Drop the `.env`, it's cleaner (ADK should pick up project and location from GCP metadata server)

[steren]

Problem

When deploying ADK to Google Cloud, I must pass a .env file with these:

GOOGLE_GENAI_USE_VERTEXAI=TRUE
GOOGLE_CLOUD_PROJECT=my-project
GOOGLE_CLOUD_LOCATION=us-central1

Proposal

This should not be needed when deploying to GCP:

• GOOGLE_GENAI_USE_VERTEXAI should be assumed to be TRUE unless an API key is provided.
• GOOGLE_CLOUD_PROJECT and GOOGLE_CLOUD_LOCATION should be retrieved from the instance metadata server.

A note on instance metadata server:

Every GCP runtime exposes the same instance metadata server which allows retrieving project and location. See reference for Cloud Run. It's trivial for ADK to query it (see example Go code)

[justingrayston]

1. Doesn't this assume that your agent running on Google Cloud is going to call Gemini in the same region which may not be the case
2. You might be running multiple agent backends loadbalanced, so you may hit different CR regions based on where you are, but still call 1 vertex endpoint for Gemini

I do agree we could have these as good standard defaults when running on Google cloud as long as we allow for override.

[steren]

yes to be clear, I am only suggesting using this as a default behavior, the developer should still be able to customize project / location using .env

[klateefa]

@steren Thank you for reporting this. I understand the request is currently under review. Please keep me posted if anything else is needed. Thanks for your patience.

[a2105z]

Hi — I'd like to take this one on.

I'll add opt-in GCP metadata-server defaults for project/location (and Vertex usage) so Agent Engine / Cloud deploys don't require a .env for those values, while keeping explicit env/CLI overrides. Opening a PR shortly.

@xuanyang15 please assign me (@a2105z) if that helps with routing — I don't have self-assign permissions on this repo.

[a2105z]

PR ready for review: #6703

Implements metadata-server defaults for unset GOOGLE_CLOUD_PROJECT / GOOGLE_CLOUD_LOCATION / enterprise-Vertex mode on GCP (explicit .env/shell still wins).

@xuanyang15 @steren @klateefa — would appreciate a look when you have bandwidth.

[a2105z]

@xuanyang15 — PR is up for your review: #6703