Secure n-tier serverless web application with strict private application tiers

This skill guides agents through the workflow of designing and implementing a secure serverless web application with as many architectural design layers as specified by the user. It uses Cloud Run for the serverless layers and Cloud SQL for PostgreSQL as the data layer. A three-tier web application might be represented in three architectural layers: a Cloud Run presentation layer, a Cloud Run application layer, and a Cloud SQL for PostgreSQL database layer.

The architecture enforces strict physical and network isolation across all tiers (T1 to TN):

• Tier 1 presentation tier (frontend / reverse proxy): Public-facing UI rendering/gateway service (Cloud Run). Exposes the entry point via Cloud Load Balancing and routes requests downstream to internal tiers privately via Direct VPC Egress.
• Tier 2..N application tier (internal microservices / business logic): Private application services (Cloud Run). 100% isolated from the internet (Ingress: VPC-internal, INGRESS_TRAFFIC_INTERNAL_ONLY), reachable exclusively via upstream VPC routing (egress = "ALL_TRAFFIC" with Private Google Access on the subnet for *.run.app URLs, or egress = "PRIVATE_RANGES_ONLY" via an internal Application Load Balancer).
• Data tier: Private Cloud SQL for persistent data and Memorystore for Redis for caching, reachable exclusively from authorized application tiers.