Update TimeTrigger expression dynamically Azure Functions

Question

The user inputs the CRON expression from an interface. The function app should update the appsettings to reflect the user input.

My current approach

The TimerTrigger function with schedule appsetting

    [FunctionName("Cleanup")]
    public static async Task Run([TimerTrigger("%schedule%")]TimerInfo myTimer, ILogger log)
    {
        // Get the connection string from app settings and use it to create a connection.
        var str = Environment.GetEnvironmentVariable("db_connection");
        log.LogInformation($"db_connection : {str}");
    }

Setting the schedule appsetting via environment variable

    [FunctionName("SetConfig")]
    public static async Task<HttpResponseMessage> SetConfig([HttpTrigger(AuthorizationLevel.Function, "post", Route = null)]HttpRequestMessage req)
    {
        HistoryLogDeleteConfigDto data = await req.Content.ReadAsAsync<HistoryLogDeleteConfigDto>();
        Environment.SetEnvironmentVariable("schedule", data.Schedule);

        return req.CreateResponse(HttpStatusCode.OK);
    }

local.settings.json file

"Values": {
"db_connection": "Server=DESKTOP-DFJ3PBT;Database=CovalentLogger;Trusted_Connection=True;MultipleActiveResultSets=true",
"AzureWebJobsStorage": "UseDevelopmentStorage=true",
"FUNCTIONS_WORKER_RUNTIME": "dotnet",
"schedule": "*/20 * * * * *"
}

POSTMAN request body to update the schedule appsetting

{
"Schedule": "*/30 * * * * *"
}

But no luck. After sending the request from postman to update the setting, if I access the azure portal function app setting I still can see the old value.

But if I query the environmnet variable like below Environment.GetEnvironmentVariable("schedule", EnvironmentVariableTarget.Process) I can see the new expression. But in Azure portal function appsetting it stills the old value. So the job still executes based on the old schedule.

Where have I gone wrong? Thank you

silent silent · Accepted Answer · 2019-06-12T12:33:46

I don't think updating the Environment variable like that will work as the the schedule is only being read at the initialization of the Function - or when the app setting is updated on the app service. However, it should still be fairly doable. This does basically exactly what you are looking for: https://stackoverflow.com/a/50116234/1537195

Just package this in your HTTP-triggered Function (and I'd probably use Managed Identity) and you are good to go.

Update TimeTrigger expression dynamically Azure Functions

1 Answers