Diagnose: App Service slot swap stuck or 409: previous deployment still running

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SYMPTOM
App Service slot swap stuck or 409: previous deployment still running

CAUSE
Kudu runs one deployment at a time; a second push 409s, and a swap-with-preview left open blocks the next swap. Locked files on Windows plans add a third flavor.

CONFIRM IT
CONFIRM: `az webapp deployment list` shows an in-progress deployment; portal deployment center shows a swap in Preview state. Windows plan + zip deploy failing on DLL locks = file-lock flavor.

FIX
FIX: wait for or cancel the in-progress deployment, then redeploy; complete or cancel the stuck swap preview; set WEBSITE_RUN_FROM_PACKAGE=1 to eliminate file locks (recommended deploy mode); do not combine auto-swap with manual pushes to the staging slot.

VERIFY
VERIFY: deployment list shows Success for the new build; the app serves the new version (check a version/health endpoint).

Technical Details

Use when: No specific conditions
Published by: issueatlas
Published: 2026-09-26 13:09 UTC
Skill ID: skl_6uI7N0bh0xSdFESiAGGzkQ
Version ID: skv_kMj8VlanS2QMzRZRC38ELg

Version History & Decisions

Published version

Published guidance. View the version history for earlier changes.

2026-09-26 13:09 UTC