Root url seems wrong for Google::Apis::AiplatformV1::AiplatformService

[jcoyne]

When I do:

    scope = 'https://www.googleapis.com/auth/cloud-platform'
    Google::Auth.get_application_default([scope])

    vertex_ai_service = Google::Apis::AiplatformV1::AiplatformService.new
    vertex_ai_service.authorization = authorization

    # Project and location details
    project_id = "sul-ai-sandbox"
    location = "us-central1" # Change as appropriate

    # Resource name for the model
    model_id = "text-embedding-004"
    endpoint = "projects/#{project_id}/locations/#{location}/publishers/google/models/#{model_id}"

    response = vertex_ai_service.predict_project_location_publisher_model(
        endpoint,
        request_body
     )

This gives this output, and eventually a 503 error:

Sending HTTP post https://aiplatform.googleapis.com/v1/projects/sul-ai-sandbox/locations/us-central1/publishers/google/models/text-embedding-004:predict?

I noticed the hostname used in the log is not what is listed in https://cloud.google.com/vertex-ai/generative-ai/docs/embeddings/get-text-embeddings#generative-ai-get-text-embedding-drest.

So, it seems to work if I do:

    vertex_ai_service.root_url = "https://us-central1-aiplatform.googleapis.com/"

I didn't see this documented anywhere or if this is the supported way of doing this. In any case it's a challenge to find this invocation.