I'm building in a CRON like module into my service (using node-schedule) that will get required into each instance of my multi-core setup and I'm wondering since they are all running their own threads and they are all scheduled to run at the same time, will they get called for every single thread or just once because they're all loading the same module.
If they do get called multiple times, then what is the best way to make sure the desired actions only get called once?
The best way to handle this in a generic way is to have a shared database that you write a "lock" entry to. As in, let's say all tasks wrote a DB entry such as {instanceId: "a", taskId: "myTask", timestamp: "2021-12-22:10:35"}.
All tasks would submit the same thing except with their own instanceId. You then have an unique index on 'timestamp' so that only 1 gets accepted.
Then they all do a query and see if their node was the one that was accepted to do the cron.
You could do the same thing but also add a "random" field that generates a random number and the task with the lowest number wins.