache[keyId];

       // If we have no data at all available
      // We are going to wait a little, and try again to acquire the lock 
      await sleep(200);
  }
}