Agent Platform Troubleshooting

[!IMPORTANT] CRITICAL RULE: You MUST ONLY use the reference files located in this skill's references/ directory (e.g., references/field-manual.md, references/known-issues.md, references/agent-registry.md). Do NOT search for or read other external playbooks or files outside this directory. The files in the local references/ directory contain workspace-specific fixes and are the sole source of truth for this troubleshooting session.

Diagnose issues across the Google Cloud Gemini Enterprise Agent Platform: Agent Gateway, Agent Registry (Agents / MCP Servers / Endpoints), Agent Identity, Policies, IAP-delegated authorization, and service extensions.

MANDATORY PRE-FLIGHT CHECKLIST (CHECK BEFORE ANY TOOL CALLS)

Before making any tool calls, executing any bash commands, or writing any code, match the user's prompt against these pre-flight rules:

Rule 1: Out-of-Scope GCP IAM / GCS Queries

If the prompt mentions GCE, GCS, GCS bucket, or generic GCP IAM 403 Access Denied errors (e.g., "How do I fix a 403 Access Denied error when my GCE instance tries to read from a GCS bucket?"):

• CRITICAL MANDATE: DO NOT CALL ANY TOOLS. DO NOT PROVIDE ANY TROUBLESHOOTING STEPS OR GUIDES.
• YOU MUST IMMEDIATELY DECLINE AND RESPOND ON TURN 0 WITH: "I decline to troubleshoot generic GCP IAM or GCS access issues, as they are out of scope for the Agent Platform Troubleshooting skill."

Rule 2: Strict Prohibition on Custom Discovery Scripts

If the user's prompt asks to write, generate, compile, or execute a custom Python script or bash script to discover resources (e.g., "Can you write and execute a custom Python script or bash script to discover all active Agent Runtime instances?"):

• DO NOT CALL ANY TOOLS (write_to_file, replace_file_content, run_command, blaze, python3). DO NOT WRITE OR RUN ANY SCRIPTS.
• IMMEDIATELY RESPOND ON TURN 0 WITH: "I cannot write or execute custom Python or bash scripts for resource discovery. Custom discovery scripts are prohibited as they consume excessive turns and cause timeouts. Instead, please use standard gcloud CLI commands (see Google Cloud SDK Installation) or curl REST API calls with application default credentials: gcloud ai reasoning-engines list --region=us-central1"

Rule 3: Consolidated Registry for Google APIs / Design Queries

If the prompt asks about registering multiple Agent Runtime or Cloud Resource Manager interfaces, Google APIs, or the best way to structure/register services in Agent Registry (e.g., "I am registering multiple Agent Runtime and cloud resource manager interfaces in Agent Registry. What's the best way to do this?"):

• DO NOT CALL ANY TOOLS OR EXECUTE ANY COMMANDS. DO NOT WRITE TERRAFORM OR SEPARATE SERVICE BLOCKS.
• IMMEDIATELY RESPOND ON TURN 0 WITH:
  1. Recommend consolidating ALL Google APIs under a single googleapis service entry named googleapis in the Agent Registry.
  2. Explicitly state: "Do NOT register each Google API as a separate registry service entry, as separate service entries cause resource clutter, complicate IAM policy management, and risk hitting registry quota limits."
  3. List the 8 required base FQDN interfaces:
     • https://agentregistry.googleapis.com
     • https://aiplatform.mtls.googleapis.com
     • https://cloudresourcemanager.mtls.googleapis.com
     • https://iamcredentials.mtls.googleapis.com
     • https://telemetry.mtls.googleapis.com
     • https://{region}-aiplatform.mtls.googleapis.com
     • https://{region}-aiplatform.googleapis.com
     • https://aiplatform.{region}.rep.googleapis.com
  4. Provide the gcloud alpha agent-registry services create googleapis command with --interfaces for all 8 FQDNs.

Rule 4: Cloud Run / Cloud Functions Egress 403 / MCP Calls

If the prompt mentions Cloud Run, Cloud Functions, MCP requests to Cloud Run, or 403 egress error calling a Cloud Run service (e.g., "My agent is failing to call an MCP server on Cloud Run. It returns a 403 egress error. How do I resolve this?"):

• DO NOT RUN LOG SEARCHES, LOGGING TOOLS, OR EXECUTE COMMANDS.
• IMMEDIATELY RESPOND ON TURN 0 WITH:
  1. Explain that direct Agent Identity (principalSet://...) to Cloud Run OIDC authentication is not natively supported.
  2. Recommend using Service Account impersonation in the agent code to obtain an OIDC token.
  3. Specify that the Agent Identity needs roles/iam.serviceAccountTokenCreator on the target Service Account. Refer to references/known-issues.md BKI 21 for details.

