App services having react frontend code says 404 not found

Question

I have been running react app on azure app services. Today one of my team member deployed code and it says unhealthy and return 404 not found on trying to reach the website.

this is diagnostics information provided by web app in azure.

Application evaluated unhealthy due to possible misconfiguration.

Description	We noticed the application has responded back with a 404 (Not Found) status code for the configured health check URL. Status codes outside of 200 to 299 range are considered as failure by health check.
Description	We noticed the application has responded back with a 404 (Not Found) status code for the configured health check URL. Status codes outside of 200 to 299 range are considered as failure by health check.
Recommended action	Please make sure that the health check is set to an existing path. You can verify this by visiting your app at the path you have chosen.

Answer 1

Hi @Rajkumar Das

Thank you for reaching us regarding the issue.

Azure App Service Health Check works by periodically sending HTTP requests to a configured URL path on your application. If that path returns any HTTP status code outside the range 200–299 (including 404), the instance is considered unhealthy.

Microsoft explicitly states:

• There is no default health check path
• The configured path must exist in the application
• 404 (Not Found) is treated as a health check failure

Because your React application is returning 404 for the configured health check URL, App Service correctly evaluates the application as unhealthy.

React applications typically serve only static files (for example, /index.html). If the health check path is set to a route that does not physically exist on the server (such as /health or /api/health without a backend), App Service will receive a 404 response, which causes the health check to fail.

Resolution steps:

• Configure the Health Check path to a valid URL that returns HTTP 200–299, such as /, provided that it loads successfully
• Ensure the configured health check path exists in the application and always returns a successful response
• Disable Health Check if it is not required for your scenario (Health Check is optional and mainly benefits multi‑instance apps)

Reference:
https://learn.microsoft.com/en-us/azure/app-service/monitor-instances-health-check?tabs=node

Kindly let us know if the above helps or you need further assistance on this issue.

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