GCP Professional Cloud Architect Practice Question

Your company runs a Spring Boot REST API on a single-zone managed instance group behind an external HTTP(S) load balancer in us-central1. After a recent zone-wide outage, management now requires at least 99.95 % availability and wants to eliminate all virtual-machine patching tasks. The traffic pattern is bursty but remains low most of the day, so reducing steady-state compute cost is important. Which architecture change best satisfies the new objectives while keeping ongoing costs as low as possible?

Containerize the service and deploy it to Cloud Run (fully managed) in two nearby regions behind a global external HTTP(S) load balancer, configuring one minimum instance per region.
Convert the instance template to preemptible VMs and move to a regional managed instance group spanning two zones behind the existing external HTTP(S) load balancer.
Deploy the API to App Engine flexible environment with manual scaling of two instances per region and use Cloud DNS latency-based routing across regions.
Migrate the application to GKE Autopilot with clusters in two regions, enable multi-cluster ingress, and run the workload on spot VMs for cost savings.

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Answer Description

Cloud Run (fully managed) provides a 99.95 % monthly availability SLA per region and completely abstracts VM management, so there is no operating-system patching burden. Deploying the service as a container to Cloud Run in more than one region and fronting it with the platform's global external HTTP(S) load balancer delivers cross-regional failover that meets the 99.95 % availability target. Setting a single minimum instance in each region keeps idle-time charges very low because additional instances are started only when traffic increases.

Using preemptible or spot VMs in regional managed instance groups reduces cost but offers no availability SLA and still requires image maintenance. GKE Autopilot reduces some operational work but incurs higher baseline costs than Cloud Run and still needs cluster management. App Engine flexible requires per-instance billing even when idle, so its steady-state cost is higher than Cloud Run with minimal instances. Therefore, the Cloud Run approach offers the required availability and operational simplicity at the lowest steady-state cost.

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