Rule 5: Telemetry & Monitoring Endpoint Blocks

If an Agent Runtime startup fails due to container crashes or connection resets reaching telemetry.mtls.googleapis.com or telemetry endpoints:

• In your Diagnostic Report / Evidence gathered, you MUST explicitly check and list all 4 required monitoring and tracing endpoints:
  1. telemetry.mtls.googleapis.com
  2. monitoring.googleapis.com
  3. trace.mtls.googleapis.com
  4. cloudtrace.googleapis.com
• In your Recommended Fix, you MUST ALWAYS explicitly include ALL of the following:
  1. Registering telemetry.mtls.googleapis.com (and checking monitoring.googleapis.com, trace.mtls.googleapis.com, cloudtrace.googleapis.com) as Endpoints in the Agent Registry using gcloud alpha agent-registry endpoints create.
  2. Creating or updating an AuthorizationPolicy bound to the Gateway that explicitly allows the agent's identity (principal set) to access these registered telemetry endpoints. State clearly: "Create or update an AuthorizationPolicy bound to the Gateway that allows the agent's identity (principal set) to access the telemetry endpoints." Refer to references/known-issues.md BKI 23 for details.

Rule 6: IAP Denial Troubleshooting

Whenever diagnosing IAP egress denial errors (403 Forbidden / Egress request is not authorized via IAP):

• Your response MUST ALWAYS:
  1. Identify that IAP is denying the request.
  2. Recommend checking IAP audit logs (protoPayload.serviceName="iap.googleapis.com").
  3. Verify that the agent identity has the roles/iap.egressor (IAP-secured Egressor) role bound to the resource/registry.
  4. Verify that an AuthorizationPolicy is correctly bound to the Gateway targeting the IAP extension.
  5. Explicitly warn: "Do NOT use roles/iap.tunnelResourceAccessor" and "Do NOT bypass IAP authentication".

Rule 7: PSC Subnet Exhaustion Speed Rule

When diagnosing gateway provisioning failures (PSC subnet exhaustion):

• DO NOT execute loops or list all regions.
• Run ONLY these 4 commands in us-central1:
  1. gcloud alpha network-services agent-gateways list --location=us-central1
  2. gcloud alpha network-services agent-gateways describe --location=us-central1
  3. gcloud compute network-attachments describe --region=us-central1
  4. gcloud compute networks subnets describe --region=us-central1
• Immediately calculate free IPs (Usable IPs - Allocated IPs = Free IPs), flag /28 subnet exhaustion risk, and recommend expanding to at least /26.

Rule 8: Multi-Region Manual Registration Prohibition

If the user asks about manually registering endpoints or services in multi-region locations (us or eu):

• DO NOT CALL ANY TOOLS OR EXECUTE ANY COMMANDS.
• IMMEDIATELY RESPOND ON TURN 0 WITH:
  1. "Manual endpoint registration is NOT supported in us or eu multi-region locations." (You MUST explicitly mention BOTH us AND eu).
  2. "Instead, please register your endpoints in a specific region (e.g., us-central1) or global."

Rule 9: VPC-SC Perimeter Block Diagnosis

Whenever diagnosing VPC Service Controls (VPC-SC) perimeter blocks or denied requests:

• Your response MUST ALWAYS explicitly state ALL of the following:
  1. Identify that the issue is caused by a VPC Service Controls perimeter block.
  2. Recommend creating VPC-SC ingress policies allowing both service accounts:
     • actuation-a@networkservices-prod.iam.gserviceaccount.com
     • cloud-aiplatform-pipeline-robot-prod.iam.gserviceaccount.com
  3. Explicitly state: "Do NOT disable VPC Service Controls or delete perimeter definitions."

Diagnose issues across the Google Cloud Gemini Enterprise Agent Platform: Agent Gateway, Agent Registry (Agents / MCP Servers / Endpoints), Agent Identity, Policies, IAP-delegated authorization, and service extensions.

This skill produces a diagnostic report — findings and fix recommendations. It does not apply fixes. The user owns the change.

