What is the rate limit for GCE instance metadata service?

问题

On a GCP compute environment, I need to get an id_token (expires every 3600s) to make service-to-service authentication (using GCF, Cloud Run etc).

I get this id_token from the instance metadata service:

http://metadata/computeMetadata/v1/instance/service-accounts/default/identity?audience=[...]

Instead of implementing some form of caching+TTL for this identity token, I'm curious if I can call this endpoint every time I will make an outbound RPC (I might make a lot).

That's why I'm curious:

1. What's the rate limit for the instance metadata service?

2. Does the rate limit differ between GCE vs serverless platforms (GAE, GCF, Cloud Run)?

来源：https://stackoverflow.com/questions/58495465/what-is-the-rate-limit-for-gce-instance-metadata-service