Firebase Cloud Function Push Notification Really Slow - ios

Question

I have an iOS app that sends a time sensitive push notification from an event via Cloud Firestore-triggered function.
In my function, I do a simple get operation prior to sending out the push notification, and it gets delivered from 30 sec up to 1 min. Can anyone advise on improving the speed?
I've looked at the online documentation talking about setting a minimum # of instances to reduce a cold start. I've also looked at this SO answer. As someone that's new to this, I admittedly am having difficulty following and pinpointing my advised next step. Any help and guidance would be extremely appreciated.
exports.pushNotification = functions.firestore.document('/users/{userId}').onUpdate((change, context) => {
var recipientUid = context.params.userId;
return admin.firestore().collection('users').doc(recipientUid).get().then(doc => {
const userData = doc.data();
var fcmToken = userData.fcmToken;
var message = {
notification: {
title: sendingTitle,
body: sendingMessage
},
apns : {
payload : {
aps : {
badge : 1,
sound: "default"
}
}
},
token: fcmToken
};
admin.messaging().send(message)
.then((response) => {
console.log('Successfully sent push notification message:', response);
return;
})
.catch((error) => {
console.log('Error sending message:', error);
return;
});
})
});

Answer 1

One possible cause is that you don't correctly manage the life cycle of your Cloud Function: as a matter of fact you are not returning the Promises chain, as shown below (see the comments in the code):
exports.pushNotification = functions.firestore.document('/users/{userId}').onUpdate((change, context) => {
var recipientUid = context.params.userId;
return admin.firestore().collection('users').doc(recipientUid).get()
.then(doc => {
const userData = doc.data();
var fcmToken = userData.fcmToken;
var message = { ... };
return admin.messaging().send(message) // !!! See the return here
}) // And see also that we close the then block here
.then((response) => {
console.log('Successfully sent push notification message:', response);
return;
})
.catch((error) => {
console.log('Error sending message:', error);
return;
});
});
For more details on how to correctly manage the life cycle, I would suggest you watch the 3 videos about "JavaScript Promises" from the Firebase video series as well as read the following doc. Also, reading the doc on how to chain Promises will help.