Our setup was effectively as follows: - AWS Lambda functions being spawned in us-east-1, from a separate AWS sub account. - Connections were all made to the public address provisioned for MySQL protocol access to PlanetScale, using port 3306. The infrastructure did also reside in us-east-1. - Between the Vitess components themselves, and once inside our own network boundaries, we use gRPC to communicate.
Since the goal we set was to hit one million, and realizing we were staying just barely within the limits of the Lambda default quotas, we didn't aggressively try to push beyond that. Some members of our infrastructure team did notice what appeared to be some kind of rate limiting when running the tests multiple times consecutively. Many tests before and after succeeded with no such issues, so we attributed it to a temporary load balancer quirk, but it might be worth going back to confirm if this is the behavior we saw.