How are Firebase Cloud Functions invocations counted? - node.js

Question

I have plenty of functions in my program with Firebase Cloud Functions. But I'm not sure how the invocations are counted. I am asking this so that I can minimise my invocations as much as possible.
TO start off, I have a function:
export const fucntionOne = functions.auth.user().onCreate((user) => {
console.log('1 invocation used!!')
})
When a new user joins, this function will be executed and ofcourse it will consume my 1 invocation.
So before asking the question here, I did a couple of experiments and found out that if I use another function functionTwo and call it in the first one like this:
export const fucntionOne = functions.auth.user().onCreate((user) => {
console.log('1 invocation used!!')
functionTwo()
})
function functionTwo(){
console.log('Second function worked. . .')
}
This time I was expecting my function invocation count by 2. But it did increased only by 1. This is fine.
But let's say I use a function with some relation with firebase-realtime-database, let's say save or retrieve data using either .onCreate() or .onDelete() and so one and call the function like:
export const fucntionOne = functions.auth.user().onCreate((user) => {
console.log('1 invocation used!!')
})
export const functionOnCreate = functions.database
.ref('/path')
.onCreate((snapshot, context) => {
//Do any thing in the function
console.log(`functionOnCreate executed.`)
return <something>
})
Now let's be clear, functionOnCreate() is executed when some nodes are created using functionOne() in the database using .onCreate() method.
BUT, this time it costed me 2 Invocations.
Okay, I'm clear that it's because functionOnCreate() is being called by [or invoked by] firebase functions so it might be the reason for it.
But if I manage to perform tasks on database by manually calling functions like functionTwo() did. Then will it SAVE me from some extra function invocations?

Answer 1

You are charged for the number of times one of your Cloud Functions is invoked. In your second code snippet, you have only one Cloud Function. Calls inside this Cloud Function to other regular JavaScript functions are not charged operations.
You are charged for the amount of time that your code runs, and for the memory it has allocated during that time. Calling multiple regular functions will increase the time the code runs, and may increase the memory required.
Performing the additional database writes in your functions.auth.user().onCreate triggered Cloud Function will indeed prevent a charge for the functions.database.ref('/path').onCreate( triggered Cloud Function. I recommend that you do some calculations on the number of invocations though, as invocation count is seldom a major factor in their cost.