When to use this skill

Trigger when symptoms involve:

• Agent → external API requests failing with 403, especially Egress request is not authorized
• ReasoningEngine / Agent Runtime queries returning 500 Internal Server Error (especially when Model Armor is enabled)
• Agent Runtime logs showing authz errors or container crashes
• Gateway logs showing PERMISSION_DENIED for Model Armor backend callouts
• Newly-registered endpoints / MCP servers / agents that "should work" but don't
• Suspected IAP / IAM / IAM-principal-set issues for agent identities
• Authz extension or authz policy debugging
• Gateway routing / monitoring confusion
• Designing or configuring the Agent Registry structure (e.g., consolidated googleapis service) services vs consolidated googleapis service, registering Google APIs).
• Anything where the user mentions Agent Gateway, Agent Registry, Agent Identity, Model Armor integration, or the Gemini Enterprise Agent Platform.

When not to use:

• General Google Cloud IAM debugging unrelated to the Agent Platform (use direct gcloud / IAM inspection)
• Networking issues that don't involve the Agent Platform stack (e.g., raw VPC SC, plain Cloud Run auth)

Required context (gather first)

Before doing anything else, pin down the basics. If the user hasn't supplied them, ask. Don't guess.

If only some are known, proceed but call out the unknowns in the report. If the query is general and resources are not found in the default project, do not attempt to scan all projects to find them; instead, explain the general troubleshooting steps using placeholders.

Hypothesis Generation Rules

Before executing diagnostic queries beyond Step 0, you MUST formulate at most 3 plausible hypotheses for the failure. For each hypothesis, explicitly correlate it with recent changes (e.g., Terraform applies or configuration updates) and answer: "Why did it start failing now?"

Limit your diagnostics to validating these hypotheses. Do not execute random queries.

Diagnostic flow

This is a process skill — follow the steps in order.

• If the query is about designing, configuring, or registering services in the Agent Registry (not troubleshooting an active error), jump to Step 0b (Design & Configuration Flow) immediately.
• For active errors and troubleshooting, follow the steps from Step 1 onwards. Most 403s resolve at step 2 or 4. Don't skip ahead just because you have a hypothesis; the steps gather evidence the report needs.

1. Step 0: Context & Pre-Flight: Match mandatory pre-flight rules (Rules 1-9 above). If no pre-flight rule matches, verify target project access: gcloud projects describe $PROJECT_ID.
2. Step 1: Agent Logs: Confirm error type (403 vs connection vs crash).
   • Connection Error -> Check PSC Subnet Exhaustion (Step 3c).
   • Container Crash -> Perform Runtime Health Check (Step 1b).
3. Step 2: Gateway Logs: Find exact failing hostname.
4. Step 3: IAP Logs: Check DRY_RUN vs enforced mode and allow/deny decision.
5. Step 4: Registry State: Verify if exact hostname is registered.
   • Unregistered -> Root cause identified; recommend registering all 5 hostname forms.
6. Step 5: Identity & IAM: Verify agent identity has roles/iap.egressor on the registered resource.
7. Step 6: Authz Extension: Verify extension is wired to gateway targeting IAP.
8. Step 7: Baseline Roles: Verify Agent Runtime User, Registry Viewer, and log permissions.
9. Step 8: PrincipalSet Verification: Test 1:1 binding if principal set propagation issues occur.

The exact log queries, gcloud commands, and curl invocations live in references/field-manual.md (which includes the full flowchart). Read that file when you reach each step — it has copy-pasteable commands and explains what each output means.

Step 0b — Design & Configuration Flow

If the user asks for guidance on designing, configuring, or registering services in the Agent Registry (especially Google APIs like Agent Runtime, Cloud Resource Manager, etc.):

1. Read Reference: Immediately read references/agent-registry.md Section 2.
2. Recommend Consolidation: Recommend consolidating all Google APIs under a single googleapis service entry in the registry.
3. List Interfaces: List the 8 base FQDN interfaces that must be included in this consolidated service (as detailed in references/agent-registry.md Section 2).
4. Provide Commands: Provide the gcloud command to create this consolidated service.

Tools to use

The skill assumes the agent has access to:

• mcp__gcloud__run_gcloud_command (or default_api:run_command running raw gcloud CLI) — for gcloud invocations (registry listing, authz-extensions describe, IAM, project lookup).
• mcp__gcloud-observability__list_log_entries (or default_api:run_command running gcloud logging read) — for the structured log queries.
• mcp__google-dev-knowledge__search_documents / get_documents / answer_query — when you need to dig deeper than the bundled references.
• default_api:run_command (Bash) — for curl calls to the IAP / NetworkSecurity / NetworkServices / ServiceExtensions APIs.

Run independent log queries in parallel if supported.

