VMSSInstanceNotFound
Azure returns `VMSSInstanceNotFound` when a requested scale set VM instance ID cannot be resolved in the target scale set context.
Last reviewed: February 3, 2026|Editorial standard: source-backed technical guidance
What Does VMSS Instance Not Found Mean?
Instance-scoped operations fail because the target VMSS member is missing, replaced, or addressed with an invalid identifier.
Common Causes
- -Instance ID is stale after scale-in, image upgrade, or instance replacement.
- -Request targets wrong scale set, subscription, or resource group scope.
- -Automation caches instance IDs and reuses them after rolling operations.
- -Instance was deleted or reimaged and old identifier is no longer valid.
How to Fix VMSS Instance Not Found
- 1List current VMSS instances and confirm target instance ID exists at execution time.
- 2Resolve operations using fresh instance inventory from control plane, not cached IDs.
- 3Validate scale set name/resource group/subscription tuple before issuing instance action.
- 4Retry with updated instance identifier after lifecycle reconciliation.
Step-by-Step Diagnosis for VMSS Instance Not Found
- 1Capture failing instance ID, scale set ID, and operation type from logs.
- 2Query live VMSS instance view to confirm current instance inventory and states.
- 3Correlate failure with recent scale, upgrade, reimage, or repair events.
- 4Retest operation against a currently existing instance after inventory refresh.
Instance Identity and Inventory Validation
- -Resolve live instance IDs from control plane before mutation (example: cached instance
12no longer exists after automatic scale-in). - -Validate scope tuple end to end (example: correct scale set name but wrong resource group in runtime context).
Scale Operation Drift Checks
- -Correlate with recent rolling upgrade or reimage events (example: operation targets replaced instance after automatic repair).
- -Audit automation cache invalidation logic (example: instance list refreshed hourly while scale set changes every few minutes).
How to Verify the Fix
- -Retry operation using fresh instance inventory and confirm success.
- -Validate no further VMSS instance-not-found errors in follow-up scaling actions.
- -Ensure instance-targeted automation uses current IDs across the rollout window.
How to Prevent Recurrence
- -Fetch VMSS instance IDs just-in-time before each instance-scoped operation.
- -Invalidate cached instance mappings on scale, upgrade, and repair events.
- -Use idempotent orchestration that can tolerate instance churn in scale sets.
Pro Tip
- -drive instance actions from instance metadata queries at runtime rather than static queues populated before scale operations.
Decision Support
Compare Guide
403 Forbidden vs 404 Not Found: When to Hide Resources
Use 403 for explicit access denial, or 404 to conceal resource existence when security policy requires reducing endpoint and object enumeration risk.
Compare Guide
404 Not Found vs 410 Gone: Missing vs Permanent Removal
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Playbook
Resource State Playbook (404 / 410 / ResourceNotFound)
Use this playbook to separate temporary missing-resource lookups from permanent removals, then fix scope, lifecycle, and identifier drift safely.
Official References
Provider Context
This guidance is specific to Azure services. Always validate implementation details against official provider documentation before deploying to production.