How can I initialize firebase app in a serverless model? What is the concurrent app limit? - firebase

Question

I created a serverless function that performs that Firebase Token Validation.
Everything works as intended. Except, I have I get errors on subsequent calls to initialize my app that the default app already exists (same container). This raises some questions.
If my serverless infrastructure was to spin up multiple concurrent containers, each working to initialize the app. Would this also cause this error? That the app is initiailized elsewhere? Or is this error isolated to local instances?
If its the latter, If I provide a named app based on the container it is spun up in, is there a firebase limit to the maximum number of apps that can be initialized at once?
This is how I am initializing the app now:
cred = credentials.Certificate(SERVICE)
firebase_admin.initialize_app(cred)
I could do this but am not sure about firebase app limits or concurrent initializations (cant find any specifics in docs):
cred = credentials.Certificate(SERVICE)
firebase_admin.initialize_app(cred, 'APP-NAME-[CONTAINERID]')
Or, should I just re-write this using my own JWT Decoder and grabbing the public keys from google?
And here is the full error:
Error occurred setting firebase credentials: The default Firebase app already exists. This means you called initialize_app() more than once without providing an app name as the second argument. In most cases you only need to call initialize_app() once. But if you do want to initialize multiple apps, pass a second argument to initialize_app() to give each app a unique name.
UPDATE: AWS Lambda, Python.
I am going to test out with the following, to prevent re-initializing the app within the same container on warm function executions and move forward with the assumption that there are no API limits on performing auth.validate_id_token() and that this won't conflict with concurrent container executions. Ill report back if it tests out differently.
try:
firebase_admin.get_app()
logger.info('firebase already intialized.')
except ValueError as e:
logger.info('firebase not initialized. initialize.')
cred = credentials.Certificate(SERVICE)
firebase_admin.initialize_app(cred)
I will probably still migrate to another JWT validation to reduce function size (since I already have a jwt library for my own app use) and migrate away from relying on Firebase API to decode it.

Answer 1

If you get an error when initializing the admin SDK that says the default app already exists, that just means you're trying to init the admin SDK twice in the same process. Obviously, don't do that. If you init once and only once per process, you will never see this error.
You will have to take some care to only call the init method once per server instance. It's not clear exactly what you're doing from the code you've shown. I don't know about python, but with node, you can init once in a global context without problems. If you need to init during a function execution, you should have some flag to check that ensures the default Firebase app hasn't already been initialized, and init only conditionally based on that flag.