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New deployed azure function returns 404 Not Found error

Troubleshooting Azure Function 404 Not Found Errors

When deploying an Azure function, you may encounter a 404 Not Found error. This error can have several causes, and the solution depends on the specific cause in your case. Here are some common causes and their respective solutions:

1. Incorrect FUNCTIONS_EXTENSION_VERSION:
  • Cause: The FUNCTIONS_EXTENSION_VERSION application setting is not set correctly.
  • Solution: Ensure that the FUNCTIONS_EXTENSION_VERSION setting is set to 3 or higher. This setting specifies the version of the Azure Functions runtime to use. If it's set to an incorrect or outdated version, you may encounter the 404 error.
2. Inconsistent IaC Configuration:
  • Cause: Your Infrastructure as Code (IaC) configuration might not be properly setting up the function app.
  • Solution: Verify that your IaC code is correctly configuring the function app. Make sure it sets the function app version to ~3, as shown in the example below:

"functionApp": {
  "name": "[functionAppName]",
  "version": "~3",
  ...
}
3. Function App Platform Mismatch:
  • Cause: The build target and Azure Function Platform configuration are mismatched.
  • Solution: Ensure that the build target matches the Azure Function Platform configuration. For example, if your function app is configured for 32-bit, your build target should also be set to win-x86 or win-x64.
4. Incompatible Package Versions:
  • Cause: You may have added a custom package with an incompatible version.
  • Solution: Verify the versions of the packages you're using. Make sure they are compatible with your project's target framework and the Azure Functions runtime version.
5. Multiple "direction": "in" Settings:
  • Cause: Having multiple "direction": "in" settings in your function.json can cause 404 errors.
  • Solution: Review your function.json and ensure that there are no duplicate "direction": "in" settings. Delete any extra settings.
6. Incorrect Scheduling Format:
  • Cause: Incorrectly formatted schedule expressions for timer triggers.
  • Solution: Use a 6-place schedule expression for timer triggers. The correct format is "0 */5 * * *", where the first 0 represents the minute, the second 0 represents the hour, and the * indicates "every" value for the rest of the fields.
7. Outdated Azure Functions Runtime:
  • Cause: Using an outdated version of the Azure Functions runtime.
  • Solution: Ensure that you're using the latest version of the Azure Functions runtime. Refer to the Microsoft documentation for the recommended runtime version.
8. Incorrect Function Binding:
  • Cause: Incorrectly configured function binding in the function.json or incorrect code logic.
  • Solution: Verify the binding configuration in your function.json and ensure that the binding information is correct. Additionally, check the code logic to ensure that it's properly handling the data received from the binding.
9. Incorrect Azure Function URL:
  • Cause: Using an incorrect URL to access the Azure function.
  • Solution: Make sure you're using the correct URL to access your Azure function. The URL should be in the format: https://<function-app-name>.azurewebsites.net/api/<function-name>.
10. Firewall or Network Issues:
  • Cause: Firewall or network configuration issues.
  • Solution: Ensure that the firewall or network configuration allows access to the Azure function. Check if there are any restrictions or blocked ports that may be preventing access to the function.
By following these steps, you can troubleshoot and resolve the 404 Not Found error when deploying Azure functions. It's essential to carefully review the error message and investigate the specific cause in your case to find the appropriate solution.

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