Develop Reference

Will Mongo DB Connection closes or expires automatically

I have written a Queue Trigger Azure Function App(Node JS) where on each queue trigger data will be inserted into MongoDB. I am creating MongoClient above function level and re-using same MongoClient for all the Triggers
if(mongoClient.topology.isConnected())
//Use Same Connection
else //Creating new client
mongoClient = await mongoDB.MongoClient.connect();
Sometimes on my mongo db cluster i am getting error connections to your cluster(s) have exceeded i dont understand is it because i am keeping connection open for too long? will connection automatically expire after sometime? Is it good to keep Client Connection above function level and reuse it? Can some one suggest please.
If i do open and close connection at function level then i am getting another error in function Cannot use Session that has ended

If you've deployed the Function App in Consumption Plan, then the number of outbound connections is limited (~600/instance) but you'll get the connections exceeded when you exceed the limit.
I would suggest enabling the Application Insights on the Function App to track the requests time, response time and other metrics that helps to troubleshoot more.
Is it good to keep Client Connection above function level and reuse it?
Yes, you can keep client connections above function level and reuse them instead of creating new connection whatever the client connection it is Http Client, Document Client or Database client.
Do not create a new client with every function invocation.
Do create a single, static client that every function invocation can use.
Consider creating a single, static client in a shared helper class if different functions use the same service.
Refer to MSFT Doc of Azure Functions Client Connections regarding the best practices when managing the client connections in Function Instances.

Issue using Cloud Functions to sync realtime database with Firestore

I'm using an extremely simple Cloud Function to (try to) keep my realtime database in sync with the Firestore.
exports.copyDocument = functions.database.ref('/invoices/{companyId}/{documentId}')
.onWrite((change, context) => {
if (!change.after.exists()) {
return null;
}
return admin.firestore().collection('companies').doc(context.params.companyId).collection('invoices')
.doc(context.params.documentId)
.set(change.after.val());
});
Unfortunately, I am seeing issues where sometimes the Cloud Firestore document does not have the latest copy of the realtime DB data. It's infrequent, but nonetheless impacting my end users.
Why is this happening?
Two ideas I had were -
The Firestore is possibly unavailable to write to in the Cloud Function, and I don't have retries enabled in my Cloud Function, so it could just be erroring out. Enabling retries will solve my problem. However, I have absolutely 0 error logs of this happening.
User makes change A, then user makes change B 2-3 seconds later. In this case, it's possible, I guess, that the Cloud Function trigger for change A hasn't executed, but the trigger for change B quickly executes, then the change A trigger executes and copies 'stale' data. Possible remedies would be to fetch the latest version again from the realtime database in my Cloud Function (not ideal, it's nice using change.after.val()), or perhaps keep some incrementing integer on my document, and instead copy it to the Firestore using a transaction that compares versions instead of a simple set().
The only error message I do see in my Cloud Function error logs is:
The request was aborted because there was no available instance. Additional troubleshooting documentation can be found at: https://cloud.google.com/functions/docs/troubleshooting#scalability
But those docs indicate that this error is always retried, even without explicitly enabling function retries.
I am leaning towards issue 1 - the Firestore just 'blips' sometimes, retries aren't enabled, and I'm not logging the failed promise properly. If this is the case - how can I fix this logging?

Firestore suddenly has a huge trigger delay

We are running an application on Firestore and got a simple trigger that when order's details are created or updated some of it's information should be rewritten in the parent order collection.
The function for this got following code
export const updateOrderDetails = functions
.region(FUNCTION_REGION)
.firestore.document("orders/{orderId}/details/pickupAndDropoff")
.onWrite(async (change, context) => {
return await admin
.firestore()
.collection("orders")
.doc(context.params.orderId)
.set({ pickupAndDropoff: change.after.data() }, { merge: true });
});
It was work fine before, but now at random about every third of its executions is delayed. Sometimes by few minutes. In Cloud Function logs we see normal execution times <200ms, so it seems the trigger runs after a huge pause.
What's worse from time to time our change.after.data() is undefined, but we never delete anything - it's just updates and creates.
It was working fine, we did not changed nothing since last week, but now it started to have this unexpected delays. We've also checked the firebase status, but there are no malfunctions in firebase functions service. What can be the cause of this?

The problem can be due to the monotonically increasing orderId as the parameter passed here:
...
.collection("orders")
.doc(context.params.orderId)
...
If you can check once if the orderId passed here is monotonically increasing with each request? It can lead to hotspots which impacts latency.
To explain, I think the write rate must be changing at different day's and time's - as the user traffic using the application or load testing requests changes - which is creating the unexpected kind of behaviour. At low write rate, the requests are working as expected most of the time. At high write rate, the requests are facing hotspot situation in the firestore as mentioned in the firestore documentation resulting in delays (latency issue).
Here is the relevant link to firestore best practices documentation.

