Share gcp external load balancer across multiple projects

Load balancers using serverless NEG backends must be created in the same project as the Cloud Run (fully managed), App Engine, or Cloud Functions services pointed to by the NEG.

You can use Internet NEG to overcome this as its purpose is to route the requests from the global HTTPs Load Balancer to an internet endpoint, defined by its IP or its fully qualified domain name across different projects.

So, Instead of calling internally an App Engine service with a serverless NEG, we can use an Internet NEG to call it externally.

Please refer to the below public document created by a googler on how to create the same(Cloud Run) https://medium.com/google-cloud/cloud-run-and-load-balancing-go-beyond-your-own-project-adfa1c8b001d

Please refer this for public doc on creating the external HTTP(S) load balancer https://cloud.google.com/load-balancing/docs/https/setting-up-https-serverless