How to Enable/Disable Azure Function programmatically

Further to @James Z.'s answer, I've created the following class in C# that allows you to programmatically disable / enable an Azure function.

The functionsSiteRoot constructor argument is the Kudu root of your Functions application, eg https://your-functions-web-app.scm.azurewebsites.net/api/vfs/site/wwwroot/

The username and password can be obtained from "Get publish profile" in the App Service settings for your Functions.

public class FunctionsHelper : IFunctionsHelper
{
    private readonly string _username;
    private readonly string _password;
    private readonly string _functionsSiteRoot;
    private WebClient _webClient;

    public FunctionsHelper(string username, string password, string functionsSiteRoot)
    {
        _username = username;
        _password = password;
        _functionsSiteRoot = functionsSiteRoot;

        _webClient = new WebClient
        {
            Headers = { ["ContentType"] = "application/json" },
            Credentials = new NetworkCredential(username, password),
            BaseAddress = functionsSiteRoot
        };
    }

    public void StopFunction(string functionName)
    {
        SetFunctionState(functionName, isDisabled: true);
    }

    public void StartFunction(string functionName)
    {
        SetFunctionState(functionName, isDisabled: false);
    }

    private void SetFunctionState(string functionName, bool isDisabled)
    {
        var functionJson =
            JsonConvert.DeserializeObject<FunctionSettings>(_webClient.DownloadString(GetFunctionJsonUrl(functionName)));
        functionJson.disabled = isDisabled;
        _webClient.Headers["If-Match"] = "*";
        _webClient.UploadString(GetFunctionJsonUrl(functionName), "PUT", JsonConvert.SerializeObject(functionJson));
    }

    private static string GetFunctionJsonUrl(string functionName)
    {
        return $"{functionName}/function.json";
    }
}

internal class FunctionSettings
{
    public bool disabled { get; set; }
    public List<Binding> bindings { get; set; }
}

internal class Binding
{
    public string name { get; set; }
    public string type { get; set; }
    public string direction { get; set; }
    public string queueName { get; set; }
    public string connection { get; set; }
    public string accessRights { get; set; }
}

No, this is not possible currently. The disabled metadata property in function.json is what determines whether a function is enabled. The portal just updates that value when you enable/disable in the portal.

Not sure if it will meet your needs, but I'll point out that there is also a host.json functions array that can be used to control the set of functions that will be loaded (documented here). So for example, if you only wanted 2 of your 10 functions enabled, you could set this property to an array containing only those 2 function names (e.g. "functions": [ "QueueProcessor", "GitHubWebHook" ]), and only those will be loaded/enabled. However, this is slightly different than enable/disable in that you won't be able to invoke the excluded functions via the portal, whereas you can portal invoke disabled functions.

Further to @DavidGouge 's answer above, the code he posted does work, I just tested it and will be using it in my app. However it needs a couple of tweaks:

1. Remove the inheritance from IFunctionsHelper. I'm not sure what that interface is but it wasn't required.

2. Change the class definition for Binding as follows:

       internal class Binding
       {
           public string name { get; set; }
           public string type { get; set; }
           public string direction { get; set; }
           public string queueName { get; set; }
           public string connection { get; set; }
           public string accessRights { get; set; }
           public string schedule { get; set; }
       }
   

   After that it would work.

P.S. I would have put this as a comment on the original answer, but I don't have enough reputation on Stack Overflow to post comments!