Share via

Azure App Service outage after deployment and failed backup restore – certificate not loading due to thumbprint mismatch

Coen Claus 1 Reputation point
2026-06-10T14:39:07.13+00:00

We recently experienced an outage in an Azure App Service–based authentication service after a deployment. I’m trying to understand what went wrong and how to prevent similar issues in the future.

Scenario

  • A deployment was performed to a production App Service environment.
  • Shortly after deployment, the application started returning HTTP 500/503 errors and authentication stopped working.
  • Existing sessions continued to work for some time, but new sign-ins and token renewals failed.

Troubleshooting steps taken

  • Multiple attempts were made to restore the App Service from a backup (including site configuration).
  • The restore process did not resolve the issue.
  • Application settings and environment variables were reviewed.
  • Eventually, it was discovered that a certificate could not be loaded due to a mismatch in the value of an environment variable (WEBSITE_LOAD_CERTIFICATES).
  • The mismatch was a single-character difference in the certificate thumbprint.
  • After correcting the value manually, the service recovered.

Observations

  • The issue was difficult to detect because the thumbprint values are long hexadecimal strings.
  • Visual inspection alone did not help identify the mismatch early.
  • Backup restore did not appear to revert the misconfigured environment variable.
  • The misconfiguration originated from infrastructure-as-code parameter values.

Questions

Backup & Restore behavior

  • Should Azure App Service backup/restore include environment variables like WEBSITE_LOAD_CERTIFICATES?
    • Under what circumstances would these settings not be restored?
  • Certificate handling
    • Is using certificate thumbprints in app settings considered a best practice, or are there more robust alternatives (e.g., Key Vault integration)?

Any guidance or best practices would be appreciated.

Azure Static Web Apps
Azure Static Web Apps

An Azure service that provides streamlined full-stack web app development.

1 answer

Sort by: Most helpful
Most helpful Newest Oldest
  1. Sina Salam 30,166 Reputation points Volunteer Moderator
    2026-06-15T12:57:45.1333333+00:00

    Hello Coen Claus,

    Welcome to the Microsoft Q&A and thank you for posting your questions here.

    I understand that your Azure App Service outage after deployment and failed backup restore – certificate not loading due to thumbprint mismatch.

    Your outage was caused by a bad IaC-supplied WEBSITE_LOAD_CERTIFICATES thumbprint. The manual correction fixed production, but the durable fix is to correct the IaC source, stop manually typing thumbprints, add a pipeline gate that verifies the configured thumbprint against the actual App Service certificate, deploy first to a staging slot, run a certificate/authentication smoke test, and only then swap to production. Do not depend on App Service backup restore as the primary rollback for this class of issue, and make sure you use slots and deterministic IaC rollback, and use restore only through a tested slot-based recovery runbook.

    Use the below for more reading and steps:

    I hope this is helpful! Do not hesitate to let me know if you have any other questions, steps or clarifications.

    Please don't forget to close up the thread here by upvoting and accept it as an answer if it is helpful.

    Was this answer helpful?

Your answer

Answers can be marked as 'Accepted' by the question author and 'Recommended' by moderators, which helps users know the answer solved the author's problem.