BigQuery & Google Sheets: Adding Drive.readonly Scope

by Alex Johnson 54 views

Understanding the Need for drive.readonly Scope in BigQuery ADC Initialization

When working with BigQuery and external Google Sheets, a common challenge arises when trying to access these sheets from within a Kubernetes environment. BigQuery, Google's fully-managed, serverless data warehouse, allows you to query data stored in various external sources, including Google Sheets. However, to successfully query these external sheets, proper authentication and authorization are crucial. This often involves dealing with Application Default Credentials (ADC) and ensuring the correct scopes are included. In this comprehensive guide, we will delve into why the drive.readonly scope is essential, how it impacts the GenAI Toolbox, and potential solutions for Kubernetes deployments.

The Role of Application Default Credentials (ADC)

Application Default Credentials (ADC) is a strategy used by Google Cloud client libraries to automatically find credentials. This allows your application to authenticate without requiring you to manually manage service account keys or other credentials. ADC checks for credentials in the following order:

  1. The GOOGLE_APPLICATION_CREDENTIALS environment variable.
  2. The service account attached to the Compute Engine, Google Kubernetes Engine (GKE), Cloud Functions, App Engine, or Cloud Run environment.
  3. User credentials from the Google Cloud CLI (gcloud).

In many local and development environments, using gcloud auth application-default login to set ADC works seamlessly. However, in a Kubernetes environment, this interactive flow is not feasible, making it necessary to rely on Workload Identity or mounted service account keys. This is where the challenge of ensuring the correct scopes are included becomes apparent.

The BigQuery and Google Sheets Integration Challenge

When BigQuery attempts to query an external table backed by Google Sheets, it requires a token with the appropriate Google Drive scope. This is because BigQuery needs permission to read the data from the Google Sheet. The error “Access Denied: BigQuery ... Permission denied while getting Drive credentials” indicates that the necessary Drive scope is missing from the ADC.

In local environments, explicitly setting ADC scopes using the gcloud auth application-default login command with the https://www.googleapis.com/auth/drive.readonly scope, alongside other necessary scopes like https://www.googleapis.com/auth/bigquery and https://www.googleapis.com/auth/cloud-platform, resolves the issue. However, in Kubernetes, customizing ADC scopes is not as straightforward.

GenAI Toolbox and the Missing Drive Scope

The GenAI Toolbox, a collection of tools and libraries designed to facilitate generative AI workflows, utilizes BigQuery as a data source. When the Toolbox queries BigQuery, it relies on ADC to authenticate. The relevant code snippet from the Toolbox’s bigquery.go file illustrates this:

cred, err := google.FindDefaultCredentials(ctx, bigqueryapi.Scope)

This line of code retrieves ADC with only the bigqueryapi.Scope (https://www.googleapis.com/auth/bigquery), omitting the crucial drive.readonly scope. As a result, queries to external Google Sheets fail in Kubernetes environments where ADC is derived from the environment (Workload Identity or mounted service account key).

Why drive.readonly is Essential

The drive.readonly scope grants read-only access to the user's Google Drive files. When BigQuery queries a Google Sheet, it needs this scope to fetch the data. Without it, BigQuery cannot access the sheet, leading to the “Access Denied” error. Understanding this dependency is key to troubleshooting and resolving authentication issues in Kubernetes deployments.

Proposed Solution: Adding drive.readonly Scope

To address the issue of missing drive.readonly scope in Kubernetes environments, a potential solution is to modify the GenAI Toolbox code to include this scope when retrieving ADC. Specifically, the line:

cred, err := google.FindDefaultCredentials(ctx, bigqueryapi.Scope)

could be changed to:

cred, err := google.FindDefaultCredentials(
    ctx,
    bigqueryapi.Scope,