You need to send a customized email to customers when they place an order in your new ecommerce site while minimizing deployment effort. What should you do?

Creating a Cloud Function triggered by Firestore document create events is the most efficient solution. When a new order is placed, a document is likely created in Firestore. This trigger automatically invokes your Cloud Function, which can then execute code to send a customized email using an email API (e.g., SendGrid, Mailgun). This approach is serverless, minimizing deployment and operational effort. Hosting an email-sending app on Compute Engine would require managing a server, increasing deployment and maintenance overhead. An email notification channel and alerting policy are for operational alerts, not for sending customized customer emails. Using Pub/Sub to send an email when an API returns HTTP 200 OK is less direct; while Pub/Sub could be part of a larger asynchronous system, directly triggering from the Firestore document creation is simpler and more aligned with the requirement.