Overriding host.json Values in Azure Functions For Specific Environments

Have you ever ran into a situation where you’d like to modify host.json settings for only one environment? Maybe you’d like more detailed logs in your local environment or perhaps you’d like to add a custom handler?

It turns out this is a possibility and I had to do some digging to find the solution. To override host.json values for a specific environment, you can add values formatted as AzureFunctionsJobHost__path__to__setting to application settings where the double underscore (__) refers to the JSON hierarchy.

For instance, if I wanted to change the default log level to “Debug”, I can reference the sample host.json file and determine that I need to set logging.logLevel.default to “Debug”. Remember that the key always starts with AzureFunctionsJobHost and we need to use underscores to represent the JSON hierarchy.

{
    "IsEncrypted": false,
    "Values": {
        "AzureWebJobsStorage": "",
        "FUNCTIONS_WORKER_RUNTIME": "node",
        "AzureFunctionsJobHost__logging__logLevel__default": "Debug"
    }
}

Now if I run my function, you’ll notice a much more detailed output:

And there you have it! If you’d like more information on this, you can refer to the Microsoft docs on overriding host.json values.