Google Cloud Solution Architecture Guide

Executive Overview

This document serves as the comprehensive reference architecture guide for migrating an event-driven application from a legacy pre-existing environment to a highly available, serverless Google Cloud architecture.

Source vs Target Architecture (Before & After)

Before: Pre-existing Source Environment

flowchart TD
    Client[External Client] -->|HTTP/HTTPS| NginxProxy[Legacy NGINX Proxy]
    NginxProxy --> MonolithApp[Monolithic Application VM]
    MonolithApp --> LocalDB[(Self-Hosted PostgreSQL)]
    MonolithApp --> LocalQueue[Local RabbitMQ Queue]

After: Target Google Cloud Architecture

flowchart TD
    Client[External HTTPS Client] -->|HTTPS POST /events| CloudRun[Google Cloud Run Service]
    CloudRun -->|Publish Event| PubSubTopic[Cloud Pub/Sub Topic]
    CloudRun -->|Write Raw Payload| GCSAudit[Cloud Storage Audit Bucket]
    PubSubTopic -->|Push Delivery| EventConsumer[Cloud Run Consumer Service]
    EventConsumer -->|Acknowledge| PubSubTopic

Functional requirements

See docs/requirements.md. Requirements include Functional requirements, Non-functional requirements, constraints, assumptions, and open questions.

Accept authenticated HTTPS requests from external clients.
Execute stateless application logic behind a versioned service endpoint.
Asynchronously publish domain events to Pub/Sub.
Retain raw payload records in Cloud Storage for audit and replay.

Selected products

Compute: Google Cloud Run
Messaging: Google Cloud Pub/Sub
Storage: Google Cloud Storage & Firestore
Identity & Access: Google Cloud IAM Service Accounts

Architecture Diagram (Mermaid)

flowchart TD
    Client[External HTTPS Client] -->|HTTPS POST /events| CloudRun[Google Cloud Run Service]
    CloudRun -->|Publish Event| PubSubTopic[Cloud Pub/Sub Topic]
    CloudRun -->|Write Raw Payload| GCSAudit[Cloud Storage Audit Bucket]
    PubSubTopic -->|Push Delivery| EventConsumer[Cloud Run Consumer Service]
    EventConsumer -->|Acknowledge| PubSubTopic

Infrastructure Blueprint (Terraform)

# Google Cloud Solution Architecture Baseline
terraform {
  required_version = ">= 1.5.0"
  required_providers {
    google = {
      source  = "hashicorp/google"
      version = "~> 5.0"
    }
  }
}

provider "google" {
  project = var.project_id
  region  = var.region
}

# Cloud Run v2 Service
resource "google_cloud_run_v2_service" "app_service" {
  name     = "${var.environment}-app-service"
  location = var.region

  template {
    containers {
      image = var.container_image
      ports {
        container_port = 8080
      }
    }
  }
}

# Pub/Sub Topic for Event Ingestion
resource "google_pubsub_topic" "event_ingestion" {
  name = "${var.environment}-event-ingestion-topic"
  labels = {
    environment = var.environment
    managed_by  = "terraform"
  }
}

# Cloud Storage Bucket for Event Replay Audit
resource "google_storage_bucket" "audit_bucket" {
  name                        = "${var.project_id}-${var.environment}-audit-bucket"
  location                    = var.region
  force_destroy               = false
  uniform_bucket_level_access = true

  versioning {
    enabled = true
  }

  lifecycle_rule {
    condition {
      age = 30
    }
    action {
      type = "Delete"
    }
  }
}

# Least-Privilege IAM Service Account
resource "google_service_account" "ingress_sa" {
  account_id   = "${var.environment}-ingress-sa"
  display_name = "Cloud Run Ingress Identity"
}

resource "google_pubsub_topic_iam_member" "publisher_binding" {
  topic  = google_pubsub_topic.event_ingestion.name
  role   = "roles/pubsub.publisher"
  member = "serviceAccount:${google_service_account.ingress_sa.email}"
}

Validation results

Validation Results

Summary

Overall Validation Status: PASS
Mermaid Diagram Syntax: PASS
Terraform Structural Check: PASS
Resource Provisioning Triggered: False (Static non-deployment check enforced)

Verification Rules Checklist

Functional & Non-functional requirements specified
Product selection deferred during discovery and resolved in design phase
Regional High Availability and Security IAM boundaries configured
Mermaid diagram follows valid graph syntax
Terraform HCL declares provider, resources, and least-privilege IAM bindings

Verification Checklist

Step 4 guide persistence: non-empty solution-architecture-guide.md.
Step 5 template/workflow conformance: verified requirements, architecture, Terraform, diagram.
Step 6 & 7 publication & remote verification: complete.

Deployment & Operations Runbook

Initialize Terraform: terraform init
Validate Configuration: terraform plan -var="project_id=YOUR_PROJECT_ID"
Deploy Blueprint: terraform apply

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