Run a cron job only once after a set time - firebase

Question

I need to run a cron job to perform a specific cloud function after a set interval only once but a bit unsure of how to do it. Is there any way to do this through the current google cloud platform?

Answer 1

Update following our discussion below through comments:
If you want to "change a document in your Firestore database 2 hours after it has been created" you could do as follows:
When creating the document in Firestore, save the date/time of creation, e.g. with firebase.firestore.FieldValue.serverTimestamp()
Have an HTTP Cloud Function that you call regularly as explained below (every minutes? every 5 minutes?) and that, first, selects the documents that were created 2 hours ago (based on the saved timestamp) and then do the desired action on these docs.
If you want to trigger a Cloud Function through a cron job, note that you would normally do that through an HTTP Cloud Function, calling the Cloud Function URL via the cron job.
You can either use an external service like cron-job.org or you can use GCP's App Engine and Cloud Pub/Sub
See this video: https://www.youtube.com/watch?v=fEBPAMSk5_8
and this Blog post: https://firebase.googleblog.com/2017/03/how-to-schedule-cron-jobs-with-cloud.html
both from the Firebase team.
Finally note that recently GCP launched a new product, Cloud Scheduler, which can be used to call HTTP Cloud Functions.

Answer 2

Sorry for late answer. Once upon time, I am stuck with this issue too. You sure can schedule a job executed once at particular time. But, you must use multiple platform as Firebase Cloud Function has time limit to cron task. If you look at Quotas and limits document for Time Limit of Firebase, you can see that Firebase cloud functions have set time limits until they are canceled (540 seconds or 9 minutes). So you can't cron a job executed after more than 9 minute with cloud function. But you can use Heroku server to cron a job without paying. Unfortunately, Heroku apps sleep after 30 minutes if there is no task along the time interval. However, you can keep awake with external server such as cron-job.org. You can get unlimitedly your app awake by applying pinging to your Heroku app every minute less than 30 minutes. You can use node-schedule to cron a job executed once for all time by using this code there:
const schedule = require('node-schedule');
const date = new Date(2012, 11, 21, 5, 30, 0);
const job = schedule.scheduleJob(date, function(){
console.log('The world is going to end today.');
});
You can get current time or timestamp for Firestore and add time interval to current date to schedule as you desire. Dont forget to use timezone for it. You can use rule to set timezone like that:
const rule = new schedule.RecurrenceRule();
rule.dayOfWeek = [0, new schedule.Range(0, 6)]; //all days
rule.hour = req.body.hour;
rule.minute = req.body.minute;
rule.second = req.body.second;
rule.tz = "Europe/Istanbul"; // You can specify a timezone!
Here, you can get request from client side by fetching time specification from user. And use schedule job module for one time task like that:
const job = schedule.scheduleJob(rule, function(data) {
console.log("Job ran #", new Date().toString());
}.bind(null, dataFuture));
Here you can use user data with .bind() by entering variable just like dataFuture variable. If your users use native android platform, you can specify time interval by entering hour_of_day and minute as:
Date currentTime = Calendar.getInstance().getTime();
Locale aLocale = Locale.forLanguageTag("tr-TR");
Calendar calendar = Calendar.getInstance(aLocale);
calendar.setTime(currentTime);
calendar.add(Calendar.MINUTE, 1);
calendar.add(Calendar.HOUR_OF_DAY, 4);
Alternatively you can use Cloud Task platform. But it may be a bit hard to use.