Agent Platform Architecture skill

Gemini platform Architecture and Engineering Guide

This skill is the reference system for designing, engineering, and validating enterprise-grade Gemini platform architectures across multi-project hierarchies, hybrid/cross-cloud networks, zero-trust identity boundaries, and inline safety/policy enforcement planes.

Usage Attribution

MUST READ: Before executing any gcloud, REST API, or MCP command, you MUST read and follow the instructions in Usage Attribution.

[!IMPORTANT] Architectural Scope and Reference Discipline: Use SKILL.md to select the target topology, egress mode, ingress pattern, and governance plane, then consult the authoritative references/*.md manual for exact CLI commands, REST/YAML schemas, Common Expression Language (CEL) expressions, and Python Agent Development Kit (ADK) runtime code (references/*.md is the single source of truth for all implementation syntax). When remote Model Context Protocol (MCP) tools (such as the Google Developer Knowledge MCP server or Google-managed MCP endpoints) are available, prefer remote MCP tool invocation over raw CLI/REST commands. Do not execute unrequested live mutations against customer projects when asked for architectural designs.

[!CAUTION] Human Approval Gate for Sensitive Operations: Always prompt the user for explicit confirmation before executing commands or applying configurations that grant permissive Identity and Access Management (IAM) bindings (roles/iap.egressor, roles/compute.networkUser, roles/networkservices.admin), modify Organization Policies (constraints/iam.managed.disableAccessPolicyBinding), update Unified Access Policy (UAP) or VPC Service Controls (VPC-SC) policies, or delete resources (REST DELETE ...?force=true or CLI --quiet).

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Prerequisites, Authentication, Region, and Billing Setup

1. Google Cloud SDK, Authentication, and Project Setup:

   • Install the Google Cloud SDK (gcloud) and authenticate CLI and Application Default Credentials (gcloud auth login && gcloud auth application-default login, or set GOOGLE_APPLICATION_CREDENTIALS).

   • Select or create the target project (gcloud projects create {project_id} / gcloud config set project {project_id}), set the default region (gcloud config set compute/region {region}, defaulting to us-central1; see Google Cloud Locations), and enable required APIs:

     gcloud services enable aiplatform.googleapis.com agentregistry.googleapis.com \
       agentidentity.googleapis.com agentidentitycredentials.googleapis.com \
       networkservices.googleapis.com networksecurity.googleapis.com iap.googleapis.com \
       modelarmor.googleapis.com compute.googleapis.com dns.googleapis.com \
       certificatemanager.googleapis.com servicenetworking.googleapis.com
     

2. Billing, Least-Privilege IAM, and Product Terminology:
   • Verify an active billing account is attached (gcloud billing projects describe {project_id} --format="value(billingEnabled)") across {host_project_id}, {gov_project_id}, {runtime_project_id}, and {mcp_project_id} (required even when evaluating free-tier allowances; review Google Cloud Pricing).
   • Grant explicit least-privilege IAM roles (roles/aiplatform.user, roles/networkservices.admin, roles/compute.networkAdmin, roles/compute.networkUser, roles/iap.egressor, or a custom role with networkservices.agentGateways.get,networkservices.agentGateways.use,networkservices.operations.get) rather than primitive roles/owner or roles/editor.
   • Use approved product names: Gemini platform, Agent Runtime (reasoningEngines), Agent Gateway (240.0.0.2:443), Agent Connectivity Template (ACT), Agent Registry, and Unified Access Policy (UAP Policy V2) / Semantic Governance Policy (SGP).

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3-Phase Architect Workflow and Decision Tree

graph TD
    Start["Enterprise Gemini platform Architecture"] --> Q1{"1. Egress Destinations?"}
    Q1 -->|"RFC 1918 + Google APIs Only"| Priv["ACT: vpcEgress = PRIVATE_RANGES_ONLY<br/>• Direct Private Google Access (PGA)"]
    Q1 -->|"Public Internet, VPC-SC, or Non-RFC 1918 PUPI"| All["ACT: vpcEgress = ALL_TRAFFIC<br/>• 100% Egress via AGW VIP 240.0.0.2:443<br/>• Consolidate Core Google APIs FQDNs"]
    All --> Q2{"2. Layer 7 URL List or Cross-Cloud mTLS?"}
    Q2 -->|"No (Standard NAT)"| Nat["Direct Cloud NAT on PSC-I Subnet<br/>• ENDPOINT_TYPE_VM,ENDPOINT_TYPE_SWG"]
    Q2 -->|"Yes (Next-Hop SWP)"| Swp["Next-Hop SWP (NEXT_HOP_ROUTING_MODE) + PBR<br/>• Internal and Google API DEFAULT_ROUTING bypasses<br/>• Default route via SWP ILB IP<br/>• Exclude PSC-I from manual Cloud NAT"]

1. Phase 1 — Scope Verification and Architecture Discovery:
   • Scope Boundaries and Single-Region Discovery: Decline generic Google Cloud IAM/Compute/Storage debugging unrelated to the Gemini platform stack or requests to run broad multi-region live project scanning loops, pointing instead to gcloud ai reasoning-engines list --region={region}.
   • Architecture Design and Engineering: Identify the project hierarchy (Host, Governance Hub, Runtime Spoke, Tool/MCP Spoke), egress mode (ALL_TRAFFIC vs PRIVATE_RANGES_ONLY), policy plane (UAP V2, SGP, Model Armor), and target output format (topology specification, gcloud CLI commands, or REST/YAML manifests).
2. Phase 2 — Draft Architecture Plan and Resource Mapping:
   • Synthesize the topology diagram, project/VPC layout, IAM bootstrap matrix, and security controls using the Domain Router and Symptom Matrix, and map each manual's canonical REST/YAML schema and CLI commands into the target deployment artifacts.
3. Phase 3 — Post-Deployment and Audit Log Verification:
   • Pair every architecture design with the Post-Deployment and Cloud Audit Log Verification checklist (references/topologies_and_project_layouts.md) and runtime query validation (references/agent_runtime_and_identity.md).