Thanks to Frank van Puffelen suggestion we've sent this question directly to Firebase support and after their internal investigation we've got the reply from an engineering team that it was in fact an infrastructure malfunction.
The reply I got from them was:
I escalated the issue to recover more information. So far it appears that there was an issue with pub/sub delivering and creating the event. The Firestore team is also communicating with the pub/sub team to investigate the issue and prevent future incidents.
It seems that the best way to deal with such problems is to quickly write directly to Firebase support team, because as they mentioned in the automatic reply I got after sending a support ticket:
For Firebase outages not listed on the status dashboard, we'll respond within 4 hours.
which seems to be the best option.

Can't change data in Firebase Realtime Database when using Cloud Functions

I want to reset a specific value in my Firebase Realtime Database every day at 12:00 AM. I'm using Firebase Cloud Functions to do this. This is the code that I have:
exports.dailyReset = functions.pubsub.schedule('0 0 * * *').onRun((context) => {
exports.resetValue = functions.database.ref('/users/{userId}')
.onWrite((change, context) => {
var ref = change.data.ref;
ref.update({
"daily": 0
});
return ref.update({"daily": 0});
});
return null;
});
Upon testing the script, it doesn't work. It's not resetting the value in my Firebase Realtime Database. Can someone tell me how do I fix this?

It's not possible to use the Functions SDK to write to the database. functions can only be used to establish triggers that run when the triggering event occurs.
In other words, functions.database.ref('/users/{userId}').onWrite() isn't going to write anything at all.
If you want to write to Realtime Database from a nodejs program, you should use the Firebase Admin SDK to write data.

The Cloud Functions triggers in your index.js file have to be known and fixed when run firebase deploy. That means you can't dynamically create triggers from inside a Cloud Functions, as you're trying to do.
The common approaches for dynamic scheduling are:
Have a single Cloud Function that runs periodically and then executes the tasks for the past time period.
Dynamically schedule Cloud Functions with Cloud Tasks, as Doug describes in his blog post How to schedule a Cloud Function to run in the future with Cloud Tasks (to build a Firestore document TTL).
But in your case, why do you even need the onWrite trigger? Can't you just import the Admin SDK, user that to read all users, and then delete them?

Best way to have a Node.JS server keep updated with a FireBase database in real time?

I currently have a Node.JS server set up that is able to read and write data from a FireBase database when a request is made from a user.
I would like to implement time based events that result in an action being performed at a certain date or time. The key thing here though, is that I want to have the freedom to do this in seconds (for example, write a message to console after 30 seconds have passed, or on Friday the 13th at 11:30am).
A way to do this would be to store the date/time an action needs be performed in the database, and read from the database every second and compare the current date/time with events stored so we know if an action needs to be performed at this moment. As you can imagine though, this would be a lot of unnecessary calls to the database and really feels like a poor way to implement this system.
Is there a way I can stay synced with the database without having to call every second? Perhaps I could then store a version of the events table locally and update this when a change is made to the database? Would that be a better idea? Is there another solution I am missing?
Any advice would be greatly appreciated, thanks!
EDIT:
How I currently initialise the database:
firebase.initializeApp(firebaseConfig);
var database = firebase.database();
How I then get data from the database:
await database.ref('/').once('value', function(snapshot){
snapshot.forEach(function(childSnapshot){
if(childSnapshot.key === userName){
userPreferences = childSnapshot.val().UserPreferences;
}
})
});

The Firebase once() API reads the data from the database once, and then stops observing it.
If you instead us the on() API, it will continue observing the database after getting the initial value - and call your code whenever the database changes.

It sounds like you're looking to develop an application for scheduling. If that's the case you should check out node-schedule.
Node Schedule is a flexible cron-like and not-cron-like job scheduler
for Node.js. It allows you to schedule jobs (arbitrary functions) for
execution at specific dates, with optional recurrence rules. It only
uses a single timer at any given time (rather than reevaluating
upcoming jobs every second/minute).
You then can use the database to keep a "state" of the application so on start-up of the application you read all the upcoming jobs that will be expected and load them into node-schedule and let node-schedule do the rest.

The Google Cloud solution for scheduling a single item of future work is Cloud Tasks. Firebase is part of Google Cloud, so this is the most natural product to use. You can use this to avoid polling the database by simply specifying exactly when some Cloud Function should run to do the work you want.
I've written a blog post that demonstrates how to set up a Cloud Task to call a Cloud Functions to delete a document in Firestore with an exact TTL.