Enabling WEBSITES_ENABLE_APP_CACHE=true Breaks App Startup on Linux PHP Web App

[musilondrej]

I’m experiencing an issue where enabling WEBSITES_ENABLE_APP_CACHE=true on my Azure Web App (running PHP on Linux) causes the application to fail on startup. The logs indicate that AppCache is enabled but cannot locate the cached build artifact, resulting in a restart loop.

I have tried multiple redeployments using different methods, including GitHub Actions, but the issue persists.

Environment Details:

• Web App Type: Linux (PHP)
• App Service Plan: P1v2
• Region: Germany West Central
• Deployment Method: GitHub Actions
• PHP Version: 8.3

When enabling WEBSITES_ENABLE_APP_CACHE=true, my Web App fails to start. The logs show:
Looks like AppCache is enabled but cannot locate the zipped build artifact. AppCache needs a new deployment.

After setting this environment variable, the app enters a restart loop, and Kudu logs indicate that the cached build artifact is missing. A new deployment does not always resolve the issue.

Disabling WEBSITES_ENABLE_APP_CACHE allows the app to start.

Any guidance on how to properly use WEBSITES_ENABLE_APP_CACHE with PHP Web Apps would be appreciated.

Thank you.

[gg3orgiev]

@musilondrej If you are utilizing deployment slots on Azure Web Apps, I would suggest the following:

1. Start a deployment slot
2. Enable the WEBSITES_ENABLE_APP_CACHE=true on it.
3. Do a deployment
4. Give it a bit of time to warmup as cold starts are affected with this setting.
5. If the deployment slot boots up successfully - swap with Production.

I have had numerous issues with this setting, but this flow has provided to avoid downtimes on my end.