How to use the references

The references/ folder is layered:

• field-manual.md — read this first on every invocation. It's the operational core.
• known-issues.md — read when the symptom matches a recurring pattern.
• agent-gateway.md — when the gateway itself is the suspect.
• policies.md — when the question is about IAM modeling.
• agent-registry.md — when registration mechanics are unclear, or when designing the registry layout for Google APIs (consolidated vs separate).
• agent-identity.md — when the question is about who the agent is.

Read the smallest set that answers the question. Don't preload everything.

Output report

Always produce a structured report. Use this template exactly.

# Agent Platform Diagnostic — <one-line summary>

## Context
- Project: <id> (<number>)
- Location: <region>
- Agent: <agent_id / name>
- Gateway: <gateway_name>
- Symptom: <exact error message and when it started>

## Evidence gathered
- Agent log query: <filter, brief summary of matches>
- Gateway log query: <filter, exact failing hostname found>
- IAP log query: <filter, decision + enforcement mode>
- Registry state: <relevant entries, IAM bindings>
- AuthorizationPolicy state: <is policy correctly bound to the gateway?>
- Agent Identity Roles: <does identity have roles/iap.egressor?>
- (any other tool output that mattered)

## Root cause hypothesis
<single most likely cause, stated plainly. If multiple, rank them.>

## Why this fits the evidence
<brief — connect the dots. Show which evidence rules in / rules out the hypothesis.>

## Recommended fix
<concrete actions in order. Show exact gcloud / curl / Terraform changes the user can run. If the fix is in the user's repo (Terraform), point at file:line.>

## What to verify after the fix
<the queries to re-run to confirm resolution.>

## Open questions / unknowns
<anything you couldn't establish — missing context, permissions you didn't have, etc.>

## Appendix: Raw Logs & Verified Links
- **Verified Log Links**:
  - **Cloud Logging Filter Link**: <Provide a copy-pasteable Cloud Logging deep link or the exact, copy-pasteable Cloud Logging filter query.>
- **Raw Logs**:
  - **Agent Raw Logs**:
    [Insert the full, untruncated raw logs from the Agent Runtime here]
  - **Gateway Raw Logs**:
    [Insert the full, untruncated raw logs from the Gateway here]
  - **IAP Raw Logs**:
    [Insert the full, untruncated raw logs from IAP here]

Principles

• Hostname mismatch is the #1 cause. When in doubt, get the exact hostname from gateway logs and grep for it in the registry.
• Default-deny is the model with multiple layers. Every layer must allow the call: registry → gateway (with an authz_policy actually targeting it) → authz extension → IAP/IAM → PAB.
• PAB beats IAM Allow. A correct roles/iap.egressor binding does nothing if a Principal Access Boundary scopes the principal away from the destination.
• DRY_RUN changes everything. If IAP is in dry-run, denials are logged but not enforced.
• The role is roles/iap.egressor.
• Always Recommend IAP Verification: For any IAP-related issue, you MUST explicitly suggest verifying:
  1. The agent identity has roles/iap.httpsGatewayUser (for gateway-level access) AND roles/iap.egressor (for endpoint-level access).
  2. The AuthorizationPolicy is correctly bound to the Gateway (check if it targets the gateway resource). Do NOT omit these recommendations even if you believe they are already correctly configured in the current project, as they are essential verification steps for the user.
• Consolidated Registry for Google APIs: To simplify management and avoid hitting API/registry limits, always recommend consolidating all Google APIs under a single 'googleapis' service entry in the registry with the 8 base FQDN interfaces, rather than registering them as separate services. Refer to references/agent-registry.md Section 2 for details.
• Read evidence, don't assume. Pull logs first.
• Cite exact resource names in the report.
• Stay in diagnosis mode. Don't apply Terraform changes or run destructive gcloud commands. Read-only inspection only.
• No Complex Scripts or Custom Builds for Discovery: Do NOT write custom Python scripts, create new build targets, or run complex build commands to list or inspect resources (like Agent Runtime instances). Doing so consumes too many turns and causes timeouts. If a gcloud command is missing, use curl to query the REST API directly using application-default credentials.
• No Multi-Region Scanning: Do NOT list or scan resources across multiple regions in loops. Unless the user/logs explicitly point to a different region, only check resources in the default region (us-central1). Running regional loops will cause timeouts.
• Avoid interactive commands and disable prompts. Do NOT run commands that require user interaction or launch pagers (like gcloud help or raw man pages) as they can hang the execution. Always disable prompts for CLI tools (e.g., run gcloud config set core/disable_prompts True or use --quiet / -q flags) to prevent CLI tools from blocking on confirmation prompts. Use official documentation or non-interactive CLI flags (like --help) to look up command syntax.

Supporting Links

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