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Domain Router and Symptom Matrix

Each reference manual in references/ is the single source of truth for its domain's CLI commands, REST/YAML schemas, quotas, and CEL expressions. Always read the corresponding reference manual before generating configurations or answering domain-specific questions:

Architecture Domain	Topics and Architectural Decisions Covered	Symptoms and Failure Modes Routed Here	Canonical Reference Manual
1. Project Hierarchy, Shared VPC, VPC-SC, and Custom Routing	Multi-project separation (Host, Governance Hub, Runtime Spoke, Tool/MCP Spoke), PSC-I subnet sizing, cross-project Service Agent IAM bootstrap, VPC-SC perimeters, non-RFC 1918 PUPI/peered custom route exchange, and post-deployment Cloud Audit Log verification.	PSC-I IP exhaustion, cross-project attachment or addressGroup permission denials, VPC-SC perimeter blocks, dropped non-RFC 1918 internal routes, or post-deployment verification.	references/topologies_and_project_layouts.md
2. Agent Connectivity Template (ACT) and Agent Gateway	Choosing ALL_TRAFFIC vs PRIVATE_RANGES_ONLY, ACT and Agent Gateway REST/YAML schemas, control-plane URI formatting, registry attachment limits, and container custom Root CA bundle trust.	Control-plane URI validation errors, registry attachment limit errors, or container TLS verification failures ([SSL: UNEXPECTED_EOF_WHILE_READING]).	references/agent_gateway_and_act.md
3. Outbound Routing, Next-Hop SWP, PBR, and Hybrid mTLS	Source-range Policy-Based Routes (PBR) for PSC-I subnets, Next-Hop Secure Web Proxy (NEXT_HOP_ROUTING_MODE), swg-autogen-nat vs manual Cloud NAT coexistence, gRPC/A2A/WebSocket routing, Spanner SA impersonation, and Cross-Cloud mTLS Egress Hubs (Hybrid NEG).	Asymmetric return-routing drops between manual Cloud NAT and swg-autogen-nat, outbound URL filtering on PSC-I interfaces, or cross-cloud mTLS origination over Cloud Interconnect/VPN.	references/egress_routing_and_swp.md
4. Ingress ALB, URL Rewrites, Private CA, and 3P IdP STS	Two-Tier and Single-Tier ALB ingress with URL Map hostRewrite/pathPrefixRewrite, Private CA TrustConfig with Regional Internal ALB + Serverless NEG for Cloud Run MCP servers, and 3P IdP (EntraID/Ping/Okta) token exchange via LbTrafficExtension (ext_proc + STS).	WebPKI root stripping (NO_ADDITIONAL_ROOTS), empty :authority drops on Serverless NEGs, *.run.app Google-managed certificate mismatches, or OAuth/IAP header collisions.	references/ingress_patterns_and_rewrites.md
5. UAP Policy V2, IAP V1, SGP, and Model Armor Governance	Organization/Folder/Project UAP Policy V2 and IAP V1 CEL authorization rules, Semantic Governance Policy (SGP CONTENT_AUTHZ), custom AuthzExtension / AuthzPolicy targets, and fail-closed Model Armor Floor Settings, templates, and ADK callbacks.	Egress request is not authorized (HTTP 403 / status.code=7) on MCP initialize or tools/list, failed to parse the service URL on AuthzExtension, binary gRPC parser crashes, or fail-open safety bypasses.	references/governance_security_policies.md
6. Agent Registry, Consolidated googleapis, and Federation	Consolidating core Google APIs FQDNs into a single googleapis service (ALL_TRAFFIC), registering MCP/A2A/REST services, extracting server-generated registryResource UUIDs for roles/iap.egressor, and Event-Driven Spoke-to-Hub Registry Federation.	ALL_TRAFFIC agent startup or telemetry blackholing, IAM binding target mismatches on Registry resources, OpenAPI/MCP spec size rejections, or multi-project catalog drift.	references/registry_and_federation.md
7. ADK Runtime Packaging, Agent Identity, and Day-2 Operations	Packaging ADK agents with AGENT_IDENTITY (SPIFFE) and Auth Manager, regional residency, BigQuery pre-execution cost guards, in-place ACT updates, reverse-dependency teardown, and external Cloud NAT IP verification.	Raw credential exposure, HTTP 409 ABORTED control-plane mutex locks, HTTP 400 FAILED_PRECONDITION (FROM_AGENT_GATEWAY* or contains child resources: sessions), or X-Forwarded-For: 0.0.0.0 when probing *.run.app.	references/agent_runtime_and_identity.md

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Supporting Public Documentation Links

• Agent Runtime Overview
• Agent Gateway Overview
• Policies Overview
• Agent Identity Overview
• Agent Registry Overview
• Deploy Agent Gateway Runtime
• Private Service Connect Interface